Abstract:
A vehicle braking assembly comprising a master cylinder ( 10 ) with no central valves, a brake fluid reservoir ( 62 ) mounted separately from the master cylinder ( 10 ), pumps ( 50 ) for pressurizing the brake fluid and first solenoid valves ( 68 ) in pipes ( 66 ) connecting the brake fluid reservoir ( 62 ) to the inlets of the pumps ( 50 ). According to the invention, a calibrated orifice ( 76 ) and a nonreturn valve ( 78 ) which are connected in parallel are mounted in these pipes ( 66 ).

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
       [0001]    This invention concerns a braking installation for a motor vehicle, said installation comprising a master cylinder controlled by a brake pedal and connected to feed circuits for the wheel brakes, as well as a hydraulic unit comprising brake fluid pressure pumps, these pumps being connected to the wheel-brake feed circuits and controlled by a computer. 
         [0002]    In such an installation, braking is controlled primarily by the driver of the vehicle using the brake pedal which is connected to the pistons of the master cylinder by a pneumatic brake booster, the action of the driver on the brake pedal causing the vehicle to brake. 
         [0003]    The operation of the brake fluid pressure pumps is controlled by the wheel traction control, wheel antilock and drive stability control computer, the computer controlling both the pumps and solenoid valves assembled in the wheel-brake feed circuits, in order to act selectively on one and/or the other of the wheel brakes of the vehicle. 
         [0004]    Furthermore, the document FR 2 645 816 makes reference to a braking system comprising a master cylinder and remote brake fluid reservoir. 
         [0005]    In these installations, a brake fluid reservoir is conventionally attached to the master cylinder and communicates with each of its chambers via brake-fluid feed and return conduits, the pistons of the master cylinder being fitted with conduits and brake-fluid valves. This known arrangement has the drawback of permitting travel and increasing the number of components in the master cylinder. 
         [0006]    This invention is particularly intended to resolve these drawbacks in the prior art. 
         [0007]    It concerns an installation of the type detailed above, whose master cylinder has a structure that is more simple than in the prior art and comprises fewer components and in which the travel is eliminated or at least reduced. 
         [0008]    Accordingly, it provides a braking installation for a motor vehicle, comprising a brake fluid reservoir, a master cylinder controlled by a brake pedal and connected to feed circuits for wheel brakes, and a hydraulic unit comprising brake fluid pressure pumps, connected to the wheel-brake feed circuits and controlled by a computer, said installation being characterized in that the brake fluid reservoir is linked to said pumps by the first solenoid valves controlled by the computer and that it is separate from the master cylinder. 
         [0009]    Thanks to the invention, it is no longer necessary to provide conduits or valves for brake fluid in the pistons of the master cylinder whose structure is considerably simplified. 
         [0010]    This makes it possible to reduce or eliminate travel in the master cylinder and to install the reservoir remotely on the master cylinder, advantageously on the aforementioned hydraulic unit. 
         [0011]    The reservoir is linked to the pumps of the hydraulic group directly without passing via the master cylinder, which makes it possible to increase the flow rate of the brake fluid supplying the pumps, to reduce the pressurization time in the wheel-brake feed circuits, and also to reduce the spurious noise related to the transfer of brake fluid to the pumps in the hydraulic unit. 
         [0012]    According to another feature of the invention, the second solenoid valves controlled by the computer are assembled in the wheel-brake feed circuits between the master-cylinder outputs and the pump outputs. 
         [0013]    This feature makes it possible to isolate the master cylinder of the hydraulic unit during operation of the hydraulic-unit pumps, such that the pressurization of the brake fluid in the wheel-brake feed circuits caused by operation of the pumps, does not affect the master cylinder, thanks to the closure of the second solenoid valves, and consequently it is not felt in the pedal. 
         [0014]    These second solenoid valves are open in idle position to enable application of the brakes from the master cylinder and are closed by the computer, when the hydraulic unit is working. 
         [0015]    Non-return valves are fitted in parallel on the second solenoid valves to prevent the backflow of brake fluid from the wheel brakes to the master cylinder. 
         [0016]    In a first embodiment of the invention, the aforementioned first solenoid valves connect the reservoir to the inlets of the hydraulic-unit pumps. 
         [0017]    Potentially, a calibrated orifice and a non-return valve, connected to each other in parallel are assembled in the conduits linking the reservoir to the pump inlets. 
         [0018]    In an alternative embodiment of the invention, the first solenoid valves link the reservoir to the pump outputs whose inlets are linked to the reservoir via conduits comprising non-return valves preventing the passage of brake fluid towards the reservoir. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]    The invention will be better understood and further features, details and advantages thereof will become clearer from the description below, given by way of an example with reference to the attached drawings, in which: 
           [0020]      FIG. 1  is a schematic representation of a braking installation according to the invention; 
           [0021]      FIG. 2  is a schematic side-elevation of the master cylinder of the installation in  FIG. 1 ; 
           [0022]      FIGS. 3 and 4  are schematic views of the alternative embodiments of the braking installation according to the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0023]    The braking installation shown schematically in  FIG. 1  comprises a master cylinder  10  linked to a pneumatic brake booster  12  controlled by a brake pedal  14 , in the conventional way. 
         [0024]    The master cylinder  10  is a tandem master cylinder shown in detail in  FIG. 2 , which comprises a primary pumping chamber  16  and a secondary pumping chamber  18  delimited within the body of the master cylinder by a primary piston  20  and a secondary piston  22 , the primary piston  20  being linked by a push rod  24  to the pneumatic brake booster  12 . 
         [0025]    The return springs  26  and  28  are arranged between the primary piston  20  and secondary piston  22  and between the secondary piston  22  and the front extremity of the body of the master cylinder  10 . Each pumping chamber  12 ,  14  is linked by a conduit  30 ,  32  to the feed circuits of the brakes  34  assembled on the front wheels and rear wheels of the motor vehicle. 
         [0026]    Conventionally, the braking installation comprises two separate circuits assembled in parallel, one of which being used to supply two of the wheel brakes  34  from the output conduit  30  of the master cylinder and the other being used to supply the other two wheel brakes  34  from the other output conduit  32  of the master cylinder, these two circuits being identical. To simplify the description, only one of these circuits shall be described below. 
         [0027]    Each circuit comprises a feed conduit  36  that links an output conduit  30 ,  32  of the master cylinder to two parallel conduits  38 ,  40  each supplying a wheel brake  34 . To each feed circuit  38 ,  40  is attached a return circuit  42  fitted with a solenoid valve  44  and connected via a shared conduit  46  comprising a non-return valve  48  at the inlet of a pump  50  that is part of a hydraulic unit  52  providing wheel fraction control, wheel anti-locking and vehicle drive stability control functions. 
         [0028]    This hydraulic unit comprises the two pumps  50  mentioned above, one for each feed circuit for the wheel brakes, these two pumps being driven by a shared motor  54  controlled by a computer C. 
         [0029]    In each feed circuit, the output of the pump  50  is connected to the aforementioned feed conduit  36 , between a solenoid valve  54  assembled in the output conduit  30 ,  32  of the master cylinder and two solenoid valves  56  assembled in the conduits  38 ,  40  supplying the two wheel brakes  34  of the circuit. A non-return valve  58  is connected on a bypass around the solenoid valve  54 , in the direction that prevents the backflow of brake fluid to the master cylinder  10 , and non-return valves  60  are connected on a bypass around the solenoid valves  56  supplying the wheel brakes, in the direction that prevents the backflow of brake fluid from the wheel brakes. 
         [0030]    A brake fluid reservoir  62 , of the type comprising a filling cap  64 , is fitted to the hydraulic unit  52  and connected via conduits  66  each comprising a solenoid valve  68  at the inlets of the pumps  50  of the hydraulic unit. These solenoid valves  68 , like the solenoid valves  44  fitted in the return conduits of the brakes  34 , are of the type that are closed in idle state and opened by the computer C. 
         [0031]    The solenoid valves  54  and  56  fitted in the feed conduits of the wheel brakes  34  are of the type that are open in idle state and closed by the computer C. 
         [0032]    Finally, a brake accumulator  70  is attached to the shared return conduit  46  upstream of the non-return valve  48 . 
         [0033]    The brake fluid reservoir  62  fitted to the hydraulic unit  52  is only connected to the inlets of the pumps  50  and does not include a connection conduit to the pumping chambers  16 ,  18  of the master cylinder  10 . As shown in  FIG. 2 , the structure of this master cylinder is significantly more simple than in the prior art, on account of the absence of these connection conduits and the absence of brake fluid passages in the pistons  20  and  22  of the master cylinder and the valves fitted in these passages. 
         [0034]    The chambers  16  and  18  of the master cylinder may therefore be filled permanently with brake fluid, pressurized by the forward movement of the pistons  20 ,  22 . 
         [0035]    The bleed holes closed by the caps  72  are formed in the body of the master cylinder  10  at the front extremities of the pumping chambers  16 ,  18 . 
         [0036]    This braking installation works as follows: 
         [0037]    When the braking operation is commanded by the driver pressing on the brake pedal  14 , the brake fluid is pressurized in the output conduits  30 ,  32  of the master cylinder and in the conduits  36 ,  38 ,  40  supplying the wheel brakes  34  by moving the pistons  20 ,  22  of the master cylinder forwards, the response time of the braking circuit being very quick on account of the absence of travel in the master cylinder. 
         [0038]    The solenoid valves  54 ,  56  fitted in the feed conduits of the wheel brakes remain open until they are closed by the computer C. 
         [0039]    When the computer C detects a condition in which an action on the wheel brake  34  is required, to prevent the wheel locking or slipping or to stabilize the vehicle, it closes the solenoid valves  54  connecting the master cylinder  10  to the wheel-brake feed circuits  34 , and opens one or both of the solenoid valves  68  supplying the pumps  50  from the reservoir  62 . The computer C can therefore adjust the pressure of the brake fluid supplying each wheel brake  34  to the required value, to obtain the desired result. 
         [0040]    It may also momentarily open the solenoid valves  54  assembled in the output conduits  30 ,  32  of the master cylinder during operation of the pumps  50 , to refill the pumping chamber of the master cylinder with brake fluid, if necessary. 
         [0041]    The braking installation according to the invention that is shown in  FIG. 3  differs from that shown in  FIGS. 1 and 2  in that the brake fluid reservoir  62  does not comprise a filling cap and is sealed closed, this reservoir being connected to each solenoid valve  68  provided for at the inlet of the pump  50  of the hydraulic unit  52  by a unit comprising a calibrated orifice  76  and a non-return valve  78  arranged in parallel, the non-return valve  78  preventing the backflow of brake fluid towards the reservoir  62 . 
         [0042]    The function of this unit  76 ,  78  is to enable the unrestricted supplying of each pump  50  at the command of the computer C, the calibrated orifice  76  creating a pressure drop that prevents any excessive and dangerous overpressure in the reservoir  62  when the brake fluid returns to the reservoir, if the pressure in the wheel brakes  34  is too high. 
         [0043]    The backflow of brake fluid through the calibrated orifice  76  generates momentary residual braking torque, but guarantees the reservoir  62  against all risk of explosion. In all other respects, the braking installation in  FIG. 3  is identical to the one in  FIG. 1 . 
         [0044]    In the alternative embodiment shown schematically in  FIG. 4 , the braking installation differs from that shown in  FIG. 1  in that the brake fluid reservoir  62 , fitted to the hydraulic unit  52 , is connected to the inlet of each pump  50  by a conduit  80  fitted with a non-return valve  82  fitted in the direction preventing the backflow of brake fluid to the reservoir. A solenoid valve  84  is fitted in a conduit  86  connecting the output of the pump  50  to the reservoir  62 . As in the installation in  FIG. 1 , the output of each pump  50  is connected to the feed conduit  36  of the wheel brakes  34 , between the solenoid valve  54  assembled in the corresponding output conduit  30 ,  32  of the master cylinder and the solenoid valves  56  supplying the wheel brakes. In all other respects, the installation shown in  FIG. 4  is identical to the one in  FIG. 1 . 
         [0045]    The solenoid valves  84  fitted in the conduits  86  linking the outputs of the pumps  50  to the reservoir  62  are closed in idle state and opened by the computer C. They enable a backflow of brake fluid towards the reservoir  62 , when commanded by the computer. 
         [0046]    In the embodiments described and shown in  FIGS. 1 ,  3  and  4 , a braking command by the action of the driver on the brake pedal  14  is detected by means of a pressure sensor  88  assembled in one of the output conduits of the master cylinder  10 . In an alternative embodiment, this braking command may be detected using the output signal of a position or movement sensor that is linked to the brake pedal  14  and that controls the illumination of the stop lights, i.e. the lamps of the braking signal circuits, when the driver presses on the brake pedal  14  and takes it out of its idle position.