Abstract:
In order to address a problem with the effectiveness of a brake booster device, provision is made for the latter to be produced in the form of hydraulic servo control. In such an instance, a master cylinder ( 7 - 10 ) of a braking circuit ( 3 - 4 ) is provided with a pressure chamber ( 19 ) upstream of the braking circuit. This pressure chamber is then subjected to an injection ( 28 ) of hydraulic fluid by a pump ( 34 ). The pump is operated ( 39 ) according to the braking requirements. The servo control comprises a set of moving gear ( 54 ) sensitive to these requirements and that work an injection valve ( 29 - 30 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a hydraulic brake booster device. Such a device is more particularly intended to be installed in a vehicle, notably a vehicle of the sedan or utility type. It is an object of the invention to address problems with technological evolutions, requirements for space and manufacturing complexity. 
         [0002]    In the automotive field, brake booster devices, notably of the pneumatic or electrohydraulic type, are known. The first pneumatic booster devices in practice comprise a pneumatic servo brake, provided with a variable-volume front chamber separated from a rear chamber, which is likewise a variable-volume chamber, by a partition formed by a leaktight and flexible diaphragm and by a rigid skirt plate. The rigid plate drives a pneumatic piston which, via a push rod, bears against a primary piston of a master cylinder of a hydraulic braking circuit, typically a tandem master cylinder. The front chamber positioned on the master cylinder side is connected pneumatically to a source of fluid. The rear chamber, on the opposite side to the front chamber, is placed on the brake pedal side and is connected pneumatically, in a way controlled by a valve, to a source of driving fluid typically air at atmospheric pressure. At rest, that is to say where a driver is not depressing the brake pedal, the front and rear chambers are connected to one another while the rear chamber is isolated from atmospheric pressure. Under braking, the front chamber is first of all isolated from the rear chamber, then air is admitted into the rear chamber. This admission of air has the effect of driving the partition and of pneumatically boosting the braking. 
         [0003]    The disadvantage displayed by this type of pneumatic boosting lies in the volumetric ratio of the boost force. Specifically, because the boost force is provided by air at ambient pressure, which is not very high, the booster has to be large enough in size that the boost force will be great. When, for reasons of space, it is not possible to produce chambers with sufficiently large volumes, provision may be made for a number of chambers to be produced in a cascade configuration. Such embodiments are, however, always to the detriment of the space available in the engine compartment of the vehicle. 
         [0004]    Further, these devices by way of vacuum source for the front chamber, use a vacuum established in an engine inlet manifold. Now, with modern-day engines, the amount of air admitted is smaller, and the vacuum source becomes less effective. With diesel engine vehicles, acting in this way is not even conceivable. 
         [0005]    Also known are electrohydraulic brake booster devices. Typically, an electric motor is connected to a hydraulic pump which injects a hydraulic fluid under pressure into the braking circuits, downstream of the master cylinder, at the time that these circuits are called into action. Control over this electric motor is achieved via measurements of the pressures obtaining in the front and rear chambers of the pneumatic servo brake. Such a solution presents numerous disadvantages. 
         [0006]    First, the boost pumps used have therefore to be high-pressure pumps, capable of a constant delivery. In practice, they have to be driven by high-powered motors, typically having a power of 1 kilowatt. Even for a vehicle with a powerful combustion engine, developing 100 kilowatts for example, this brake boosting alone represents 1% of the power developed by the engine, and this is too much. 
         [0007]    Technologically, the pumps supply a high pressure. An orifice plate interposed in a return circuit leading to the reservoir, controlled on the basis of the pressure measurements, allows a hydraulic liquid to be injected under variable pressure into the brake circuit. The opening and closing of the orifice plate also present problems of noise and problems associated with the difficulties associated with accurate control. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention seeks to solve these problems of space, power consumption, and difficulties of precise control by using an entirely novel design of brake boosting circuit. The brake boosting circuit of the invention can also be coupled, although this is not compulsory, to an pneumatic boosting circuit or even to an electrohydraulic boosting circuit. 
         [0009]    The principle of the invention involves adding a hydraulic servo brake or regulator which is interposed between the inlet to the master cylinder and the bearing point of the control rod transmitting the forces applied by the driver to a brake pedal. This hydraulic regulator behaves in the same way as a pneumatic servo brake. The pressure of the driver&#39;s foot on the brake pedal mechanically causes a hydraulic circuit of the master cylinder to be placed in communication with the hydraulic boost circuit driven by the pump, preferably an electric pump. 
         [0010]    The regulator for this purpose comprises an interposed intermediate cylinder with which a contiguous cylinder is juxtaposed. A set of moving gear is interposed in this contiguous cylinder and divides it into two chambers. This set of moving gear is mechanically sensitive to a difference in pressure produced in a first chamber of the contiguous cylinder, by the action of the foot on the brake pedal, and a pressure produced in a second chamber of the contiguous cylinder by the injection of the hydraulic flow from the pump. As soon as the pressure produced by the foot increases, it pushes back the set of moving gear and hydraulic fluid under high pressure is injected into the second chamber of the contiguous cylinder. 
         [0011]    A piston passes through two chambers of the intermediate cylinder. It has the special feature of having a cross section in the second chamber that is greater than its cross section in the first chamber. The action of the pump is then additionally applied in the second chamber to the difference in surface area of this piston. This piston therefore presses against a primary piston of a master cylinder, or even drives the primary and secondary pistons of a tandem master cylinder. When the driver takes his foot off the brake pedal, a valve that places the hydraulic pump in communication with the chambers of the contiguous cylinder closes, and the pressures in the regulator naturally drop because of the communication with the hydraulic reservoir. 
         [0012]    A subject of the invention is therefore a hydraulic brake booster device comprising a master cylinder provided with a primary chamber and with a primary piston incidentally moved by a control rod, characterized in that it comprises a hydraulic regulator interposed between a bearing point of the control rod and a bearing point on the primary piston. 
         [0013]    For preference, the hydraulic regulator, servo brake, comprises an interposed cylinder, interposed between a bearing point for the control rod and the primary cylinder, an extension piston bearing against the primary piston and interposed, in the interposed cylinder, between the bearing point of the control rod and the primary piston, this extension piston defining in the interposed cylinder an upstream chamber close to the control rod and a downstream chamber close to the primary piston, the extension piston having a surface of larger cross section in the downstream chamber than the one in the upstream chamber, a cylinder contiguous with the interposed cylinder, a shell, positioned in the contiguous cylinder and forming, in the contiguous cylinder, a rear chamber and a front chamber, the upstream and downstream chambers of the interposed cylinder being in communication with the rear chamber and the front chamber of the contiguous cylinder respectively, a set of moving gear positioned in the shell, a valve operated by the set of moving gear, a communication for placing a hydraulic source in communication with the front chamber via the valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be better understood from reading the description which follows and from studying the accompanying figures. These figures are given only by way of entirely nonlimiting example of the invention. The figures show: 
           [0015]      FIG. 1 : a schematic depiction of a master cylinder according to the invention; 
           [0016]      FIG. 2 : a detailed depiction of the hydraulic regulator of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is a schematic depiction of a hydraulic brake booster device  1  according to the invention. This device  1  is used in a vehicle, not depicted, to transmit a braking force applied by a driver&#39;s foot to a brake pedal  2  to a braking device  3 , typically a disk brake caliper acting on a disk  4  of a wheel of the vehicle. The device  1  may be boosted by an optional pneumatic brake booster device  5 . The force applied to the pedal  2  is thus transmitted from a control rod  6 , in this incidence the pedal  2 , to a primary piston  7 , or even preferably also to a secondary piston  8  of a tandem master cylinder. The chambers such as  9  and  10  of this master cylinder are connected by hydraulic lines such as  11  to braking devices such as  3  mounted, via independent hydraulic circuits, on the various wheels of the vehicle. 
         [0018]    According to the invention, the device  1  comprises a hydraulic regulator  12  interposed between a bearing point  13  of the control rod  6  and a bearing point at the inlet  14  to the master cylinder. The invention preferably covers an overall device, which therefore comprises the actual master cylinder proper and the regulator  12 , because for preference these two components may be formed from one and the same block of metal which has been machined from a casting. It is, however, conceivable for these two items to be manufactured separately and joined together by conventional means. 
         [0019]    The regulator servo brake  12  is thus formed of an interposed cylinder  15  which is interposed and aligned between the bearing point  13  and the bearing point  14 . Inside this interposed cylinder  15  there moves an extension piston  16 . This piston  16  slides in the cylinder  15  with the aid of a ring  17  which defines within the interposed cylinder two chambers: an upstream chamber  18  close to the control rod  6  and a downstream chamber  19  close to the primary piston  7 . One of the special features of the extension piston  16  is that it has two elements with cross-sectional surface areas  20  and  21  respectively in these chambers which are of different sizes. The cross section  21  is greater than the cross section  20 . In practice, the extension piston  16  cannot therefore pass through the ring  17  because the cross section  21  is greater than the cross section  20  which itself corresponds to the inside of the ring  17 . 
         [0020]    In addition to the interposed cylinder  15 , the regulator of the invention comprises a contiguous cylinder  22 , contiguous with the cylinder  15 . For numerous reasons, all these cylinders are preferably circular. A shuttle  23  moves inside the contiguous cylinder  22 . The shuttle  23  slides in a ring  24  bearing against the walls of the contiguous cylinder  22  so as to define therein a rear chamber  25  and a front chamber  26 . The rear chamber  25  is in communication with the upstream chamber  18  while the front chamber  26  is in communication with the downstream chamber  19 . They are in communication via communications  27  and  28  respectively. The various upstream, downstream and front, rear chambers are filled with hydraulic fluid by an ancillary device. In practice, seals mounted notably in the rings  17  and  24  prevent fluidic communications between the upstream and downstream chambers and between the front and rear chambers. 
         [0021]    The front chamber  26  comprises a valve  29 , here symbolic, depicted in the form of a check valve  30 . The valve  29 - 30  serves to place a source  31  of hydraulic pressure in communication with the front chamber  26 . The source  31  in the conventional way comprises a hydraulic fluid reservoir  32  opening via a line  33  into a constant-delivery pump  34  driven by a shaft  35  in turn driven by a motor  36 , preferably an electric motor. On the outlet side of the pump  34 , a return circuit  37  returns the hydraulic fluid, pumped from the reservoir  32 , to this same reservoir  32 . This return circuit is fitted with a controlled valve  38 . The valve  38  is controlled, in a conventional way, by a detector  39  that measures the action on the brake pedal  2  and/or the control rod  6 . 
         [0022]    The way in which this hydraulic source  31  works is known, and is as follows. When the pedal  2  is operated, the detector  39  closes the valve  38  a little. This being the case, the pump  34 , which produces a constant delivery, experiences an increase in pressure in an outlet line  40  leading to the valve  38 . This increased pressure is tapped by a tapping  41  to be applied to the valve  29 - 30  of the contiguous cylinder of the regulator  12  of the invention. The greater the extent to which the pedal is depressed, the greater the increase in pressure in the pipe  42  leading from the tapping  41  to the valve  29 - 30 . 
         [0023]    The principle of the invention is as follows. When the user depresses the pedal  2 , because of the reaction of the pistons  7  and  8  of the master cylinder, the hydraulic fluid pressure in the upstream chamber  18  increases. It therefore also increases accordingly in the rear chamber  25  because of the communication  27 . This being the case, the shuttle  23  moves and opens the valve  30 , such that the front chamber  26  of the contiguous cylinder  22  now finds itself subjected to a high pressure transmitted by the line  42 . This high pressure obtaining in the front chamber  26  is transmitted via the communication  28  to the downstream chamber  19 . 
         [0024]    The extension piston  16  is then, via the difference in surface area between the cross section  20  and the cross section  21 , subjected to a high boost pressure supplied by the pump  34 . This being the case, the extension piston  16 , which bears  14  against the primary piston  7  of the master cylinder, applies to the latter a greater, boosted, force, causing better braking of the brake disk  4 . 
         [0025]      FIG. 2  reconsiders the same elements in detail and leads to a practical embodiment of the schematic device shown in  FIG. 1 . It shows various other features of the device of the invention. First, the master cylinder comprising a regulator can be produced either in a single operation or produced using two components: a doubly cylindrical first component  43  that forms the actual regulator proper, as shown in  FIG. 2 , and a conventional component  44  that forms the master cylinder. The component  43  comprises a block pierced with the interposed cylinder  15  and with the contiguous cylinder  22 . Hydraulic fluid is distributed both to the master cylinder  44  and to the regulator  43  by a bore  45  aligned with each of these two components and leading to the reservoir  32 . Where they are joined together, the two components  43  and  44  are fitted with seals such as  46 , to prevent leaks. The bore  45 , in its portion that enters the component  43 , terminates at one end in a communication  48  via which the hydraulic fluid can enter the intermediate cylinder  15 . 
         [0026]    The intermediate cylinder  15  has, between the location of the ring  17  and the inlet via which the control rod  6  enters, a bore with a cross section  49  which is somewhere between the cross section  20  and the cross section  21 . For example, in this bore  49 , near the point of introduction of the rod  6 , a set of O-ring seals such as  50  and  51  allow the upstream chamber  18  to be filled with hydraulic fluid, without external leakage, when the rod  6  is in the retreated position. Furthermore, these seals allow the pressure in the upstream chamber  18  to rise when this rod  6  is depressed, by preventing fluid from returning back to the reservoir  32 . 
         [0027]    For this purpose, the control rod  6  is equipped at its end introduced into the interposed cylinder  15  with a bell housing  52  provided with peripheral openings  53  which, when the control rod  6  is in the rest position, lie facing the opening  48 . In this rest position, the seal  50  prevents the hydraulic fluid from traveling back along the rod  6 . As soon as the control rod  6  is depressed and the location of the openings  53  moves beyond the seal  51 , the latter prevents the hydraulic fluid trapped in the chamber  18  from traveling back toward the reservoir  32 . This being the case, the pressure in the chamber  18  increases. 
         [0028]    This increase has two effects: first, the extension piston  16  receiving this pressure on its cross section  20  is driven and via its end  7  which acts as the primary piston of the master cylinder, applies the pressure necessary for braking. Second, because the pressure in the chamber  18  has increased, it causes fluid to pass into the communication  27  between this upstream chamber  18  and the rear chamber  25  of the contiguous cylinder  22 . The shuttle  23  itself has two special features: firstly it is deformable and secondly it drives a set of hollow moving gear  54 . The shuttle  23  is thus made up of a mount  55  able to move globally past the communication  27  and of a fixed shell  56 , globally facing the communication  28 . 
         [0029]    The mount  55  rests against a closed end of the rear chamber  25  via a pedestal  57 , while the shell  56  rests against the roof of the front chamber  26  via a stop  58 . A coil spring  59  keeps the mount  55  and the shell  56  apart. The mount  55  can run in the chamber  25 , moving closer to the shell  56 . The mount  55  also bears against a ball  60  which, by reaction, presses against a coil spring  61  contained in the set of moving gear  54 . The set of moving gear  54  is provided at an opposite end to the one that accepts the ball with a post  62  intended to press against a ball that forms the shutter  30  of the valve  29 . The ball  30  is held against the seat of the valve  29  by a spring  63  which bears against a structure of the shell  56 . 
         [0030]      FIG. 2  shows the start of a demand for boosted braking. For example, the rod  6  has already been inserted slightly into the interposed cylinder  15  and the openings  53  are just about to move beyond the O-ring seal  51 . When they have moved beyond it, the upstream chamber  18  will be closed off. When it is closed off, continued pressure on the control rod  6  will cause the mount  55  resting against the closed end of the rear chamber  25  to move away therefrom because of the increase in pressure in the chambers  18  and  25 . The mount  55  will then press against the ball  60 . Initially, the ball  60  will push back the spring  61  with no further effect. After a certain travel has been covered, which is as short as possible in order to avoid excessive dead travel of the pedal  2 , the ball  60  will come to bear cleanly against an edge  64  of the set of moving gear  54 . 
         [0031]    Because of this clean bearing, firstly, the set of hollow moving gear  54  is closed off. Secondly, the advancing travel of the mount  55  causes the set of moving gear  54 , and notably its post  62 , to move toward the ball  30 . The set of moving gear itself is normally pushed back toward the mount  55  by a spring  64  bearing against a body of the shell  56 . The shell  56  is a hollow piston provided with a fixed dividing partition  65 . This fixed partition  65  acts as a seat for the valve  29 . This fixed partition  65  divides the hollow shell  56  into two parts: a first part that forms the front chamber  26  and a second part that forms an access chamber  66  in communication, via communications such as  67 , with the line  42 . 
         [0032]    When the post  62  presses against the ball  30 , this ball allows the pressure produced by the pump  34  ( FIG. 1 ) to enter and progress as far as the chamber  26 . The chamber  26  is formed firstly by the hollow part of the shell  56  and secondly by an annular space with which it communicates via holes such as  68  in the wall of the shell  56 . This annular space is itself in communication with the downstream chamber  19  via the communication  28 . 
         [0033]    The advancing travel of the rod  6  has therefore caused the mount  55  to advance, has caused the set of moving gear  54  to advance, has opened the valve  29  and has placed the chamber  19  under pressure using the pressure of the liquid supplied by the line  42 . This being the case, the extension piston  16  finds itself subjected, via a peripheral annulus  69 , to the additional pressure applied by the pump  34 . This additional pressure causes the piston  16  to move toward the master cylinder, to the left in  FIG. 2 . 
         [0034]    This being the case, for a given position of the control rod  6  (supposed to be kept fixed in a braking position), the upstream chamber  18  sees its volume increase because the extension piston  16  escapes toward the master cylinder under the effect of the hydraulic boost. This being the case, the pressure in this upstream chamber  18  drops, leading to the drop in pressure in the rear chamber  25 . As the pressure in the chamber  25  drops, the mount  55  retreats as, ultimately do the ball  60  and the set of moving gear  54 . This being the case, the valve  29  closes by the ball  30  returning to bear against its seat  65 . By acting in this way, servo control of position has been achieved. If the rod  6  is moved forward again a little, the same phenomenon recurs, the shell compresses and the mount  55  moves forward until the advancing travel of the extension piston  16  is enough to return them to equilibrium. 
         [0035]    Upon brake release, control of the valve  38  leads to a drop in pressure in the line  42 . At the same time, the situation is one in which the pressure in the downstream chamber  26  is higher than the pressure present in the access chamber  66 . In order to discharge this additional pressure, the set of moving gear  54 , of hollow tubular shape and containing the spring  61  at its center, is provided with a set of peripheral holes such as  70 . For example, four peripheral holes lead from the chamber  26  into the bore of the set of moving gear  54 . The high pressure available in the chamber  26  can thus escape as far as the chamber  25  where it contributes to allowing the mount  55  to return against the end wall of the chamber  25  because also the ball  60  is no longer blocking off the hollow part of the set of moving gear  54 . The intermediate chamber between the mount  55  and the shell  56  is also placed in communication, by means which have not been depicted, with the reservoir  31  via a line of the same type as the bore  45 . At rest, the pressure between the mount  55  and the shell  56  is therefore equalized with the pressure in the chambers  25  and  26 . 
         [0036]    From an industrial standpoint, the interposed cylinder  15  is mounted in the precise continuation of the cylinder of the master cylinder. In this way, the extension piston can quite simply be formed of an extension screwed into a support  14  of the master cylinder piston. 
         [0037]    In order to mount the set of moving gear  54  and the shell  56  in the contiguous cylinder  22 , the procedure followed is this: first, the ball  30  is placed on the seat  65  and the spring  63  is mounted on top of the ball  30  and held there by a cover. Next, the spring  64  is fitted into the chamber  26 . The seat and cover assembly is then mounted in the closed end of the shell  56  where it is held in position by a screw-on cap  71 . This cap  71  comprises the stops  58 . Next, the set of moving gear  54  is slipped into the ring  24  formed in the shell  56 . Next, the spring  61  is mounted in the bore of the set of moving gear  54  before the ball  60  is placed on top. When the ball  60  is in place, a retaining ring  72 , surmounted by a washer  73 , is screwed from the other side of the shell  56  to prevent the set of moving gear  54  from escaping. This set of moving gear nonetheless maintains its mobility, notably under the effect of the spring  64 . Next, the spring  59  is fitted around the ring  72  and the washer  73 . Next, the mount  55  is slipped into position with its end intended to press against the ball  60  in the spring  59 . That assembly is then mounted inside the contiguous cylinder  22  which is plugged by a screw-on end piece  74 . The assembly thus produced is then ready for use. For its part, an element of the extension piston  16  is screwed onto another element that forms the primary piston  7  before being fitted into the ring  17 , present in the interposed cylinder  15 . 
         [0038]    The relationship between the input force Fe bearing against the rod  6  and the pressure Pp in the primary chamber of the master cylinder is Fe=Pp×(S4×S3×S6/(S2×(S6−S5)+S4×S5)). 
         [0039]    The modulated pressure Pm available in the chamber  26  is then equal to Pm=Pp×((S2×S6/(S2×(S6−S5)+S4×S5)), neglecting the forces of the various springs. In one example, the diameters of the various circular cross sections S2 to S6 are 27.6 mm, 20.6 mm, 10 mm, 15 mm and 23.8 mm, respectively. These dimensions, with an applied force of 53 daN, and with a maximum pressure delivered by the pump of 123 000 HPa, lead to an additional pressure in the boost chamber of 80 000 HPa, namely a considerable boost force of around 560 daN. 
         [0040]    Choosing a DC motor  36  with which to drive the pump  34 , in which motor the torque available is proportional to the current, is a preferred solution because the transfer function is simple. Further, a DC motor, also known as a torque motor, has the advantage of being very well able to withstand blocking. For example, the pump may then be of the lifting and forcing type (without reverse leakage). Nonetheless, it could also be of the peristaltic, diaphragm or vane type or, more generally, of a positive-displacement type. The last three types do not cause the motor to stop when the pressure in the chamber  6  reaches the desired value. With the device of the invention, it even becomes possible to stop the pump. Specifically, once braking is over, there is no longer any need to continue to run the motor  36 , hence saving energy.