Abstract:
The instant disclosure describes a braking system for braking at least a first wheel of a motor vehicle comprising a first brake, a hydraulic circuit for controlling the first brake and a first electric motor for controlling the first brake, which brake and motor can be actuated at least partially simultaneously using one and the same actuating member.

Description:
BACKGROUND 
       [0001]    The present description relates to a braking system of a vehicle, particularly an automobile vehicle, comprising a brake-assist device. 
       DISCUSSION OF THE RELATED ART 
       [0002]    In most conventional vehicles, the vehicle wheel braking system comprises, for each wheel, a drum or disk brake controlled by a hydraulic circuit. On older vehicles, the hydraulic circuit comprises a master cylinder directly controlled by the brake pedal. The braking force applied by each brake is then directly linked to the force exerted by the driver on the brake pedal. 
         [0003]    On more recent vehicles, a brake-assist device is provided between the brake pedal and the master cylinder to amplify the force exerted by the driver on the brake pedal. The brake-assist device may use a source of additional energy, for example, pneumatic, which adds to the energy provided by the driver when pressing on the brake pedal. As an example, the brake-assist device may comprise a vacuum booster, for example, of Mastervac type, which requires a depression source for its operation. The pneumatic power source may correspond to the depression in the inlet line of a gasoline motor or to the depression provided by a vacuum pump, for example, for a vehicle comprising a diesel-type motor or for an electric vehicle. 
       SUMMARY 
       [0004]    Thus, an embodiment provides a braking system for at least one first wheel of a motor vehicle comprising a first brake, a hydraulic circuit for controlling the first brake and a first electric motor for controlling the first brake which can be at least partly simultaneously actuated by a same actuation member. 
         [0005]    According to an embodiment, the system comprises a sensor capable of providing a signal representative of the driver&#39;s action on the actuation member, a processing unit capable of providing a set point value from said signal, the first electric motor being controlled based on said set point value. 
         [0006]    According to an embodiment, the first brake is hydraulically controlled and mechanically controlled, the hydraulic circuit being connected to the hydraulic control system of the first brake and the first electric motor being connected to the mechanical control system of the first brake. 
         [0007]    According to an embodiment, the hydraulic circuit comprises a master cylinder connected to the hydraulic control system of the first brake by at least one pipe containing a brake fluid, the braking system comprising a connection mechanism connecting the actuation member to at least one piston of the master cylinder, the connection mechanism comprising no servo-brake. 
         [0008]    According to an embodiment, the system comprises a second hydraulically controlled and mechanically controlled brake, the hydraulic circuit being connected to the hydraulic control system of the second brake. 
         [0009]    According to an embodiment, the first motor is further connected to the mechanical control system of the second brake. 
         [0010]    According to an embodiment, the system further comprises a second electric motor connected to the mechanical control system of the second brake and controlled by the actuation member at least partly simultaneously with the hydraulic circuit. 
         [0011]    According to an embodiment, the system comprises a third hydraulically controlled and mechanically controlled brake, the hydraulic circuit being connected to the hydraulic control system of the third brake. 
         [0012]    According to an embodiment, the first motor is further connected to the hydraulic control system of the third brake. 
         [0013]    According to an embodiment, the system further comprises a third electric motor connected to the mechanical control system of the third brake and controlled by the actuation member at least partly simultaneously with the hydraulic circuit. 
         [0014]    According to an embodiment, the system comprises a fourth hydraulically controlled and mechanically controlled brake, the hydraulic circuit being connected to the hydraulic control system of the fourth brake. 
         [0015]    According to an embodiment, the first motor is further connected to the hydraulic control system of the fourth brake. 
         [0016]    According to an embodiment, the system further comprises a fourth electric motor connected to the mechanical control system of the fourth brake and controlled by the actuation member at least partly simultaneously with the hydraulic circuit. 
         [0017]    An embodiment also provides a vehicle comprising at least one wheel and a system for braking said wheel as previously defined. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which: 
           [0019]      FIG. 1  schematically shows a conventional example of a braking system; 
           [0020]      FIG. 2  schematically illustrates an embodiment of a braking system; 
           [0021]      FIG. 3  schematically shows an example of a disk brake; 
           [0022]      FIG. 4  schematically shows an example of a drum brake; and 
           [0023]      FIGS. 5 to 8  show embodiments of braking systems. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    For clarity, the same elements have been designated with the same reference numerals in the various drawings and, further, the various drawings are not to scale. Further, only those elements which are useful to the understanding of the present description have been shown and will be described. In particular, the structure of the master cylinder of the hydraulic circuit of a braking system has not been described in detail. In the following description, unless otherwise indicated, terms “substantially”, “approximately”, and “in the order of” mean “to within 10%”. 
         [0025]      FIG. 1  shows an example of braking system  10 . System  10  comprises a front left brake  12 , a front right brake  14 , a rear left brake  16 , and a rear right brake  18  fitting the two front wheels and the two back wheels of the vehicle. Brakes  12 ,  14 ,  16 , and  18  may be disk or drum brakes. Brakes  12 ,  14 ,  16 , and  18  are controlled by a hydraulic circuit containing a brake fluid. 
         [0026]    The hydraulic circuit comprises a master cylinder  20  connected to front left brake  12  by a pipe  21 , to front right brake  14  by a pipe  22 , to rear left brake  16  by a pipe  23 , and to rear right brake  18  by a pipe  24 . Master cylinder  20  comprises one or a plurality of pistons, not shown, capable of being displaced by a rod  25 . A displacement of rod  25  results in a displacement of the pistons in master cylinder  20 , which causes a variation of the hydraulic pressure in brakes  12  to  18 . A pressure regulation device  26 , or hydraulic corrector, may be provided on ducts  23  and  24  so that the hydraulic pressure in rear brakes  16 ,  18  is lower than the hydraulic pressure in front brakes  12 ,  14 . 
         [0027]    Master cylinder  20  is actuated by brake pedal  27  of the vehicle via a brake-assist device  28 . The driver&#39;s action on brake pedal  27  causes the displacement of a push rod  29  which controls brake-assist device  28 . Brake-assist device  28  applies an effort to rod  25 , which corresponds to the effort exerted by the driver on brake pedal  27  multiplied by an amplification factor. 
         [0028]    When the driver presses on brake pedal  27 , which is illustrated by arrow F, rod  25  is displaced by brake-assist device  28 . This causes a displacement of the pistons in master cylinder  20  and causes a pressure rise of the brake fluid in pipes  21 ,  22 ,  23 , and  24 , thus actuating brakes  12 ,  14 ,  16 , and  18 . 
         [0029]    A disadvantage of previously-described braking system  10  is that brake-assist device  28  and pressure regulation device  26  occupy a significant volume. Further, the costs of manufacturing and maintenance of brake-assist device  28  and of pressure regulation device  26  are generally high. Further, the operation of assistance device  28  may require the presence of a vacuum pump, which may also be bulky and expensive. 
         [0030]    An object of an embodiment is to decrease the volume and the number of parts of the hydraulic control circuit of the brakes of a braking system. 
         [0031]    Another object of an embodiment is to suppress the hydraulic and/or pneumatic brake-assist device between the brake pedal and the master cylinder. 
         [0032]      FIG. 2  illustrates the operating principle of an embodiment of a braking system  30 . In  FIG. 2 , for simplification, only brake  18  is shown. 
         [0033]    According to this embodiment, push rod  29  driven by brake pedal  27  is directly connected to the pistons of master cylinder  20 . There thus is no hydraulic and/or pneumatic brake-assist device interposed between push rod  29  and master cylinder  20 . 
         [0034]    Braking system  30  further comprises a brake-assist device  32 . Device  32  comprises a sensor  34  and an electromagnetic brake-assist system  36  connected to sensor  34  and to brake  18 . 
         [0035]    Sensor  34  provides a signal S which is representative of the driver&#39;s action on pedal  27 . Sensor  34  may be a sensor measuring the displacement of push rod  29  or the angular displacement of brake pedal  27 , a sensor measuring the force exerted by the driver on brake pedal  27  or the force exerted by brake pedal  27  on push rod  29  or a sensor of the hydraulic pressure in master cylinder  20 . 
         [0036]    System  36  comprises:
       a processing unit  38  receiving signal S;   a control unit  40 ;   an electric motor  42  controlled by control unit  40 ;   a drive mechanism  44  driven by motor  42 ; and   a mechanical connection element  46 , for example, a cable, connecting drive mechanism  44  to brake  18 .       
 
         [0042]    Brake  18  may be controlled in two ways: by a hydraulic control or by a mechanical control. This is true for most current brakes, particularly disk or drum brakes, which generally comprise, in addition to the hydraulic control, a cable control conventionally used to achieve a parking brake function. In this case, connection element  46  of assistance device  32  is connected to the cable control system of brake  18 . 
         [0043]    Processing unit  38  for example comprises a microcontroller. Processing unit  38  may further comprise a memory having a sequence of instructions which control the operation of processing unit  38  stored therein. As a variation, processing unit  38  may be formed by a dedicated electronic circuit. Processing unit  38  is capable of providing a set point value C to control unit  40  of electric motor  42 , particularly according to signal S. As an example, set point value C is all the higher as the action exerted by the driver on brake pedal  27  is significant. 
         [0044]    Control unit  40  for example comprises a circuit capable of controlling the torque and/or the rotation speed of electric motor  42  according to set point value C, for example, by adapting the power supply current and/or voltage of motor  42 . 
         [0045]    Electric motor  42  may be powered with an electric power source, for example, obtained from the voltage delivered by the vehicle battery. Electric motor  42  for example is a rotating motor, particularly a DC current rotating motor. Electric motor  42  is capable of exerting, via drive mechanism  44 , a traction on cable  46  for pulling brake  18  having an intensity depending on set point value C. 
         [0046]    Drive mechanism  44  is located between electric motor  42  and cable  46 . It has the function of transforming the rotating motion of electric motor  42  into a motion of translation of cable  46 . It may be a rack drive mechanism or a screw/nut type drive mechanism. Preferably, it is a reversible drive mechanism to enable cable  46  to return to its released position when electric motor  42  is not powered. Cable  46  is connected at one end to a lever located in brake  18 , as described in further detail hereafter, and is connected, at the opposite end, to drive mechanism  44 . 
         [0047]    Assistance device  32  is capable of controlling a braking action of brake  18  simultaneously to the braking action controlled by master cylinder  20 . 
         [0048]    According to an embodiment, assistance device  32  further comprises a force sensor, not shown in  FIG. 2 , capable of providing processing unit  38  with a signal representative of the intensity of the fraction exerted on cable  46 . Processing unit  38  then implements a feedback loop to adapt the value of set point value C according to the intensity of the traction really exerted on the cable. 
         [0049]      FIG. 3  shows an embodiment of a disk brake  50  capable of corresponding to brake  18  of  FIG. 2 . Brake  50  comprises at least one disk  52  rotated by the vehicle wheel, not shown, and located between two friction pads  54 ,  56 . Brake  50  comprises a cylinder  58  connected to friction pad  54  by a caliper  60 . A piston  62  is assembled to freely slide in cylinder  58 . Piston  62  defines with cylinder  58  a chamber  64  filled with the brake fluid and which communicates with pipe  24 , not shown in  FIG. 3 , through an opening  66 . Brake  50  further comprises a axis  68  slidably assembled on cylinder  58  and capable of being displaced in translation with respect to cylinder  58  via a tappet  70  actuated by a lever  72 . Lever  72  may be pivoted via cable  46 . The end of axis  68  comprises a threaded portion  74 . A nut  76  is arranged on threaded portion  74 . A torsion spring  78  bears against piston  62  at one end and against nut  76  at the opposite end. Brake  50  further comprises a washer  80 , fixed with respect to piston  62 , and a ball thrust bearing  82 , between nut  76  and washer  80 . Resilient return means  84 , for example, comprising Belleville spring washers, connects one end of axis  68  to cylinder  58 . The system comprising nut  76 , spring  78 , washer  80 , and bearing  82  is a system for compensating for the pad wearing. 
         [0050]    The hydraulic control of brake  50  operates as follows. Under the action of the pressure of the brake fluid penetrating in chamber  64 , piston  62  displaces in cylinder  58  and pushes pad  56  against disk  52 . By reaction, caliper  60  displaces in turn to come into contact with second pad  54  on the other surface of disk  52 . During the stroke of piston  62 , washer  80  may stop against ball thrust bearing  82 . If the stroke of piston  62  is significant, nut  76  may be driven by ball thrust bearing  82  and washer  80 . The displacement of nut  76  causes a rotation thereof around threaded portion  74  which has its rotation stopped by tappet  70  and lever  72 . The rotation of nut  76  is eased by spring  78  fastened to piston  62  and stressed in its spiral unwinding direction. At the brake release, spring  78  is stressed in its spiral winding direction and blocks the rotation of nut  76 . 
         [0051]    The mechanical control of brake  50  operates as follows. A traction on cable  46  causes a pivoting of lever  72 . Under the action of lever  72  and of tappet  70 , axis  68  displaces with respect to cylinder  58  until nut  76  comes into contact with piston  62 . Axis  68  then causes the sliding of piston  62  inside of cylinder  58 . This puts pad  56  into contact with disk  52 . When the traction on cable  46  stops, lever  72  resumes its initial position under the return effort of washers  84 . Screw/nut system  74 ,  76  enables to take into account the wearing of pads  54 ,  56 . Indeed, according to the wearing of the system, spring  78  more or less strongly unscrews nut  76 , which enables to increase the stroke length to catch up on the pad wearing. 
         [0052]      FIG. 4  shows an embodiment of a drum brake  90  capable of corresponding to brake  18  of  FIG. 2 . Brake  90  is mounted on a support, not shown, fixed with respect to the vehicle frame. Brake  90  comprises two brake shoes  92 ,  94 , each brake shoe  92 ,  94  being provided with a friction lining  96 ,  98 . Brake  90  comprises a slave cylinder  100 , attached to the support and connected to an upper end of each brake shoe  92 ,  94 . Cylinder  100  is further connected to the hydraulic circuit of the braking system. The lower ends of brake shoes  92 ,  94  may stop against a guide  102  attached to the support. Brake shoes  92 ,  94  are connected to the support via anchor springs  104 ,  106  allowing a displacement of limited amplitude of brake shoes  92 ,  94  with respect to the support. The upper ends of brake shoes  92 ,  94  are connected to each other by a spring  108  and the lower ends of brake shoes  92 ,  94  are connected to each other by a spring  110 . 
         [0053]    Brake  90  further comprises a lever  112  on which cable  46  is capable of exerting a force along arrow  114 . Lever  112  is pivotally assembled with respect to brake shoe  92  at the level of a pin joint  116 . Lever  112  is connected to an additional lever  118  via an adjustment mechanism  120  which enables to compensate for the wearing of friction linings  96 ,  98 . Additional level  118  is assembly to freely rotate with respect to brake shoe  94  around a pin joint  122 . Additional lever  118  is connected to brake shoe  92  by a connecting rod  124 . 
         [0054]    The hydraulic control of brake  90  operates as follows. When a brake fluid overpressure penetrates into cylinder  100 , this causes a displacement of the pistons of cylinder  100 , which spaces apart the upper ends of brake shoes  92 ,  94 . Friction linings  96 ,  98  come into contact with the drum, not shown, of the vehicle wheel to perform the braking operation. When the brake fluid pressure drops, the shoes are taken back to their position of rest by return springs  108 ,  110 . 
         [0055]    The mechanical control of brake  90  operates as follows. A traction on cable  46  causes a pivoting of braking lever  112  around pin joint  116 . This causes, via adjustment mechanism  120 , a pivoting of secondary lever  118  and a displacement of connecting rod  114 , whereby brake shoes  92 ,  94  are spaced apart until friction linings  96 ,  98  come into contact with the wheel drum. When the traction on cable  46  stops, the shoes are taken back to their position of rest by return springs  108 ,  110 . 
         [0056]      FIG. 5  shows an embodiment of a braking system  130  where the assistance device comprises a single electric motor for all four brakes  12 ,  14 ,  16 , and  18  of the vehicle. In this case, in addition to being connected to brake  18  by cable  46 , drive mechanism  44  is connected to brake  12  by a cable  132 , to brake  14  by a cable  134 , and to brake  16  by a cable  136 . 
         [0057]      FIG. 6  shows an embodiment of a braking system  140  where, as compared with braking system  130  shown in  FIG. 5 , drive mechanism  44  is only connected to rear left brake  16  and to rear right brake  18 . The assistance device further comprises a control unit  142  connected to processing unit  38 , a motor  144  controlled by control unit  142 , and a drive mechanism  146  connected to motor  144 . Control unit  142 , motor  144 , and drive mechanism  146  are similar, respectively, to control unit  40 , to motor  42 , and to drive mechanism  44 . Drive mechanism  146  is for example connected to front left brake  12  by a cable  148  and to front right brake  14  by a cable  149 . 
         [0058]      FIG. 7  shows another embodiment of a braking system  150  where, as compared with braking system  140  shown in  FIG. 6 , drive mechanism  44  is only connected to rear right brake  18 . The brake-assist device further comprises a control unit  152  connected to processing unit  38 , a motor  154  controlled by control unit  152 , and a drive mechanism  156  connected to motor  154 . Control unit  152 , motor  154 , and drive mechanism  156  are similar, respectively, to control unit  40 , to motor  42 , and to drive mechanism  44 . As an example, drive mechanism  156  is only connected to rear left brake  16  by a cable  158 . 
         [0059]      FIG. 8  shows another embodiment of a braking system  160  where, as compared with braking system  150  shown in  FIG. 7 , drive mechanism  146  is only connected to front right brake  14 . The assistance device further comprises a control unit  162  connected to processing unit  38 , a motor  164  controlled by control unit  162 , and a drive mechanism  166  connected to motor  164 . Control unit  162 , motor  164 , and drive mechanism  166  are similar, respectively, to control unit  40 , to motor  42 , and to drive mechanism  44 . As an example, drive mechanism  166  is only connected to front left brake  12  by a cable  168 . 
         [0060]    The previously-described embodiments of braking systems  30 ,  130 ,  140 ,  150 ,  160  enable to carry out a brake-assist function. Advantageously, they may be implemented with conventional brakes comprising a hydraulic control, conventionally used for braking operations when the vehicle is moving, and a mechanical control, for example, by cable, conventionally used to carry out a parking brake function. However, according to the present embodiments of the braking system, the mechanical control is further used to carry out the brake-assist function when the vehicle is moving, that is, jointly with the hydraulic control. 
         [0061]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further be used to carry out a parking brake function. The mechanical control of the brakes may be actuated by a button, for example placed on the central console behind the gear lever. This advantageously enables to free the location usually provided for the hand brake lever. The parking brake function is obtained by actuating the electric motor or the electric motors on the brakes of the rear and/or front axles. As an example, as soon as the driver presses on the parking brake button, the electric motor or the electric motors exert a traction on the cables, which actuates the brakes. 
         [0062]    According to an embodiment, the vehicle may further comprise an inclination sensor which is used to detect the pavement inclination. To achieve the parking brake function, the traction force to be exerted on the cables can then be determined by processing unit  38  according to this inclination. As an example, the pulling is all the stronger as the inclination is strong. To achieve the parking brake function, the brake-assist device further comprises locks capable of preventing the return to the released position of the cables when the electric motor(s) are not longer supplied with current. The lock can then be unlocked when the driver deactivates the parking brake. 
         [0063]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further be used to carry out a hill start assistance function. Such a function enables to avoid for the car to move backwards or to stall during a hill starting. To carry out this function, the vehicle further comprises one sensor or more, capable of indicating to processing unit  38  that the driver intends to start. As an example, the vehicle comprises a sensor housed on the clutch pedal, capable of providing processing unit  38  with a signal representative of the fact that the driver presses on the clutch pedal and/or another sensor housed in the gear box, capable of providing processing unit  38  with a signal representative of the fact that the driver sets a speed ratio. Further, processing unit  38  may receive a signal representative of the drive torque applied to the wheels. According to all these data, processing unit  38  may control the application of a force adapted to the brake control cables. 
         [0064]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further be used to carry out a motor brake function. As an example, the motor brake function by the braking system may be achieved when the vehicle battery is fully charged so that the driver has the same driving sensation independently from the battery state of charge. Indeed, when the battery is being charged, the driver feels a braking which is due to the portion of the energy supplied by the vehicle wheel drive motor, used to drive the alternator recharging the battery while this braking is absent when the battery is fully charged. 
         [0065]    For this purpose, processing unit  38  may adapt the application force of brakes  12 ,  14 ,  16 ,  18  according to the braking force due to the battery charge. When the driver lifts his/her foot off the accelerator pedal and the battery is fully charged, the brake-assist device may provide a braking force to replace the braking force which would be present if the battery was charging. In the embodiments previously described in  FIGS. 6 ,  7 , and  8 , the braking effort may be provided on the front wheels only. This advantageously enables the driver to have exactly the same driving sensation, for a front-wheel drive vehicle, as when the motor brake is present. 
         [0066]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further play the role of an anti-lock braking system ABS. Processing unit  38  is then capable of controlling the decrease, or even the stopping, of the braking action exerted by the brake on the corresponding wheel in the case where this wheel is about to be totally blocked by the brake. 
         [0067]    On a conventional hydraulic braking system such as shown in  FIG. 1 , the anti-lock function is obtained by additional hydraulic groups enabling to regulate the pressure in the slave cylinders of the brakes so that the wheels remain within a sliding range generally between 10% and 30%. 
         [0068]    In the embodiment shown in  FIG. 8  where the brake-assist device may perform an independent braking for each wheel, the vehicle may comprise a rotation speed sensor for each wheel providing processing unit  38  with a signal representative of the wheel rotation speed. Processing unit  38  is capable, based on the information from the speed sensor, of independently controlling each electric motor  42 ,  144 ,  154 ,  164  to decrease the brake-assist force if the associated wheel is about to be locked. In the embodiments shown in  FIGS. 5 ,  6 , and  7  where a braking action is performed simultaneously at least on two wheels, an anti-lock function for these wheels may be generally provided on the wheels, even if only one of them tends to lock. 
         [0069]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further enable to carry out a braking correction function. Indeed, during a braking, a phenomenon of mass transfer from the back to the front of the vehicle occurs. This may cause a locking of the back wheels if the braking action on these wheels is too strong. On a conventional hydraulic braking system such as that shown in  FIG. 1 , hydraulic corrector  26  is provided to decrease the brake fluid pressure transmitted to the rear brakes. In the embodiments previously described in  FIGS. 5 to 8 , the hydraulic corrector is not present. For the embodiment previously described in  FIG. 5 , the difference between the braking intensities of the rear brakes and of the front brakes may be obtained by a mechanism of adaptation to the level of drive mechanism  44  of by different lever structures at the level of rear brakes  16 ,  18  with respect to front brakes  12 ,  14 . For the embodiments previously described in  FIGS. 6 to 8 , the difference between the braking intensities of the rear brakes and of the front brakes may be calculated by processing unit  38 , which independently controls the electric motor or the electric motors associated with the front wheels and the electric motor or the electric motors associated with the back wheels. Further, the brake-assist difference between the rear brakes and the front brakes may be adapted according to the vehicle load. 
         [0070]    Braking system  30 ,  130 ,  140 ,  150 ,  160  may further enable to carry out an emergency brake-assist function. The vehicle then further comprises a sensor, for example, a speed or acceleration sensor, at the level of brake pedal  27 , capable of providing processing unit  38  with a signal representative of the rapidity with which the driver presses on the brake pedal. Processing unit  38  can then detect an emergency situation when the speed at which the driver presses on brake pedal  27  exceeds a threshold. Processing unit  38  can then control the obtaining of a maximum braking effort as rapidly as possible. 
         [0071]    As a variation, a booster battery in addition to the main battery of the vehicle may be provided to guarantee the use of the brake-assist device in case of an electric power loss of the vehicle. 
         [0072]    Specific embodiments have been described. Various alterations and modifications will occur to those skilled in the art. In particular, although the previously-described embodiments describe the use of a brake pedal, it should be clear that the present embodiments can be implemented with any type of braking actuation member, for example, a manual control at the steering wheel. Further, although the use of rotating electric motors has been described in the previously-described embodiments, it should be clear that the present embodiments can be implemented with electric stepping motors.