Abstract:
The present invention relates mainly to a brake booster that is adjustable, notably in terms of the value of the jump. 
     Advantageously, according to the invention, the “target” value for equilibrium of operation of the booster actuator is altered. A target value of a signal delivered by a position sensor is defined either by programming the electronic control unit or by selecting a coefficient in a program as a function of the braking characteristic or characteristics that it is desired to implement. Once the setpoint value has been determined, the electronic control unit commands the actuator using a setpoint value so that the actuator permanently and dynamically works toward achieving the previously defined and/or selected target value. The setpoint may be calculated as a function of torque, force, position or some other parameter. 
     The invention applies notably to the automotive industry. 
     The invention applies mainly to the braking industry.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates mainly to a brake booster that is adjustable, notably in terms of the value of the jump. 
         [0002]    It is known practice to produce brake boosters that apply a force to a push rod of a master cylinder which force is an increasing function of the force applied by the driver to a control rod via a brake pedal. Typically, for a range of use, the boost ratio which is the ratio between the input force applied to the control rod and the output force from the booster and applied to the push rod, is constant. It is commonplace for several ranges of use to be employed, with several boost ratios, a first boost ratio for comfortable braking and a second boost ratio, higher than said first boost ratio, for emergency braking. 
         [0003]    Among brake boosters of the known type, mention may, nonlimitingly, be made of vacuum pneumatic brake boosters, pressurized pneumatic brake boosters, hydraulic brake boosters (also known as hydroboost brake servos) as described, for example, in FR 2 727 370 and 49 49 61 846, pneumatic brake boosters with decoupling between the control rod and the push rod, like the one described, for example, in patent applications WO 2007/080106 and WO 2007/080158, and electric brake boosters like the one described in French patent application published under the number FR-2 860 474. Also known are brake boosters which further comprise means of commanding braking that are independent of the force applied by the driver to the brake pedal and widely known even in other languages by their English name of “active boosters”. One example of such a pneumatic booster is described in patent EP 0 478 396. 
         [0004]    Brake boosters are also described in documents DE 10 2006 030168, WO 03/066405 and EP 0 716 969. 
         [0005]    In the known way, the boost ratio is regulated by a reaction device, notably a reaction disk made of non-compressible elastomer or a small-diameter piston on which the pressure of a rear chamber of the master cylinder is applied. 
       SUMMARY OF THE INVENTION 
       [0006]    The Applicant Company has discovered that brake boosters of known type have their stroke controlled in terms of the relative position between a plunger driven by the control rod and a drive means, typically a piston, of the push rod that applies a force to a primary piston of a master cylinder. 
         [0007]    The Applicant Company has discovered that, in the prior-art system, the booster always ensures dynamic equilibrium between the action and the reaction, notably in terms of the relative position of the control means, typically a three-way valve in the context of a pneumatic booster. 
         [0008]    The Applicant Company has concluded from this that the dynamic equilibrium of known type limits the ways in which boosters of known type can operate. 
         [0009]    The booster according to the present invention has means making it possible to create a non-zero offset and/or a variation, on command, for example at the command of an electronic control unit, between the position of equilibrium of the forces of reaction between the control means, typically a plunger and/or a control rod, and the means of applying force of the booster. 
         [0010]    Advantageously, according to the invention, the “target” value for equilibrium of operation of the booster actuator is altered. A target value of a signal delivered by a position sensor is defined either by programming the electronic control unit or by selecting a coefficient in a program as a function of the braking characteristic or characteristics that it is desired to implement. Once the setpoint value has been determined, the electronic control unit commands the actuator using a setpoint value so that the actuator permanently and dynamically works toward achieving the previously defined and/or selected target value. The setpoint may be calculated as a function of torque, force, position or some other parameter. 
         [0011]    The actuator moves the elements of the booster until the sensor emits the selected setpoint value. 
         [0012]    The booster according to the present invention, by acting upon the value of the target signal for the control loop of the booster actuator acts on the clearance at equilibrium, that is to say on the geometric jump S, in order to obtain the desired function (of emergency brake boosting, braking with multiple boost ratios, compensation for variations in mass under driving conditions or the like) and/or the desired braking characteristic (braking with “bite”, gentle braking that is easy to meter, or the like) according to the conditions under which the vehicle is being used, such as the speed at the time of braking, the total mass under driving conditions, the conditions of grip or the behavior of the driver (such as, for example, the speed at which he applies his foot to the brake pedal, the force of application, etc.). 
         [0013]    A main subject of the invention is a device for commanding braking in a motor vehicle, comprising: first moving gear comprising a component that can be driven by the member via which the driver actuates the braking, typically a brake pedal; second moving gear comprising a brake boost actuator driving a force application element; a position sensor that senses the relative position of said first and second moving gear; a processor formulating control setpoints for commanding the brake boost actuator, characterized in that the processor formulates control setpoints for commanding the actuator in such a way as to generate a non-zero offset between the equilibrium positions of said first and second moving gear. 
         [0014]    Another subject of the invention is such a device, characterized in that the processor formulates control setpoints for commanding the actuator in such a way as to cause said offset between the equilibrium position of said first and second moving gear to vary. 
         [0015]    Another subject of the invention is such a device characterized in that it further comprises a reaction device applying a reaction force to said first moving gear and in that the equilibrium position at which the offset between said first and second moving gear is detected by the sensor is an equilibrium position for the reaction force on said first moving gear. 
         [0016]    Another subject of the invention is such a device characterized in that said offset increases the jump with respect to the jump at the position in which there is no offset to the corresponding jump between the component that can be driven by the driver actuating member and the force applying element. 
         [0017]    Another subject of the invention is such a device characterized in that the actuator comprises an electric motor. 
         [0018]    Another subject of the invention is such a device characterized in that it comprises a boost piston driven by the pressure of a hydraulic fluid in a thrust chamber. 
         [0019]    Another subject of the invention is such a device characterized in that it comprises: a hydraulic fluid pressure generator, comprising a variable-volume annular chamber and an annular piston which, on command, is driven by said electric motor; and connecting means for connecting the outlet of the variable-volume annular chamber to the thrust chamber. 
         [0020]    Another subject of the invention is such a device characterized in that it further comprises means for, on command, connecting the hydraulic fluid pressure generating means to one chamber of a master cylinder. 
         [0021]    Another subject of the invention is such a device characterized in that it further comprises means for, on command, hermetically isolating the variable-volume chamber from the thrust chamber. 
         [0022]    Another subject of the invention is such a device characterized in that it further comprises means for, on command, hermetically isolating one chamber of the master cylinder from the brake fluid reservoir. 
         [0023]    Another subject of the invention is such a device characterized in that the processor is capable of formulating setpoints for the actuator in such a way as to cause, during braking, said offset between the equilibrium position for reaction force on said component that can be driven by the actuating member and the position of the force application element of the actuator to vary. 
         [0024]    Another subject of the invention is a method of manufacturing a device for commanding the braking of a motor vehicle, comprising: a step of manufacturing the mechanical and/or hydraulic components of said device; a step of assembling the manufactured components; characterized in that it further comprises a step of programming a processor to allow it to formulate setpoints for commanding an actuator so as to cause an offset between an equilibrium position for reaction force on a component that can be driven by the driver actuating member and the position of the force application element of the actuator to vary. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention will be better understood through the description that follows and the appended figures which are given by way of non-limiting example and among which: 
           [0026]      FIG. 1  is a view in cross section of a first exemplary embodiment of a booster according to the present invention; 
           [0027]      FIG. 2  is a schematic view illustrating the principle employed in the device according to the present invention; 
           [0028]      FIG. 3  is a schematic view in cross section of the preferred exemplary embodiment of the device according to the present invention; 
           [0029]      FIG. 4  is a schematic view in cross section of an alternative form of embodiment of the device of  FIG. 3 ; 
           [0030]      FIG. 5  is a schematic view in cross section of a fourth embodiment of a booster according to the present invention; 
           [0031]      FIG. 6  is a view in cross section of the central element of a fifth exemplary embodiment of a booster according to the present invention; 
           [0032]      FIG. 7  is a view in cross section of a sixth exemplary embodiment of a booster according to the invention; 
           [0033]      FIG. 8  is a schematic view in cross section of a seventh exemplary embodiment of a booster according to the invention; 
           [0034]      FIG. 9  is a view in cross section of a first exemplary embodiment of a sensor that can be used in the booster according to the present invention; 
           [0035]      FIG. 10  is a view in cross section of a second exemplary embodiment of a sensor that can be used in the booster according to the present invention; 
           [0036]      FIG. 11   a  is a view in cross section of a third exemplary embodiment of a sensor that can be used in a booster according to the present invention, in a first position; 
           [0037]      FIG. 11   b  is a similar view of the sensor of  FIG. 11   a , but in a second position; 
           [0038]      FIG. 11   c  is a similar view of the sensor of  FIG. 11   a , but in a third position; 
           [0039]      FIG. 12   a  is a schematic view in cross section of a reaction device in equilibrium that can be used in a booster according to the present invention corresponding to the neutral position of the sensor as illustrated in  FIG. 11   b;    
           [0040]      FIG. 12   b  is a symbolic depiction in signal-processing terms, of the signal of the sensor at equilibrium; 
           [0041]      FIG. 12   c  is a curve representing the master cylinder output pressure P as a function of the input force F applied to the control rod corresponding to the position of the reaction device shown in  FIG. 12   a;    
           [0042]      FIG. 13   a  is a view similar to  FIG. 12   a  for a dynamic equilibrium position of the detector illustrated in  FIG. 11   a;    
           [0043]      FIG. 13   b  is a view similar to  FIG. 12   b  for the position of the reaction device illustrated in  FIG. 13   a;    
           [0044]      FIG. 13   c  is view similar to  FIG. 12   c  for a position of the reaction device illustrated in  FIG. 13   a;    
           [0045]      FIG. 14   a  is a view similar to  FIG. 12   a  for a dynamic equilibrium position of the sensor corresponding to the position illustrated in  FIG. 11   c;    
           [0046]      FIG. 14   b  is a figure similar to  FIG. 12   b  but corresponding to the position of the reaction device as illustrated in  FIG. 14   a;    
           [0047]      FIG. 14   c  is a view similar to  FIG. 12   c  but corresponding to the position of the reaction device as illustrated in  FIG. 14   a;    
           [0048]      FIG. 15  is a set of curves of the master cylinder output pressure P as a function of the force F applied to the control rod for various dynamic equilibrium positions corresponding to various aforementioned relative positions; 
           [0049]      FIG. 16  is a set of curves illustrating the deceleration γ of the braked vehicle equipped with a booster according to the present invention, as a function of the force F applied to the control rod corresponding to the conditions illustrated in  FIG. 15 ; 
           [0050]      FIG. 17  is a set of curves illustrating the various possible behaviors of the system according to the present invention as a function of a variable such as the master cylinder output pressure, the force applied to a brake pedal, the deceleration of the vehicle or the transported load; 
           [0051]      FIG. 18  is a set of curves similar to  FIG. 17  but illustrating the possible change in equilibriums during one and the same braking action in order to obtain unprecedented braking characteristics; 
           [0052]      FIG. 19  is a schematic view in cross section of an eighth exemplary embodiment of a booster according to the present invention; 
           [0053]      FIG. 20  is a schematic view in cross section of a ninth exemplary embodiment of a booster according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    In  FIGS. 1 to 20 , the same references have been used to denote elements that are the same. 
         [0055]      FIG. 1  shows a first embodiment according to the present invention comprising a casing  2 , a rotary electric motor  4  of axis X positioned inside the casing and which is able to drive a ring  12 . In the example depicted, the motor is formed of a stationary electrical element known as a stator secured to the casing  2  and of a rotationally moving electrical element known as a rotor  8  inside the stator. The stator is electrically powered, for example, by an alternator (not depicted). 
         [0056]    The booster is attached to a bulkhead  3  that separates an engine compartment from the passenger compartment of the motor vehicle. 
         [0057]    Because the internal structure of the rotary electric motor is well known to those skilled in the art, it will not be described further. 
         [0058]    The rotor  8  forms a nut of a screw-nut assembly, advantageously of the type comprising balls, positioned inside the casing. The rotor is prevented from translational movement but is able to rotate about the longitudinal axis X, the rotor is held in the booster casing by means of a first and a second set of ball bearings  7  and  9 . 
         [0059]    The screw-nut assembly  10  also comprises a screw formed by the annular ring  12  kept stationary in terms of rotation with respect to the booster casing but able to move translationally with respect to the rotor  8 . 
         [0060]    The rotation of the rotor  8  causes a translational movement of the ring  12  via a first screw thread  12  carried by the interior wall of the rotor, the annular ring for its part being provided on its exterior surface with a second screw thread  16  able to engage with the first screw thread  14 . Advantageously, balls  18  are interposed between the exterior wall of the ring  12  and the interior wall of the cylindrical sleeve that forms the rotor. 
         [0061]    The booster according to the present invention also comprises a boost piston  20  of axis X mounted inside the ring  12 . The boost piston comprises, at a rear first end, a piston shank  22  and, at a front second end, a mount  24  resting via a rear face  26  against a transverse front face  28  of the annular ring  12 . Passing through the boost piston  20  is a longitudinal passage  30  in which a plunger  32  is slidably mounted. 
         [0062]    At a rear first end  34  the plunger  32  accepts a front first end  35  of a control rod  36  and is able via a front second end to come into contact with a first face  38  of a reaction disk  40  made of non-compressible and elastically deformable material such as an elastomer. The front second end of the plunger  37  is also known as the feeler. 
         [0063]    The control rod  36  is connected by a rear second longitudinal end to a brake pedal that can be moved by a driver of a vehicle. 
         [0064]    The reaction disk  40  is arranged in a housing  42  made in the front face of the boost piston so that it bears via a first face  38  against the boost piston by a radially external part. The reaction disk bears via a second face  44  against a rear first end  46  of a push rod  47  intended to transmit the force from the driver and the boost force from the booster to a piston  49  of a master cylinder  48  via a front second end  50 . 
         [0065]    At rest, there is a clearance between the feeler  37  and a central part of the rear face of the reaction disk and this clearance sets the magnitude of the jump of the booster. 
         [0066]    According to the invention and as will be explained hereinafter, the jump can be adjusted dynamically by actuating the motor  4  on command. Thus, the position of first moving gear connected to the brake pedal  1 , typically to the plunger  37  and/or to the control rod  36 , with respect to the second moving gear connected to the piston of the master cylinder  48 , typically with respect to the push rod, relative to the drive piston of the reaction disk  40 , is constantly dynamically adjusted, even when at rest if so desired, during a braking action, by the action of the motor  4 . The clearance or distance known as the geometric jump S in the remainder of this patent, between the feeler  37  and a central part of the rear face of the reaction disk  40  can be kept fixed for one vehicle or vehicle model, or can vary from one braking action to another for the same vehicle or even during one and the same braking action, according to the desired braking characteristics. 
         [0067]    The booster also comprises a means of fixing the plunger with respect to the boost piston, these means  52  are formed by a key substantially perpendicular to the axis X and mounted fixedly on the rear end  34  of the plunger and passing with clearance through a transverse slot made in the piston shank  22 . 
         [0068]    At rest, the transverse ends  58 ′ of the key butt against the booster casing in the embodiment depicted, the rear end of the casing comprises a shoulder  60  against which an annular washer that forms an abutment for the key  54  can rest. 
         [0069]    Sealing means are advantageously provided for sealing between the casing and the exterior surface of the piston shank and connecting the casing and the control rod in such a way as to avoid the ingress of foreign particles liable to disrupt the correct operation of the booster according to the present invention. 
         [0070]    According to the present invention, the booster also comprises means  66  for detecting the relative movement of the boost piston and of the plunger, this detection allowing an electronic control unit to command the actuation of the electric motor, and thereby the movement of the boost piston. 
         [0071]    The means  66  are electrically connected to an electronic control unit (ECU) by a connector  65 . 
         [0072]    The motor  4  receives the control signal from the electronic control unit via the link  100 . 
         [0073]    According to the first exemplary embodiment depicted in  FIGS. 1 and 10 , the means  66  for detecting the relative movement of the boost piston of the plunger comprise an elastic means interposed between the plunger and the boost piston and a force sensor  70 , the elastic means  68  bears via a first end against the plunger and via a second end against the sensor  70 . In the example depicted, the first end of the elastic means  68  bears against the bottom of an axial annular groove of the plunger. The force sensor  70  for its part in the example depicted is of substantially annular shape, secured firmly to the boost piston and surrounding the front end of the plunger. 
         [0074]    In the rest position, the elastic means, which in this example has been depicted as being formed by a cylindrical spring, is preloaded. Thus, the force sensor at rest detects a force applied by the cylindrical spring, this magnitude of the force at rest forms a reference value V for the electronic control unit, as depicted at the point  11 . 
         [0075]    Advantageously, the screw pitch of the screw-nut assembly is reversible, so the boost piston can be returned to the rest position without activating the electric motor. 
         [0076]    A “reversible” screw pitch is understood in the present application to mean a screw pitch that allows the screw to return to the rest position under the sole action of the pressure contained in the master cylinder and of the master cylinder piston return spring. There is no need to rotate the rotor in the opposite direction to the direction that moves the ring towards the master cylinder, known as the pressure rise direction. An irreversible screw pitch is understood in the present application to mean one that requires the rotor to be rotated in the opposite direction to the pressure rise direction in order to return the annular ring to the rest position. 
         [0077]    Quite clearly, use of an elastic means other than a spiral spring is not outside of the scope of the present invention. 
         [0078]    Unlike in the device described in FR 2 860 474, the electronic control unit  5  is not restricted to an automatic control function that tends, in a closed loop, to slave the value of the signal delivered by the connector  65  by the detection means  66  to a value V at rest at the point  11  (typically V at rest is 0). Rather, the electronic control unit  5  may, if necessary or beneficial, and advantageously in a closed loop, apply automatic control to the motor  4  in such a way that the signal, typically the voltage, delivered by the detection means  66  is a negative signal  15 . 1 ,  15 . 2 , etc., corresponding for example to an increase in the jump or, on the other hand, slaved to positive voltage values such as  17 . 1  or  17 . 2 . This automatic control can be performed by autonomous running of the programs in the electronic control unit  5  or, on the other hand, by executing a program in response to a command  19  received by the electronic control unit  5 , for example via a bus such as the CAN bus commonly used in the automotive industry. A vehicle user interface command, such as a push button, a control knob or an input to be selected from a vehicle configuration menu allowing the driver to select the desired braking system behavior can also be connected to an input device connected directly or otherwise, for example at  19 , to the electronic control unit  5 . 
         [0079]    As illustrated in  FIG. 2 , it is clearly understood that the present invention is not restricted to electric brake boosters but covers any booster that comprises an actuator  72  commanded by a control device advantageously an electronic control unit  5 , a reaction device, typically a disk  40 , position detection means  66  or means for detecting the variation in the position of the moving gear connected to the brake pedal and a means of generating pressure, advantageously a master cylinder  48 . 
         [0080]      FIG. 3  shows one exemplary embodiment of a booster according to the present invention, comprising a tandem master cylinder  48  additionally equipped with a thrust chamber  76  which, on command, advantageously from an electronic control unit  5 , receives a fluid, typically brake fluid, under pressure. 
         [0081]    Advantageously, the effective surface area of the thrust chamber  76  is tailored to suit the effective surface area of the primary and/or secondary piston of the master cylinder  48 . 
         [0082]    For example, the effective surface area of the thrust chamber  76  is increased over that of the chambers of the master cylinder if a low pressure (for example limited to 10 7  Pa) of the source of pressurized brake fluid is to be compensated for. However, such a ratio of surface areas carries the risk of causing the brake pedal  1  to move in active modes. 
         [0083]    When said surface areas are equal, the saturation pressure, that is to say the maximum pressure supplied by the high-pressure source is equal to the pressure generated by the boost function on the output side of the master cylinder. The pedal  1  remains immobile during the active modes. 
         [0084]    For effective surface areas of the thrust chamber  76  which are lower than those of the master cylinder pistons, the volume of fluid that has to be supplied to the chamber  76  for a given braking value is decreased, making it possible to limit the output of the pump, to reduce the volume of the accumulator and/or to improve the dynamic response of the braking action, that is to say to reduce the response time of the braking system. 
         [0085]    In the example advantageously illustrated, the booster according to the present invention comprises a hydraulic piston  78  the rear face of which delimits the thrust chamber  76  and the front face of which is positioned in a bore filled with a compressible fluid, typically air, advantageously vented to the atmosphere via a line  80 . In the preferred embodiment illustrated, a recess in the hydraulic piston  78  accommodates the reaction disk  40  on the front face of which there bears a push rod  47 . The rear face of the accommodating housing in the reaction disk  40  comprises a shoulder so that the corresponding section of the reaction disk can be pushed by the hydraulic piston  78 , and there is a central opening to accommodate the anterior part of the plunger  37 , the ratio of surface areas between said shoulder and said opening determining the default boost ratio, at the point  11 , of the booster. 
         [0086]    In the advantageous example illustrated, the means for generating the feed pressure in the thrust chamber  76  comprise a master cylinder  82  comprising a variable-volume chamber  84  in which the pressure of the brake fluid is increased by a piston driven, on command  100  by a motor  88 , advantageously an electric motor. 
         [0087]    In the advantageous example illustrated, the chamber  84  is an annular chamber connected by a line  90  to the thrust chamber  76 . Advantageously, the motor is a stepping motor and drives the piston  86  via a ball screw. 
         [0088]    In the advantageous example illustrated, the piston  86  comprises, at least at one of its axial ends, a hydraulic seal capable of withstanding the control pressures, preferably, as illustrated, a seal of the cup type. 
         [0089]    Advantageously, the booster according to the present invention further comprises an electrically operated valve  94  that can, on command, hermetically seal a line  96  connecting the chamber  84  to the master cylinder  48 . In the advantageous example illustrated, the line  96  opens, at the master cylinder end, between two cups which, in a known manner, delimit a master cylinder resupply chamber. This chamber is also connected to a brake fluid reservoir  98 . Furthermore, at rest, the resupply chamber is connected by openings made in the primary piston to the primary chamber of the master cylinder  48 . On the other hand, when the primary piston advances, the openings move beyond the anterior cup allowing the pressure in the braking circuit to rise. The electrically operated valve  94  is able, if the motor  88  fails during the course of a braking action, to release the pressure of the chamber  84  into the reservoir  98  and thus, in the event that the motor  88  fails, avoid undesired braking. Likewise, it should be noted that, in the absence of boost assistance following failure of the motor  88 , thrust on the control rod drives the push rod  47  directly without the need to drive the motor  88 . 
         [0090]      FIG. 4  shows the preferred exemplary embodiment of the booster according to the present invention which, apart form the elements of the booster of  FIG. 3 , comprises a second electrically operated valve  102  which, on command, isolates the thrust chamber  76  from the chamber  84  of the master cylinder  82 . Thus it is possible to maintain constant hydraulic brake pressure independently of action of the motor. This may be beneficial, for example, for constant pressures on the brake pedal, for example when stopped at a red light, stopped for a prolonged length of time, or driving downhill with the brakes constantly applied. Thus, in such instances, there is no need to actuate the motor  88 . The electrical power consumption and wear of the motor are thus reduced. The second electrically operated valve  102  is particularly beneficial if reversible screws are being used, that is to say screws that can be turned by a variation in pressure in the motor chamber  76 . 
         [0091]    Advantageously, the booster according to the present invention further comprises a third electrically operated valve  103  which, on command, isolates the primary chamber of the master cylinder  48  from the brake fluid reservoir  98 . It is thus possible to pre-fill the braking circuit through the master cylinder by opening the electrically operated valve  94  and closing the valve  103  so as to prevent the pressure supplied to the primary chamber from escaping to the reservoir. It should be noted that the pre-filling of the brakes is carried out with no forward movement of the control rod  36 , or therefore of the brake pedal  1 . Likewise, the combination whereby the electrically operated valves  94  are open and the electrically operated valve  103  is closed allows active braking modes, that is to say modes at the command of the electronic control unit  5 , to be implemented without any need for action on the part of the driver and without any movement of the pedal  1 . It should be noted that the secondary piston transmits to the secondary chamber the pressure that is in the primary chamber, notably in active braking scenarios. 
         [0092]    The pre-filling of the brakes may be highly beneficial in shortening braking distances and/or in allowing use of hydraulic braking with increased retreating of the piston which exhibits zero and/or at the very least reduced, residual (undesired) braking torque. 
         [0093]    Furthermore, the electrically operated valve  103  or another means of hermetic isolation, on command, can be actuated in such a way as to isolate at least one of the chambers of the master cylinder  48 , typically the primary chamber, so as, for example, to reduce the dead travel at the time of actuation of the brakes, and preferably before the resupply holes in the primary piston have traveled beyond the front cup of the primary chamber of the master cylinder or, if an abnormally high temperature has been detected during a braking action that could, were the braking action to be released, cause the brake fluid to boil. However, upon complete release of the brakes, that is to say where no pressure is applied to the brake pedal, possibly after a time delay has elapsed, the electrically operated valve  103  is re-opened so as to avoid undesired braking. 
         [0094]    It must be clearly understood that, as illustrated in  FIG. 5 , use of a pedal feel simulator  104  associated with position detection means  66  belonging to an electronic control unit  5  used to command active braking means is not outside the scope of the present invention. 
         [0095]    In the example illustrated in  FIG. 5 , the simulator comprises two hydraulic chambers connected by lines, the boost and braking devices being analogous to those of  FIG. 3 . As an alterative, the electric motor  88 , on command, causes the advance movement of a piston  86  of a master cylinder that is not necessarily annular for supplying a thrust chamber  76  with pressurized brake fluid. 
         [0096]    Use of a simulator makes it possible, at the expense of an increase in complexity of the system and of its cost, for the control setpoint generated in the simulator to be completely dissociated from the pressure actually generated in the brake. Doing this may prove extremely beneficial in the case of collaboration between various braking systems, such as, for example, the regenerative braking system used in hybrid vehicles which comprises not only a combustion engine but also an electric motor both capable, under braking, to behave like an energy recuperating generator. 
         [0097]      FIG. 6  shows the central part of a vacuum pneumatic brake booster according to the present invention. The pneumatic booster of  FIG. 6  comprises, contained inside a casing that has not been depicted, a front chamber  106  connected to a vacuum and a rear chamber  108  that can be connected, at the command of a three-way valve, to atmospheric pressure. The three-way valve may be commanded, not only by the control rod  36 , but also by an actuator  110  that receives a control signal  100  from the electronic control unit  5 . 
         [0098]    Advantageously, the actuator is an electromagnet. 
         [0099]      FIG. 7  shows an exemplary embodiment of a hydraulic booster according to the present invention, comprising a hydraulic thrust chamber  76  supplied with pressurized fluid by a vacuum pneumatic booster the filling of the rear chamber  108  of which is performed by an electrically operated valve  114  commanded by the electronic control unit  5 . 
         [0100]      FIG. 8  shows an exemplary embodiment of a booster according to the present invention comprising a thrust chamber  76  supplied, at the command of the electronic control unit  5 , by a pump  116 , advantageously via a hydraulic circuit  118  that comprises, for example, a valve and an accumulator. Use may be made of a dedicated, advantageously electric, pump  116  or, on the other hand, use may be made of a pump already present in the motor vehicle such as a hydraulic power steering pump or an electronic stability program (ESP) pump. 
         [0101]      FIG. 9  shows a first exemplary embodiment of the means  66  of detecting the relative position of the moving gear comprising the brake pedal  1  with respect to a second moving gear connected to the piston of the master cylinder in the example of  FIG. 9 , the first moving gear being equipped with a magnet  120  positioned facing a magnetic field detector  122 , for example a Hall effect detector. Advantageously, the magnet  120  is an annular magnet and the detector  122  is a proportional detector. The axial movement along the axis X causes the magnetic field at the detector  122  and therefore the voltage  65  delivered by this detector, to vary. Advantageously, the arrangement of north and south poles on the magnet  120  is axially along the axis X. 
         [0102]      FIG. 10  shows, on a larger scale, the detector used in the device of  FIG. 1  and which comprises a force sensor  70  compressed by a helical spring  68 . Advantageously, the spring has a constant spring rate k so that the force F applied by this spring to the sensor is proportional to the movement of the plunger  32  a shoulder of which compresses the spring. 
         [0103]      FIGS. 11   a ,  11   b  and  11   c  show the preferred exemplary embodiment of the detection means  66  comprising an elastic washer  128  bearing, on its surface, one or more strain gauges, for example circumferential and/or radial strain gauges  130 . The washer  128  comprises means of anchorage on a first moving gear and drive means connected to the second moving gear. Advantageously, the washer  128  comprises peripheral means of anchorage on the moving gear driven by the booster actuator according to the present invention. Typically, the periphery of the washer  128  is anchored in a bore of the piston. The drive means of the radially internal edge of the washer  128  are advantageously carried by the plunger  32 . Thus, the means  66  of  FIG. 11  are able to detect the relative movement of the first moving gear connected to the brake pedal with respect to the second moving gear driven by the actuator. 
         [0104]      FIG. 11   a  depicts the washer deformed forward, that is to say that the plunger has taken the lead over the piston. In other words, the value of the jump has been reduced in the position illustrated in  FIG. 11   a , which corresponds to the point  17 . i  ( 17 . 1 ,  17 . 2 , etc.) the voltage V delivered by the strain gauge being positive. 
         [0105]    In  FIG. 11   b  the washer  128  is not deformed and this corresponds to the point  11 , the jump being at its nominal value and the voltage V being zero. It should be noted that this is the only position accessible during operation of the motor  4  of the booster described in patent FR 2 860 474. 
         [0106]    In  FIG. 11   c , the washer is deformed to the rear, the strain gauge  130  delivering a signal  65  that has a negative voltage corresponding to the point  15 . i , ( 15 . 1 ,  15 . 2 , etc.) with the piston having taken the lead over the plunger and the jump increased. 
         [0107]    Of course, reversing the polarity of the strain gauge  130  or changing the position of the origin is not outside of the scope of the present invention. 
         [0108]    Likewise, use of an intelligent sensor, of a sensor that delivers a numerical value, a pulse width modulator (PWM) or the like is not outside the scope of the present invention. 
         [0109]      FIG. 12   a  shows the control module of a booster according to the present invention in a neutral position in which the geometric jump S, that is to say the distance between the anterior face of the feeler  32  and the rear face of the reaction disk measured along the axis X is determined by the geometry of the components used. This is a neutral position in which the washer  128  is in the position illustrated in  FIG. 11   b.    
         [0110]      FIG. 12   b  illustrates the position of the control signal  100  delivered by the electronic control unit to the actuator at the point  11 . This symbolic depiction indicates that, on the one hand, the washer  128  is not deformed and that therefore the strain gauge  130  delivers a zero signal even when the piston is being controlled by the actuator.  FIG. 12   c  shows a curve  132  illustrating the output pressure P of the master cylinder as a function of the force F applied by the driver to the control rod  36  of a booster according to the present invention, of which equilibrium afforded by the actuator corresponds to the position illustrated in  FIG. 12   a.    
         [0111]    A first portion  134  at zero pressure corresponds to the instigating force. 
         [0112]    A second portion Sp which is substantially vertical corresponds to a rise in pressure at constant force at the start of braking. The pressure jump Sp is connected to an inclined straight portion the gradient of which corresponds to the boost ratio of the booster. The portion  136  is connected to a portion  138  of shallower gradient corresponding to saturation of the booster, that is to say the point where the booster is providing the maximum force of which it is capable, the increase in pressure resulting only from the increase in the force applied to the control rod  36  via the brake pedal. 
         [0113]      FIG. 13   a  shows the device of  FIG. 12   a  in which the first moving gear comprising the plunger  37  has taken the lead over the piston. The result of this is that, firstly, the washer  128  is deformed in a similar way to the way illustrated in  FIG. 11   a  and that secondly, the geometric value of the jump S is reduced by comparison with the value of the jump S of the device kept in equilibrium in  FIG. 12   a.    
         [0114]    This fact is symbolized in  FIG. 13   b  by the fact that the strain gauge  130  is delivering a positive voltage V+ corresponding to the flexing of the washer  128 . It should be noted that, depending on the type of braking desired, the actuator  72 , typically the electric motor  4 , can keep the position of  FIG. 13   a  constant or, on the other hand, cause the positional offset of the two moving gears and therefore the direction and amplitude of deformation of the washer  128  to vary. 
         [0115]      FIG. 13   c  shows that the pressure jump Sp has decreased on curve  132 , changing the way in which the vehicle behaves under braking. 
         [0116]    The configuration of  FIG. 13  may, for example, make it possible to reduce the bite of the brakes both in normal use and, for example, when the vehicle is transporting a light weight or if somebody wishes smooth and/or gentle automatic braking or fine control over braking, for example when actuating an automatic parking brake. 
         [0117]      FIG. 14   a  illustrates the device of  FIG. 12   a  with a washer  128  deformed toward the rear illustrated in  FIG. 11   c  in so far as the second moving gear driven by the actuator  72 , typically the motor  4 , has taken a lead over the first moving gear comprising the plunger  37 . 
         [0118]    This results in an increase in pressure jump Sp of which the extreme example illustrated in  FIG. 14   c  corresponds to a vertical line Sp directly connecting a zero pressure to a saturation pressure without any inclined segment  136 . In  FIG. 14   b , the value of the signal is illustrated at the point  15 . i.    
         [0119]    This type of behavior may prove particularly beneficial in the case of emergency braking or rapid braking allowing a driver, even a fearful one, who dare not press the pedal too hard or who is physically weak, to obtain a short stopping distance and/or a substantial deceleration. Thus control of the actuator  72 , typically of the motor  4 , makes it possible to obtain an emergency braking or brake assist function. 
         [0120]      FIG. 15  shows three curves of the pressure P available on the output side of the master cylinder as a function of the force F applied by the driver for a possible use of the booster according to the present invention with, for example, a command that includes a compensation  100 , emitted by the electronic control unit  5 , for the load of the vehicle. Curve  132 . 1  corresponds to a zero or negligible jump corresponding to a position extending slightly beyond the one illustrated in  FIG. 13   a . Curve  132 . 1  corresponds, for example, to the behavior desired and obtained by the booster according to the present invention, for a vehicle with a payload lower than the normal customary payload of the vehicle, for example a scenario in which the payload of the vehicle consists mainly of the driver himself. Curve  132 . 2  corresponds to the neutral position illustrated in  FIG. 12   a . Curve  132 . 2  corresponds to a normally laden vehicle. Curve  132 . 3  depicts the case of an increased jump (but not as increased as the jump illustrated in  FIG. 14   a ). Curve  132 . 3  corresponds to a vehicle transporting a load higher than the normal payload. The load transported by the vehicle or, more specifically, the moving mass, is determined in the known way, for example by a vehicle stability control system known in the art as an ESP system and/or an accelerometer. 
         [0121]    Thus, the three curves have segments  136  that are parallel to one another and the gradient of which corresponds to the boost ratio. It is interesting to compare these curves with the sets of curves  138 . 1 ,  138 . 2  and  138 . 3  of  FIG. 16  which illustrates the deceleration γ as a function of the force F. Curve  138 . 1  in  FIG. 16  corresponds to the case of curve  132 . 1  of  FIG. 15 . Curve  138 . 2  of  FIG. 16  corresponds to curve  132 . 2  of  FIG. 15 . Curve  138 . 3  of  FIG. 16  corresponds to curve  132 . 3  of  FIG. 15 . It will be noted first of all that it is advantageous to obtain a deceleration jump Sγ which is constant for all three curves  138 . 
         [0122]    In other words, the deceleration at the end of the jump γ is the same for all three curves. By contrast, after the jumps, the gradients of the curves  138 . 1 ,  138 . 2  and  138 . 3  increase to meet the saturation curves  140 . 1 ,  140 . 2  and  140 . 3  respectively, which are mutually parallel. Curve  140 . 3  is above curve  140 . 2  itself above curve  140 . 1 . It should be noted that the deceleration saturation curves take account of the total force applied both by the brake boosters and by the driver. It can be seen better in  FIG. 16  that the brake behavior and feel are completely different according to the relative positions of the two sets of moving gear. Notably, for a lower pressure jump (curve  132 . 1 ) the driver can be brought to a higher saturation curve ( 140 . 1 ) and therefore to a shorter stopping distance and/or to a stopping distance that remains substantially unchanged even for a higher payload, that is to say a higher moving mass. 
         [0123]      FIG. 17  illustrates a set of curves of pressure P as a function of force F for various settings of the system jump according to the present invention ranging, for example, from a curve  132 . 1  that optimizes braking for a hydraulic pressure of 2×10 6  Pa, a curve  132 . 2  that optimizes braking for a hydraulic pressure of 4×10 6  Pa, a curve  132 . 3  that optimizes braking for a hydraulic pressure of 4×10 6  Pa, a curve  132 . 4  that optimizes braking for a hydraulic pressure of 8×10 6  Pa, to arrive at a curve  132 . 5  corresponding, for example, to 10 7  Pa. In addition, as illustrated in  FIG. 18 , the changes to be offset between the sets of moving gear may evolve over the course of one and the same braking action as the driver gradually presses harder on the brake and/or as a function of the pressure P and/or of the deceleration γ. It is, for example, possible to switch from the curve  132 . 1  to the curve  132 . 2 ,  132 . 3 ,  132 . 4  toward the curve  132 . 5  at the time of saturation. In  FIG. 18 , the points that correspond to the pair of values (F, P) for pressures of 2×10 6  Pa, 4×10 6  Pa, 6×10 6  Pa, 8×10 6  Pa and 10 7  Pa bear the respective references  144 . 1 ,  144 . 2 ,  144 . 3 ,  144 . 4  and  144 . 5 . The straight-line segment connecting said points  144 . 1  to  144 . 5  bears the references  146  and corresponds to the possible behavior of a braking system according to the present invention, a careful choice of the points  144 . i  ( 144 . 1 ,  144 . 2 , . . . ,  144 . 5 ) making it possible, if that is desired, to obtain braking system behavior that would be impossible to achieve with any device of known type. It is possible to increase and/or decrease a boost ratio, linearly or otherwise, to describe a curve such as an arc of a circle, of the sinusoidal, hyperbolic, or some other type. 
         [0124]    Further, it is possible to reduce the price of the booster according to the present invention by tolerating, in industrial production, a wider spread on geometric jumps while at the same time providing compensation for this spread by a correction made by the motor  4  and/or the actuator  72 . Likewise, according to the present invention, it is possible, by using the actuator, on a command  100  from the electronic control unit  5 , to reduce the tolerance on the jumps that can be achieved in manufacture. Likewise, it is possible when optimizing a braking system, to carry out tests on the various pedal feels without modifying the device, solely by changing the characteristics of the control loop for the automatic control of the motor  4  and/or of the actuator  72 . These advantages can be added to and/or combined with the advantages already mentioned, namely the possibility of achieving a variable jump, of varying the boost ratio, of obtaining double or multiple boost ratios, of having boost ratios that are able to vary nonlinearly with the force, of affording emergency brake assist function, of compensating for braking as a function of the load carried by the vehicle, of taking multiple braking elements (hydraulic braking plus regenerative braking) into consideration with a corresponding deceleration to the braking setpoint (force F applied to the pedal  1 ) independently of the respective contributions by the hydraulic and regenerative braking system and/or the change in pedal feel, notably the disappearance of the hard pedal feel during active braking mode such as those generated by the automatic braking comfort devices for example those of the ACC type. 
         [0125]    Advantageously, the electronic control unit  5  may estimate the type of pedal feel desired by the driver or drivers and adapt the pedal feel to the desired pedal feel. 
         [0126]      FIG. 19  shows one exemplary embodiment of a booster according to the present invention comprising a hydraulic unit  146  comprising a pump  116  and a hydraulic control circuit  118  comprising, for example, a first electrically operated valve  118 . 1  for removing fluid from the thrust chamber  76  and a second electrically operated valve  118 . 2  for supplying pressurized hydraulic fluid to said thrust chamber  76 . Advantageously, the valves  118 . 1  and  118 . 2  are on/off valves that can be controlled either continuously or, advantageously, by pulse width modulation (PWM). 
         [0127]    Advantageously, the high-pressure outlet of the pump  116  is connected to an accumulator  148  allowing the pump  116  to be switched off when its operation is not required. Advantageously, a pressure sensor  150  measures the pressure available at the outlet of the pump  116 /of the accumulator  148 . Advantageously, the pressure sensor  150  is connected to a control device that controls a motor of the pump  116 , and by a link  19  to the electronic control unit  5 . Of course, the use of other pressure sensors, for example in the primary and secondary braking circuit, connected to the electronic control unit  5  and providing pressure control, is not outside of the scope of the present invention. 
         [0128]    In the example illustrated in  FIG. 19 , the line  80  is connected to the reservoir  98  in such a way as to fill the intermediate chamber lying between the chamber  76  and the primary chamber of the master cylinder, at atmospheric pressure. Thus, the various sealing elements, typically the cups, are immersed in brake fluid on their two opposing sides. 
         [0129]    The device of  FIG. 19  operates in substantially the same way as the device of  FIG. 8 . 
         [0130]    However, the use of the hermetic unit  146 , already available in an electronic stability system (ESP) on a modern vehicle allows the device according to the invention to be installed at only a modest additional cost. 
         [0131]    In the preferred example illustrated, the low-pressure inlet of the pump  116  is connected by a line  152  to the reservoir  98 . Each of the chambers of the tandem master cylinder  48  is connected to said reservoir  98  by a line. 
         [0132]      FIG. 20  shows an alternative form of embodiment of the device according to the present invention of  FIG. 19  in which the hydraulic control circuit  118  further comprises a third electrically operated valve  118 . 3  which, on command, connects a pressure source directly or indirectly to the primary chamber of the master cylinder  48 . 
         [0133]    Upon a variation in the position of the brake pedal  1 , corresponding to a variation in the braking setpoint, for example an application of braking, an increase in the braking, a reduction in the braking, or the braking coming to an end, the sensor  66  delivers a corresponding signal  65  to the electronic control unit  5 . The electronic control unit  5  formulates a setpoint for the variation in brake boosting. When the matter is one of an increase in braking, the electrically operated valve  118 . 2  is opened until the pressure in the thrust chamber  76  displaces the hydraulic piston  78  until the sensor  66  delivers a signal  65  corresponding to the desired offset between the first and the second sets of moving gear. When this value is reached, the valve  118 . 2  hermetically isolates the high-pressure stage of the hydraulic unit  146 . During the supply of pressurized brake fluid to the thrust chamber  76 , the valve  118 . 1  connected to the low-pressure stage of the hydraulic unit  146  is closed. 
         [0134]    During braking at a constant level, the two valves  118 . 1  and  118 . 2  are closed. Thus, constant braking does not consume high-pressure brake fluid. 
         [0135]    For brake release, the electronic control unit  5  closes the valve  118 . 2  and opens the valve  118 . 1  until the pressure in the thrust chamber  76  creates an offset between the first and second sets of moving gear corresponding to the desired setpoint value. 
         [0136]    In the absence of any braking, the electrically operated valve  118 . 1  is opened so as to ensure that atmospheric pressure obtains in the thrust chamber  76  while the electrically operated valve  118 . 2  is closed. 
         [0137]    Furthermore, it is advantageous for the primary chamber of the master cylinder  48  not to be connected to the reservoir  98 , resupply being afforded by the electrically operated valve  118 . 3 . Thus (unlike in the example illustrated), it is possible to dispense with the cup and the resupply holes in the primary piston of the master cylinder  48 . 
         [0138]    Advantageously, the hydraulic unit  146  further comprises a second pressure sensor  152  that measures the pressure delivered to the thrust chamber  76 . 
         [0139]    Advantageously, as in the previous cases, the effective cross-sectional area of the thrust chamber  76  is equal to the effective cross-sectional area of the primary piston and/or of the secondary piston of the master cylinder  48 . In the example advantageously illustrated, the valve  118 . 3 , on command  100 , connects the high-pressure stage of the hydraulic unit  146  to the primary chamber of the master cylinder  48 . 
         [0140]    The opening of the valve  118 . 3 , at the command  100  of the electronic control unit  5 , brings about the pre-filling and/or the filling of the primary chamber of the master cylinder  48  allowing the active modes to operate, that is to say without the need for the pedal  1  of the braking system to be depressed, for example for automatic braking at the command of a radar (ACC), parking braking or the like. 
         [0141]    The increase in pressure in the primary cylinder of the master cylinder  48  pushes on the secondary piston which, in turn, causes the rise in pressure in the secondary circuit. 
         [0142]    It should be noted that the fact that the effective cross-sectional areas of the primary piston and of the thrust chamber  76  are equal or near-equal means that high-pressure brake fluid can be supplied to the brakes without the pedal  1  being depressed and without having any need to resort to a simulator (unlike the case illustrated in  FIG. 16 ). In addition, the absence of any connection between the primary chamber of the master cylinder  48  and the reservoir  98  means that one single valve  118 . 3  can be used to perform the active mode and/or the pre-filling of the brakes (without the need for a valve  103 ). 
         [0143]    Of course the various elements illustrated in the various figures of the present patent can be combined without departing from the scope of the present invention. 
         [0144]    The invention applies notably to the automotive industry. 
         [0145]    The invention applies mainly to the braking industry.
   ( 2 ) casing   ( 12 ) ring (annular)   ( 3 ) bulkhead   ( 4 ) rotary electric motor   ( 8 ) rotor   ( 7 ) first set of ball bearings   ( 9 ) second set of ball bearings   ( 10 ) screw-nut assembly   ( 12 ) annular ring   ( 14 ) first screw thread   ( 16 ) second screw thread   ( 18 ) balls   ( 20 ) boost piston   ( 22 ) piston shank   ( 24 ) mount   ( 26 ) rear face   ( 28 ) transverse front face (of the annular ring  12 )   ( 30 ) longitudinal passage   ( 32 ) plunger   ( 34 ) rear first end (of a plunger)   ( 35 ) front first end (of a control rod)   ( 36 ) control rod   ( 37 ) plunger   ( 38 ) first face (of a reaction disk)   ( 40 ) reaction disk   ( 42 ) housing   ( 44 ) second face (of a reaction disk)   ( 46 ) rear first end (of a push rod)   ( 47 ) push rod   ( 48 ) master cylinder   ( 49 ) piston   ( 50 ) front second end (of the piston)   ( 52 ) means of attachment of the plunger   ( 54 ) key   ( 58 ′) transverse ends of the key   ( 60 ) shoulder (of the rear end of the shoulder)   ( 65 ) connector   ( 66 ) means of detection   ( 68 ) elastic means   ( 70 ) force sensor   ( 72 ) actuator   ( 76 ) thrust chamber   ( 78 ) hydraulic piston   ( 80 ) line   ( 82 ) master cylinder for supplying the thrust chamber   ( 84 ) chamber   ( 86 ) piston   ( 88 ) motor   ( 100 ) command   ( 90 ) line   ( 92 ) seal   ( 94 ) electrically operated valve   ( 96 ) line   ( 98 ) reservoir   ( 102 ) electrically operated valve   ( 104 ) simulator   ( 106 ) front chamber   ( 108 ) rear chamber   ( 110 ) actuator   ( 112 ) pneumatic booster   ( 114 ) electrically operated valve   ( 116 ) pump   ( 118 ) hydraulic circuit   ( 120 ) magnet   ( 122 ) magnetic field detector   ( 128 ) elastic washer   ( 130 ) strain gauge   ( 132 ) curve P=f(F)   ( 134 ) functional clearance   ( 136 ) segment prior to saturation   ( 138 ) curve γ=f(F)   ( 140 ) deceleration saturation   ( 142 ) points   ( 144 ) curve   F=force   P=pressure   S=geometric jump   Sp=pressure jump   Sγ=deceleration jump