FR2928324A1 - Braking system i.e. electronic stability program braking system, for motor vehicle, has braking managing circuit comprising accumulator permitting generation of brake pressure independent of actions of driver on control device - Google Patents

Abstract

The system has a braking managing circuit (2) e.g. stability and trajectory control device, electronically controlled by an electronic control unit. The circuit (2) has a high pressure brake fluid accumulator (10) connected to a gear motor (21) e.g. brake or irreversible type or gear motor, by mechanical connections constituted by a cable (22) and a coupling unit (23). The accumulator permits generation of brake pressure independent of actions of a driver on a control device e.g. braking pedal (100), installed at the interior of a passenger compartment. An independent claim is also included for a method for implementing a braking system.

Description

BRAKING SYSTEM WITH STABILITY AND TRACK CONTROL

FIELD OF THE INVENTION The invention relates to a hydraulically-controlled braking system for a motor vehicle, which makes it possible, in particular, to carry out the vehicle stability and trajectory control functions with relatively inexpensive means. The invention also relates to a method implemented by this system.

The invention has applications in the field of the automobile and, in particular, in the field of braking of motor vehicles.

STATE OF THE ART A vehicle generally comprises two braking control devices whose operation is independent of one another. Thus, for example, most vehicles include a mechanical control device for the secondary brake, or hand brake, and a hydraulic control device for the main brake. A conventional hydraulic control braking system comprises the following elements: an amplification element increasing the force exerted on the brake pedal by the driver, this force being called pedal force, a tandem master cylinder, which consists of a piston pump used to transform the pedal force into hydraulic pressure; for this purpose, the tandem master cylinder is in communication with a reservoir of brake fluid, - receivers located at the wheels and intended to convert the hydraulic pressure into a braking torque of the wheel, for example by a pressure force between the brake pads and the disc, in the case of disc brakes. These braking systems, although effective in stopping the wheels themselves, do not solve the problems of loss of control, stability and trajectory that may occur when a vehicle is traveling in certain areas. special conditions, for example on a damaged, slippery or icy pavement, or at a speed that is too high, or when the driver has to brake or change direction abruptly. In order to solve these problems, the car manufacturers have designed different braking force control systems.

A first type of braking force control system is an anti-lock system, which aims to prevent wheel lock when a driver brakes suddenly, in order to maintain a good grip of the wheels on the roadway in all circumstances. The principle of such systems, in particular so-called ABS (AntiBlockieren System) systems, is to use solenoid valves and hydraulic pumps to reduce the brake pressure applied to a wheel, since a risk of blockage of this wheel is detected. . Such a system comprises, for example, a speed sensor installed on each wheel, and two solenoid valves per wheel, to enable this pressure control.

Electronic stability and trajectory control systems are also known, in particular so-called ESP systems (Electronic Stability Program), the objective of which is to increase or generate a braking torque applied to a wheel as soon as a unit of electronic control, in conjunction with the engine control, in charge of the system control detects that a driver setpoint, transmitted via an action on the brake pedal, is non-existent or insufficient in view of a situation of stability of the vehicle, this situation being determined from measurements made by different sensors installed in the vehicle. In order to be able to carry out this increase or generation of braking torque without action of the driver on the pedal, it is necessary to have a power supply device, installed in the braking system, and independent of any effort of the driver. on the brake pedal. The implementation of such a power supply device is controlled, if necessary, by the electronic control unit.

Braking systems are known in which the energy supply device consists of a hydraulic pump controlled by an electronic control unit installed in the vehicle. Generally, a braking system provided with a stability and trajectory control also allows the implementation of an anti-lock system, because the elements used to increase the brake pressure on each wheel can be used, at the same time. inverse, to reduce this pressure, and thus allow the unlocking of a wheel. The operation of such a system will now be described in relation to FIG. 1. This figure represents a braking configuration according to a single circuit of the vehicle, ie only for two wheels, the second circuit being identical for both other wheels. As a simplification of the figure, the electronic control unit, which controls the various modulations of braking forces according to data provided by different sensors of the vehicle, has not been shown. The braking system shown in Figure 1 comprises all the elements of a conventional hydraulic braking system, as described above. Such a braking system comprises a first brake management circuit 1, controlled by the driver of the vehicle from the brake pedal 100, and a second brake management circuit 2, controlled by the electronic control unit. More precisely, the first braking management circuit 1 comprises the following elements: a brake pedal 100, intended to transmit and amplify the force exerted by the driver of the vehicle when he wishes to brake, a booster 101, to amplify the braking force of the driver, - a tandem master cylinder 102, connected to a brake fluid reservoir 115 and making it possible to transform the force amplified by the booster and the pedal into hydraulic pressure, and - a sensor of pressure 113. It also comprises, for each wheel or set of two wheels, a brake fluid intake and exhaust system. The intake and exhaust circuits and the brake management circuits each comprise one or more solenoid valves and a set of hydraulic pipes, not referenced, for channeling the fluid, namely the brake fluid, between the different elements of the system. In the description, solenoid valve is called an electrically controlled valve.

It is specified here that, unless otherwise indicated, the solenoid valves used may be of all-or-nothing or proportional type. An all-or-nothing solenoid valve has two positions, a rest position, called normal position, in which it is located when it is not activated, and an activation position. In the normal position, a solenoid valve can be opened, circulating the fluid, or closed, preventing the flow of fluid. Thus, a normally open solenoid valve allows the fluid to pass when it is not activated and, on the contrary, blocks the passage of the fluid when it is electrically activated. A proportional solenoid valve can take an infinite number of positions between the open position and the closed position, which allows a progressive opening or closing of the solenoid valve to control the flow of brake fluid. It may also be solenoid valve flow, that is to say, to control a flow, or pressure solenoid valve, that is to say, to control the pressure difference applied to this solenoid valve. The first braking circuit 1 comprises in particular a control electrovalve 105, normally open. The second brake management circuit comprises in particular a suction electrovalve 106, normally closed. It further comprises a hydraulic pump 107. The first and second brake management circuits also each comprise a valve, respectively 108, 109, allowing to allow the passage of fluid in one direction.

The intake and exhaust circuit 3 comprises: a low-pressure accumulator 110, intended to temporarily store fluid during certain operating phases of the system; at each brake caliper, a circuit comprising two solenoid valves; one being a normally open intake solenoid valve (111a, 111b), and the other a normally closed exhaust solenoid valve (112a, 112b), as well as a check valve (114a, 114b), and - receivers 103a and 103b (stirrups), associated with the brake discs 104a and 104b, for converting the hydraulic pressure into a braking torque of each of the wheels. During a conventional braking, in which the stability and trajectory control is not used, all the solenoid valves are deactivated, that is to say that they are in their normal position. The operation is then as follows: when the driver presses the pedal 100, as previously described, a pressurized fluid is emitted at the output of the tandem master cylinder 102, this fluid passes through, on the one hand, the solenoid valve 105 and, on the other hand, the valve 108, the fluid is then directed, via the network of hydraulic lines, towards the receivers 103a and 103b, via the solenoid valves 111a and 111b, the fluid under pressure is thus introduced into the stirrups 103a and 103b, which ensures the braking of each of the wheels. During a conventional brake release, that is to say when the driver reduces the force on the brake pedal 100, the pressurized fluid contained in the stirrups 103a and 103b is redirected to the tandem master cylinder 102, via the solenoid valves 111a and 111b and the valves 114a and 114b. When a risk of blockage of a wheel is detected, for example of the wheel bearing the caliper 103a, it is advisable to reduce the pressure in this caliper, in order to proceed with the release of this wheel. Such a blocking generally follows a too great braking action with respect to the conditions of adhesion. To effect this reduction in pressure, the electronic control unit controls the normally closed, normally open, and normally closed exhaust valves 111a to become closed and open respectively.

As a result, the pressurized fluid contained in the lug 103a flows via the solenoid valve 112a to the low pressure accumulator 110. This low pressure accumulator 110 temporarily stores the fluid evacuated by the exhaust solenoid valves 112a and 112b of the calipers 103a and 103b. The valve 109 installed between the accumulator 110 and the suction pump 107, and allowing the flow of the brake fluid in the accumulator => pump direction allows the pump 107 to empty and thus reduce the pressure of the pump. accumulator 110 when needed. In the opposite case, where the driver does not exert any force on the brake pedal or that he exerts an insufficient force on the brake pedal with respect to the situation of the vehicle, the electronic control unit detects that the pressure in The output of the master cylinder, measured by the sensor 113, is less than the pressure required to maintain good vehicle stability. It then controls the activation of the control solenoid valve 105, which closes, which has the effect of isolating the master cylinder 102 of the braking circuit. The suction solenoid valve 106, placed between the master cylinder 102 and the suction of the hydraulic pump 107, is also activated and is then in the open state. The pump 107 is thus connected to the master cylinder 102 and can take (aspirate) fluid directly at the master cylinder 102 or its reservoir 115. The electronic control unit then controls an operation of the hydraulic pump 107 , in order to send fluid under pressure towards the inlet solenoid valve 111a or 111b corresponding to the wheel on which it is necessary to apply a larger braking pressure. A system of this type is relatively effective in remedying the loss of stability and trajectory that can occur with a vehicle. However, with such a system, the maximum pressure is obtained, in the brake elements, with a delay time compared to the command issued by the electronic control unit. In addition, the system described above is composed of relatively expensive elements, which, at present, make it difficult to install serially on all vehicles produced by car manufacturers.

DISCLOSURE OF THE INVENTION The object of the invention is precisely to remedy the disadvantages of the techniques described above. To this end, the invention proposes a braking system with stability control and trajectory, also called ESP (Electronic Stability Program), made without pump, which reduces the cost of the basic elements of said system, while allowing a relatively simple installation. For this purpose, the invention proposes a braking system in which the second braking management circuit comprises, in place of the hydraulic pump, an organ in which potential energy is stored and restored during the phases requiring a pressure of braking independent of the action of the driver. In the invention, this member is in the form of a high pressure accumulator associated with a geared motor traction system. Such a member provides a maximum pressure in the system, almost immediately, which allows to consider additional functions for the braking system. More specifically, the invention relates to a hydraulically-controlled braking system for a motor vehicle comprising: a first intake and exhaust circuit for the brake fluid in at least one brake element, a first management circuit braking system, controlled by a driver of the vehicle from a control device installed inside the passenger compartment, and - a second braking management circuit, electronically controlled by an electronic control unit, - the first and the second braking management circuit being connected to the intake and exhaust circuit of the brake fluid, characterized in that the second braking management circuit comprises a connected brake fluid accumulator, via a mechanical connection, to a geared motor, the accumulator being capable of supplying brake fluid under pressure and making it possible to generate a braking pressure independently of the actions of u driver on the control device installed inside the cockpit. The invention may also include one or more of the following features: the second brake management circuit comprises a solenoid valve, normally closed, placed at the outlet of the high pressure accumulator, the first brake management circuit comprising a master cylinder and a solenoid valve, normally open, placed at the output of said master cylinder. the system comprises a solenoid valve with 3 orifices, of all or nothing type, placed at the same time at the output of the high pressure accumulator and at the output of the master cylinder. the high-pressure accumulator comprises at least one piston associated with a spring and connected to the gearmotor via the mechanical link so that the gearmotor, by moving the piston, ensures the compression of the spring as well as the circulation of the liquid of brake inside an enclosure of the accumulator. the high-pressure accumulator comprises a force sensor able to determine a level of pressure potentially available in the accumulator. - The system includes a torque limiter built into the gearmotor or mechanical connection to control the compression force of the spring and therefore the pressure potentially available in the accumulator. the mechanical connection comprises, for example, a cable connecting the piston of the accumulator to the geared motor. the geared motor is of the braked or irreversible type. In the case of an irreversible geared motor, the system comprises a coupling means for separating the geared motor traction system. - The geared motor is reversible type and the piston is equipped with a mechanical locking means. the system comprises a pressure sensor placed upstream of the intake and exhaust circuit for determining the hydraulic pressure transmitted to the brake elements. the second brake management circuit comprises a hydraulic amplifier. the intake and exhaust circuit comprises, at its outlet, a low pressure accumulator able to temporarily store brake fluid discharged from the brake elements and to transfer this accumulated brake fluid, when the conditions allow it, at the first braking management circuit. - The first braking management circuit comprising a master cylinder associated with a brake fluid reservoir, the outlet of the intake and exhaust circuit is connected directly to the brake fluid reservoir. the normally open piloting solenoid valve (105) is interposed between the master cylinder (102) and valves (114a, 114b) of the intake circuit so as to form a braking circuit distinct from the braking circuit. the system comprising a second brake fluid intake and exhaust circuit, also connected to a second brake management circuit, the second brake management circuit connected to the second intake and exhaust circuit comprises a high pressure brake fluid accumulator connected to the geared motor - the high pressure accumulators of each of the second brake management circuits are connected to a single lifter, said lifter being connected by a mechanical connection to the geared motor. The invention also relates to a method for implementing the system described above, characterized in that it comprises the following operations: a pressure potentially available in the accumulator is compared with a predetermined threshold value, when the potentially available pressure is below the threshold value, the gearmotor is activated, - under the action of the geared motor, the piston of the high pressure accumulator moves, sucking brake fluid into the high pressure accumulator, - as soon as the pressure potentially available has reached the threshold value, the geared motor is deactivated, - the piston (11) is held in position as long as the control unit does not require any pressure independently of the action of the driver on the control device (100) installed at the interior of the passenger compartment, the potentially available pressure is thus preserved even if the hydraulic pressure of the accumulator can iminuer.

The method of the invention may also include one or more of the following features: - when the system comprises a valve in parallel with the normally closed solenoid valve 106, said solenoid valve may not be activated when the geared motor is activated - when the system does not comprises no valve in parallel with the normally closed solenoid valve 106, said solenoid valve must be activated before the gearmotor is activated. - When the system does not include a normally closed valve or solenoid valve 106, the gearmotor is activated directly. the method comprises a preliminary operation for determining the pressure potentially available in the accumulator from a measurement of a traction force of the piston, carried out by means of a force sensor, and a measurement of a pressure of the master cylinder, performed by means of a pressure sensor. the method comprises a preliminary operation for determining a potentially available pressure in the accumulator from a maximum torque transmissible by a torque limiter. The invention further relates to a motor vehicle characterized in that it comprises the system described above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, already described, represents a braking circuit with stability control and a conventional trajectory.

FIG. 2 represents an example of a hydraulically controlled braking system according to the invention. FIGS. 3A to 3D show the braking system of FIG. 2, on which is indicated the direction of circulation of the brake fluid during different phases of operation.

Figures 4 to 8 show various embodiments and variants of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION An example of a braking system according to the invention is shown in FIG. 2. As in the prior art, the braking system of the invention comprises a circuit 3 for admission and exhaust of the brake fluid. In the embodiment described below, the intake and exhaust circuit 3 is associated with two brake elements, that is to say two wheels of the vehicle.

This intake and exhaust circuit 3 is connected, on the one hand, to a first braking management circuit 1 and, on the other hand, to a second braking management circuit 2. The first braking management circuit 1, also called a pedal braking device, is controlled by the driver of the vehicle from a control device installed in the passenger compartment of the vehicle. This control device may be a brake pedal or a manual actuator, mechanical or electrical or electromechanical. The second braking management circuit 2, also called stability and trajectory control device, is controlled electronically by an electronic control unit. In the invention, the first braking management circuit 1 comprises, as previously described, a booster 101, a master cylinder 102 associated with a brake fluid reservoir 115 and a solenoid valve 105. As explained in more detail below, the first brake management circuit also comprises a pressure sensor 113. This pressure sensor 113 is placed upstream of the intake and exhaust circuit 3 to determine the hydraulic pressure transmitted to the brake elements. It can be placed, for example, at the outlet of the master cylinder 102 or at the outlet of the solenoid valve 105, as shown in FIG.

In the invention, the second brake management circuit 2 is made with relatively simple elements to install on the vehicle and relatively inexpensive compared to the price of a hydraulic pump. This second brake management circuit comprises a brake fluid accumulator 10. A high pressure accumulator is an accumulator for delivering fluid at pressures of the order of 100 to 150 bar, as opposed to the low pressure accumulator 110 whose hydraulic pressure is of the order of 0 to 15 bar. The high pressure accumulator is calibrated at a pressure of 100 to 150 bar, that is to say that the preload force of the spring or springs on the piston provides a pressure of 100 to 150 bar. The high pressure accumulator 10 of the invention comprises an enclosure 14 provided with an orifice 16 through which the brake fluid can enter the accumulator or exit said accumulator. It further comprises at least one piston 11 inserted inside the enclosure 14. The piston 11 is a movable member with rectilinear movement inside the enclosure 14.

The piston 11 has a shape that can be substantially T; it comprises a piston head 11b and a piston rod 11a. In the invention, the piston 11 is associated with a spring 12. This spring 12 can be mounted around a piston rod 11a, between the piston head 11b and an abutment 15 formed inside the piston. pregnant. When the spring is compressed between the piston head 11b and the stop 15, brake fluid can enter the accumulator 10. As long as the spring 12 is in its compressed position, the brake fluid is stored in the reservoir. accumulator. The compression of the spring 12 makes it possible to store energy in potential form in the accumulator 10. It is this potential energy which ensures the pressurization of the fluid in the said accumulator 10. When the spring 12 expands, the piston 11 is pushed towards the port 16 of the accumulator, discharging the brake fluid towards said orifice 16. The brake fluid, stored until now in the accumulator 10, is then discharged from said accumulator through the orifice 16, with a sufficient pressure to enable it to reach the brake elements 103. The compressed and relaxed positions of the spring 12 are obtained, in the invention, by means of a traction system 20. This traction system 20 comprises a geared motor 21 connected to the high pressure accumulator 10 via a mechanical connection 22/23. This mechanical connection 22/23 is fixed on the piston rod 11a. The geared motor 21 is a rotary motor for driving, via the mechanical connection 22/23, the piston 11 of the high pressure accumulator. When the gearmotor is activated, that is to say in motion, it drives the connection 22/23, and consequently the piston 11 which compresses the spring 12. As explained above, the fact of moving the piston 11 towards the stop 15 allows to release the orifice 16 and to introduce brake fluid into the chamber of the accumulator 10. As will be seen later, the geared motor is preferably irreversible; thus when the gearmotor 21 is deactivated, the spring 12 remains compressed. On the other hand, when the gearmotor is released, the spring 12 expands, driving the piston head 11b towards the orifice 16, which has the effect of driving the brake fluid towards the hydraulic lines external to the accumulator 10. with a pressure which depends, in particular, on the compressive force undergone by the spring 12.

In a preferred variant of the invention, the geared motor 21 is connected to the high pressure accumulator 10 via a cable 22 associated with a coupling means 23. This coupling means makes it possible to separate the control system. traction of the geared motor, when the gearmotor is irreversible type. The cable 22 and the coupling means 23 form the mechanical connection 22/23. The traction system may comprise a pulley or a set of pulleys arranged so as to increase the reduction ratio of the traction system while decreasing the stress on the cable.

According to a variant of the invention, the pistons constituting the high pressure accumulator of each of the two circuits are interconnected by a spreader, which is itself connected to the gearmotor 21 by the cable 22 and thus by the coupling means 23. variant makes it possible to have only one traction element for all the braking systems of the vehicle. In a preferred embodiment of the invention, the high pressure accumulator 10 also comprises a force sensor 13. This force sensor 13 can be placed between the piston 11 and the traction system 20, for example between the cable 22 of the mechanical connection and the piston rod 11a.

The force sensor 13 makes it possible to estimate the pressure that is potentially available in the accumulator 10 when the spring 12 is released. Indeed, the information provided by the force sensor 13 relates to the displacement of the piston 11 inside the enclosure 14, this displacement making it possible to estimate the pressure force with which the brake fluid will be evacuated. enclosure 14. An alternative embodiment with a displacement sensor of the piston or the traction system is also possible. In other words, the force sensor 13 makes it possible to know if, at a given moment, the pressure potentially available thanks to the high pressure accumulator 10 is sufficient to allow the realization of the functions requiring a braking pressure independently of the action of the driver on the brake pedal 100 or, conversely, if it is insufficient. This information is necessary, in particular, at the start of the vehicle or after braking controlled by the electronic control unit. In such an embodiment, this information can be used to indicate to the driver, by means of a bulletin board (light (s), message (s) ...), if the stability control device and trajectory is in an optimal operating state or not. In an alternative embodiment, this information is transmitted to a safety device which prevents the engine from starting as long as the pressure potentially available thanks to the high pressure accumulator 10 necessary for the safety of the vehicle and its occupants has not been reached. The force sensor 13 may also make it possible to diagnose a rupture of a cable and / or springs. The rupture of a cable does not involve unwanted braking since the chamber of the high pressure accumulator 10 is isolated from the braking circuit by the solenoid valve 106 and the valve 116. Thus, with such a braking system, the braking process is as follows: - when the driver of the vehicle wishes to brake, it exerts a force 200 on the brake pedal 100; this force is amplified by the brake pedal 100 as well as the booster 101 and then transmitted to the master cylinder 102. The master cylinder 102 generates a hydraulic pressure depending on the effort received. The brake fluid under pressure is transmitted through a set of hydraulic lines to the intake and exhaust circuit 3. More specifically, the brake fluid under pressure is transmitted to the circuit 3 via a valve 108 and a solenoid valve 105. In its normal state, the solenoid valve 105 is open allowing the passage of the fluid of the master cylinder 102 to the circuit 3. The hydraulic pressure is thus transmitted to the brake elements 103a and 103b. The circulation of the brake fluid from the master cylinder 102 to the brake members 103a and 103b, in the case of braking by the driver, is represented by an arrow in FIG. 3A. - When a brake release, that is to say when the driver reduces or stops exerting a force 200 on the brake pedal, the brake fluid contained under pressure in the brake elements 103a, 103b, returns to the master cylinder 102, as shown in Figure 3B. The return of the brake fluid is effected through the normally open valves 114a, 114b and solenoid valves 111a, 111b of the circuit 3. It then passes through the solenoid valve 105 to reach the master cylinder 102. vehicle, when controlled by the electronic control unit, will now be described through Figures 3C and 3D. FIG. 3C represents the braking system of the invention during the energy storage phase in the high pressure accumulator 10. In this FIG. 3C, the circulation of the brake fluid between the reservoir 115 and the high pressure accumulator 10 is represented by an arrow As explained above, the force sensor 13 of the high pressure accumulator 10 makes it possible to determine whether the level of force exerted by the spring 12 on the piston 11 is sufficient or not to allow the realization of the stability and trajectory control functions, or more generally requiring a braking pressure independent of the action of the driver on the brake pedal 100. The level of effort may be insufficient, for example, at the time of starting the vehicle or after using the system to make a correction of the vehicle trajectory. In such a case, when the level of effort is insufficient, the solenoid valve 106 and the gear motor 21 are activated. The geared motor then exerts a traction force on the piston 11 via the mechanical link 22/23. In moving, the piston 11 compresses the spring 12. In parallel, the movement of the piston has the effect of sucking brake fluid into the accumulator 10. This brake fluid comes from the reservoir 115, through the solenoid valves 105 and 106 and the valves 108 and 116. When the force sensor 13 measures that the level of force exerted by the spring 12 on the piston 11 is sufficient, the solenoid valve 106 and the gear motor 21 are deactivated. As explained above, when the gearmotor is deactivated, the traction force established by the geared motor on the piston is retained. The energy supplied by the geared motor 21 to the traction system is thus transformed and stored in potential form in the spring 12 of the high pressure accumulator 10. This potential energy will make it possible to generate the pressure required to provide a trajectory control for example. since the piston 11 will be released. Thus, the braking system of the invention implements the following method: the pressure potentially available thanks to the accumulator 10 is compared with a predetermined threshold value, when the potentially available pressure is below the threshold value, the The operation may be slightly different according to the embodiments: o If the system comprises a valve 116, the solenoid valve 106 may not be activated but the gearmotor 21 is activated. o If the system does not include a valve 116, the solenoid valve 106 must be activated then the gear motor 21 is activated. o If there is no valve 116 or electrovalve 106, the geared motor 21 is directly activated. under the action of the gearmotor 21, the piston 11 of the high pressure accumulator moves, sucking brake fluid into the high pressure accumulator, - as soon as the potentially available pressure has reached the threshold value, the geared motor 21 is deactivated and the solenoid valve 106 if it was previously active, - the piston 11 is held in position as the control system does not require pressure regardless of the action of the driver on the pedal 100. The potentially available pressure is therefore preserved even if the hydraulic pressure of the accumulator can be reduced (under the effect of the leaks of the solenoid valve 106 and / or the valve 116). This method comprises a preliminary operation for determining the pressure potentially available in the accumulator. This determination can be made from a measurement of a pulling force of the piston, carried out by means of the force sensor 13, and a measurement of a pressure of the master cylinder, carried out by means of the pressure sensor. 113. It can also be performed from a maximum torque transmissible by a torque limiter.

In a preferred embodiment of the invention, the geared motor 21 is of irreversible type, or braked. In this case, it maintains the traction force on the piston 11 and therefore the compression force of the spring 12 until it is released. In another embodiment of the invention, the geared motor 21 is of the reversible type. In this case, the tensile force of the piston 11 is maintained by a mechanical locking system of the piston 11 of the accumulator 10. This mechanical locking system may, for example, consist of a rack and pinion assembly with freewheel associated with a brake.

When the electronic control unit issues an activation command of the second brake management circuit 2, the piston 11 is released. The spring 12 can then relax by exerting a force on the piston 11 which consequently generates a hydraulic pressure. This pressure can be controlled by means of the solenoid valve 106 or the intake solenoid valves 111a and 111b. The fluid flow caused by the displacement of the piston 11 in the chamber 14 of the accumulator 10 is represented by the arrows in FIG. 3D. The pressurized brake fluid passes through the solenoid valve 106 and the hydraulic lines to the intake and exhaust circuit 3, then passes through said circuit 3 to the brake elements 103a and / or 103b. Throughout this phase of operation and to be able to generate a hydraulic pressure in the braking circuit, the normally open solenoid valve 105 is activated (closed). If during this phase of operation the driver presses on the brake pedal 100, the pressure resulting from this action can be transmitted to the brake elements, if it is greater than the pressure modulated by the solenoid valve 106 or by the solenoid valves 111. a and 111b, via the valve 116. It should be noted that, when the stability control device is actuated, it has the effect of modifying the hydraulic pressure in certain brake elements by increasing or decreasing it . The four brake elements of the vehicle can then have a different hydraulic pressure. In the example of FIG. 3D, there is shown the case where the hydraulic pressure is increased in the two brake elements 103a and 103b, it being understood that the hydraulic pressure in one or both element (s) brake could be kept constant or decreased via the intake solenoid valves 111a and 111b and exhaust 112a and 112b (as in the case of braking with anti-lock wheels). When it is necessary to reduce the pressure in a brake element, the normally open intake solenoid valve 111 and the normally closed exhaust solenoid valve 112 associated with the brake element concerned are activated. , simultaneously or not. In one embodiment of the invention, the brake fluid then flows via the valve 117 to a low pressure accumulator 110. This accumulator 110 is called a low pressure accumulator, as opposed to the high pressure accumulator. 10 because its internal pressure is much lower than that of the high pressure accumulator. This low pressure accumulator 110 is connected by a valve 109 to the inlet of the intake and exhaust circuit 3. It can also be connected, by said valve 109, to the output of the master cylinder 102, as shown in Figure 7A. Since the valve 109 only allows the flow to flow in one direction only, ie from the low pressure accumulator 110 to the braking management circuits 1 and 2, the pressure of the low pressure accumulator 110 may be lower than the pressure of the master cylinder 102. The low pressure accumulator 110 is sized in volume and stiffness so that it can store the entire volume of brake fluid discharged from the brake elements by the solenoid valves 112 exhaust, during regulation, while having a relatively low pressure rise. The low pressure accumulator 110 is then emptied, via the valve 109, when, during release, the pressure of the master cylinder 102 becomes lower than the pressure of the low pressure accumulator 110. In another embodiment of the invention, when it is necessary to lower the pressure in a brake element, the excess brake fluid flows through the exhaust solenoid valves 112 and directly to the reservoir 115 of the master cylinder 102. effect, in this embodiment, shown in Figure 8, the output of the intake and exhaust circuit 3, that is to say the valves 117a and 117b, is connected directly by a hydraulic line, to the reservoir 115 of brake fluid. There is no low pressure accumulator to store the brake fluid while waiting for the next brake release. Thus, in this embodiment, the brake fluid returns directly to the reservoir 115 of the master cylinder instead of being stored in a low pressure accumulator and then discharged to the reservoir 115. This embodiment avoids the constraints relating to the volume of the low pressure accumulator. It also simplifies the operation and control of the braking system. The return line between the valves 117 and the reservoir 115 may be specific to each of the intake and exhaust circuits (each corresponding to two wheels of the vehicle) or share by the two circuits. There is only one return line for all 4 wheels. It should be noted that the various variants of the invention described above, relating for example to the traction system, can be implemented regardless of the embodiment of the intake and exhaust circuit 3 (ie with or without a low pressure accumulator). Other variants of the invention, which will be described below, may also be considered, regardless of the embodiment of the circuit 3 intake and exhaust. Alternatively, the traction system 23 of the invention may be a winch, as shown in Figures 2 and 3. This traction system 23 may also be formed of a pinion and rack assembly, as shown in Figure 4 In this case, the traction system can be directly connected to the piston of the high-pressure accumulator 10. The traction system 23 can also be realized by means of a worm, as shown in FIG. variant of the invention, the force sensor 13 described above can be replaced by an integrated torque limiter, either the gear motor 21 or the traction system 23. In this variant, the traction force is not controlled electronically, thanks to the information provided by the force sensor, but by limiting the torque. In another variant, the force sensor 13 is replaced by a linear displacement sensor or an angular displacement sensor.

According to a variant of the invention, a hydraulic amplifier 18 is inserted on the hydraulic line connecting the high pressure accumulator 10 to the intake and exhaust circuit 3. This hydraulic amplifier 18 has the role of increasing the pressure at the outlet of the high pressure accumulator 10. This hydraulic amplifier 18 can be installed either between the solenoid valve 106 and the high pressure accumulator 10, as represented in FIG. 6A. or between the solenoid valve 106 and the hydraulic line joining the intake and exhaust circuit 3, as shown in Figure 6B. In the above description, the solenoid valves of the braking management circuits 1 and 2, namely the solenoid valves 105 and 106, are two-port solenoid valves. These solenoid valves 105 and 106 may be replaced by a single three-hole solenoid valve 118, as shown in FIG. 7B. This solenoid valve 118 is all-or-nothing type. Control of the pressure in the stirrups is then performed by the intake solenoid valves 111a and 111b. The solenoid valve 118 makes it possible to connect the intake and exhaust circuit 3 with either the accumulator 10 or with the master cylinder 102. In this case, it is possible to move the valve 116, as shown in FIG. 7C, see to delete it. It is also possible to directly connect the valve 109 to the master cylinder 102, as shown in Figure 7D. It is also possible to directly connect the valve 109 to the master cylinder 102 and remove the valve 116, as shown in Figure 7E. In other alternative embodiments, the valves 114a and 114b can be connected to the solenoid valve 105 without connection with the valve 108.

Thus, the normally open piloting solenoid valve 105 is interposed between the master cylinder 102 and the valves 114a, 114b of the intake circuit. These configurations make it possible to obtain a specific braking circuit distinct from the braking circuit. Figure 7F illustrates an embodiment of this type having in addition the valve 109 directly connected to the master cylinder 102. In the embodiment of Figure 7F, the valve 116 and the solenoid valve 106 can also be removed. The valve 109 may also be connected to the solenoid valve 105 instead of the master cylinder 102. The valve 116 and the solenoid valve 106 may also be omitted. Figure 7G corresponds to this embodiment but retaining a solenoid valve 106. In another variant of the invention, one or more restrictions can be added to different locations of the hydraulic circuit. The restriction is a section change of the hydraulic line. A restriction may be added, for example, between the high pressure accumulator 10 and the point A located at the outlet of the solenoid valve 106, as shown in FIG. 7A. According to this variant, the valve 116 may be in series or in parallel with this restriction. In the above description, only one hydraulic circuit is described which manages the pressure in two brake elements (brake elements 103a and 103b). Another hydraulic circuit, identical, can be mounted on the vehicle to manage the hydraulic pressure in the other two brake elements of said vehicle. In other words, the braking system of the invention then comprises two intake and exhaust circuits and two second braking management circuits. However, it comprises a single first braking management circuit. In one embodiment of the invention, it is possible to use, for the two hydraulic circuits, one and the same traction system. In other words, each hydraulic circuit has its own high pressure accumulator but the pistons of these two high pressure accumulators are connected by the same mechanical connection to the same geared motor. For this, the pistons of the two accumulators can be connected to a rudder, itself connected to the mechanical connection.

Claims (7)

A hydraulically-controlled braking system for a motor vehicle comprising: a first circuit (3) for the intake and exhaust of a brake fluid into at least one brake element (103); a first circuit (1); ) brake management, controlled by a driver of the vehicle from a control device (100) installed inside the passenger compartment, and - a second circuit (2) brake management, electronically controlled by a electronic control unit, - the first and second braking management circuits being connected to the intake and exhaust circuit of the brake fluid, characterized in that the second braking management circuit (2) comprises an accumulator ( 10) brake fluid connected, via a mechanical link (22/23), to a geared motor (21), the accumulator for generating a brake pressure independently of the actions of the driver on the control device (100) installed inside the cockpit. 2 - System according to claim 1, characterized in that the second brake management circuit comprises a solenoid valve (106), normally closed, placed at the output of the high pressure accumulator, the first brake management circuit comprising a master cylinder (102) and a solenoid valve (105), normally open, placed at the output of said master cylinder. 3 - System according to claim 1, characterized in that it comprises a solenoid valve (118) with 3 orifices, all or nothing type, placed at the output of the high pressure accumulator (10) and at the output of the master cylinder (102). 4 û System according to any one of claims 1 to 3, characterized in that the high pressure accumulator (10) comprises at leasta piston (11) associated with a spring (12) and connected to the geared motor via the mechanical connection so that the geared motor, by moving the piston, ensures the compression of the spring (12) and the circulation of the brake fluid inside a chamber (14) of the accumulator. 5 ù System according to any one of claims 1 to 4, characterized in that the high pressure accumulator (10) comprises a force sensor (13) capable of determining a pressure level in the accumulator. 6 - System according to any one of claims 1 to 4, characterized in that it comprises a torque limiter integrated gear motor or the mechanical connection. 7 ù System according to any one of claims 4 to 6, characterized in that the mechanical connection (22/23) comprises a cable (22) connecting the piston (11) of the accumulator to the geared motor (21). 20. System according to any one of claims 1 to 7, characterized in that the geared motor is of the braked or irreversible type. 9. The system of claim 8, characterized in that it comprises a coupling means allowing, when the gearmotor is of irreversible type, to separate the mechanical connection of the geared motor. 10 - System according to any one of claims 1 to 9, characterized in that the geared motor is reversible type and the piston is equipped with a mechanical locking means. 11 - System according to any one of claims 1 to 10, characterized in that it comprises a pressure sensor (113) placed upstream of the intake and exhaust circuit to determine the hydraulic pressure transmitted to the brake elements . 3512 - System according to any one of claims 1 to 11, characterized in that the second brake management circuit comprises a hydraulic amplifier (18). 13 - System according to any one of claims 1 to 12, characterized in that the intake and exhaust circuit comprises, at its output, a low pressure accumulator (110) adapted to store temporarily the brake fluid escaping from the brake elements and returning it to the first braking management circuit. 14 - System according to any one of claims 1 to 12, wherein the first braking management circuit comprises a master cylinder (102) associated with a brake fluid reservoir (115), characterized in that the output of the circuit intake and exhaust is connected directly to the brake fluid reservoir. 15 - System according to any one of claims 2 to 14, characterized in that the normally open control solenoid valve (105) is interposed between the master cylinder (102) and valves (114a, 114b) of the circuit of intake to form a brake release circuit separate from the braking circuit. 16 û Hydraulically controlled braking system for a motor vehicle according to any one of the preceding claims, further comprising a second brake fluid intake and exhaust circuit, also connected to a second braking management circuit, characterized in that the second braking management circuit connected to the second intake and exhaust circuit comprises a high-pressure brake fluid accumulator connected to the geared motor 17. The system according to claim 16, characterized in that the high-pressure accumulators of each of the second braking management circuits are connected to a single rudder, said rudder being connected by a mechanical connection to the gearmotor.3518 - A method of implementing the system according to any one of claims 4 to 17, characterized in that 'it comprises the following operations: - a potentially available pressure in the accumulator (10) is compa to a predetermined threshold value, -when the potentially available pressure is below the threshold value, the geared motor is activated, - under the action of the geared motor (21), the piston (II) of the high pressure accumulator moves, suction of the brake fluid in the high-pressure accumulator, - as soon as the potentially available pressure has reached the threshold value, the geared motor (21) is deactivated, - the piston (11) is kept in position as long as the control unit does not require pressure independently of the action of the driver on the control device (100) installed inside the passenger compartment, the potentially available pressure is thus preserved even if the hydraulic pressure of the accumulator can decrease. 19 - The method of claim 18, characterized in that, when the system comprises a valve (116) in parallel with the solenoid valve (106) normally closed, said solenoid valve (106) may not be activated when the geared motor (21) is activated 20 ù A method according to claim 18, characterized in that, when the system does not include a valve (116) in parallel with the electrovalve (106) normally closed, said solenoid valve (106) must be activated before the geared motor (21) is enabled. 21. The method of claim 18, characterized in that, when the system comprises neither valve (116) nor solenoid valve (106) normally closed, the geared motor (21) is activated directly. 22 - Process according to any one of claims 18 to 21, characterized in that it comprises a preliminary operation for determining the pressure potentially available in the accumulator from a measurement of a traction force of the piston, carried out by means of a force sensor (13), and a measurement of a pressure of the master cylinder, performed by means of a pressure sensor (113). 23 - Process according to any one of claims 18 to 21, characterized in that it comprises a preliminary operation for determining a potentially available pressure in the accumulator from a maximum torque transmissible by a torque limiter. 24 ù Motor vehicle characterized in that it comprises a system according to any one of claims 1 to 17.