Abstract:
The invention relates to a hydraulic vehicle brake system having a service brake which can be actuated by muscle force and having a device for regulating the wheel slip. It is proposed in such a vehicle brake system to use suction pumps in connection with specially-designed accumulators. The accumulators have separating elements which in each case separate a first accumulator chamber from a second accumulator chamber. An inflow opens out into the first accumulator chamber, and an outflow, which is separate from the inflow, outlets out of the first accumulator chamber. The separating element is arranged so as to be freely movable between two end positions, and in one of its end positions, blocks a pressure medium connection of the inflow to the outflow.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/054051 filed on Apr. 25, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a hydraulic vehicle brake system having a service brake that can be actuated by muscle force and having a device for regulating wheel slip. 
     2. Description of the Prior Art 
     Wheel-slip-regulated vehicle brake systems are understood hereinafter to mean anti-lock vehicle brake systems (ABS), vehicle brake systems with traction control (TC), or vehicle brake systems with an electronic stability program (ESP). Such vehicle brake systems have a hydraulic unit connected between a master cylinder, which is actuatable by the driver, and at least one wheel brake. This hydraulic unit is equipped with, among other elements, magnetically actuatable multi-way valves, pumps, a pump drive, and reservoirs that supply the pumps with pressure fluid. For actuating the pump drive, a drive motor is also present. Via an electronic control unit, the drive motor and the multi-way valves can be triggered for regulating the pressure in the wheel brakes as needed. Detailed information going beyond this can be found in the discussion in the brochure entitled “ Fachwissen Kfz-Technik, Sicherheits - und Komfortsysteme, Fahrstabilisierungssysteme ” [Automotive Technology, Safety and Comfort Systems and Stabilizing Systems],  Gelbe Reihe  [Yellow Series], 2004 Edition, Robert Bosch GmbH, Stuttgart, ISBN 3-7782-2026-8, in particular beginning on page 90. 
     The vehicle brake systems described therein are similar to one another in terms of the layout of their hydraulic circuit diagram, but they differ in their engineering effort and expense depending on the scope of their function. In practice, for instance, different structural forms of pumps and/or a greater or lesser number of differently designed multi-way valves are used in order to achieve whatever functionality is wanted. Anti-lock vehicle brake systems, for instance, make do with non-self-aspirating pumps, known as return pumps. The object of these pumps, in a braking event involving existing wheel slip, is to pump pressure fluid from an affected wheel brake back to the master cylinder in order to lower the brake pressure. Since because of the actuation of the master cylinder by the driver taking place at that time the pressure fluid in the wheel brake is already at elevated pressure, the pump itself need not perform any suction work. 
     Vehicle brake systems with a TC or ESP function, by comparison, must be capable of building up a brake pressure in one or more wheel brakes, regardless of any actuation of the master cylinder by the driver, so as to eliminate the wheel slip occurring upon acceleration of the vehicle or on cornering. This requires pumps that are designed to be self-aspirating. Self-aspirating pumps are capable of pumping pressure fluid even if there is no pressure difference or only a slight pressure difference at their inlet side. An exemplary embodiment of a self-aspirating pump is already known for instance from German Patent Application DE 199 28 913 A1. 
     Regardless of the type of vehicle brake system, the pumps are preceded by hydraulic reservoirs. These reservoirs make pressure fluid available to the pumps and thereby assure pump startup. Known vehicle brake systems use spring piston reservoirs for this purpose. These reservoirs include a piston, guided movably in a reservoir housing, which by circumferential sealing divides a first storage chamber, which can be filled with pressure fluid, from a second storage chamber, which is filled with a gas. The piston is urged by a spring in the direction of its basic position. In this basic position, there is no pressure fluid in the first storage chamber. In known reservoirs, the inflow and outflow of pressure fluid take place through a common supply conduit. Such reservoirs are described for instance in German Patent Application DE 199 42 293 A1. 
     In the event of an emptied reservoir, to prevent pressure fluid aspirated from the master cylinder by the pump from flowing to the storage chamber, a check valve is disposed in the supply line to such a reservoir. Known check valves have a valve closing body, acted upon by a spring, for controlling a valve seat. 
     A defective, leaky check valve, in conjunction with the sole supply conduit of the reservoir, would have the effect that the underpressure generated by the self-aspirating pump could affect the wheel brakes. Because of this underpressure, the brake pistons of these wheel brakes will be put in an extreme position. In a subsequent braking event, a disproportionately large amount of pressure fluid would therefore have to be positively displaced into the wheel brakes for the sake of building up brake pressure. The driver could perceive this from a long pedal travel, which could be irritating with regard to the capability of the vehicle brake system to function. 
     Furthermore, the number of different components for vehicle brake systems with a variable functional scope increases the costs for development and maintenance of a modular system. In addition, relatively many individual components have to be installed to make the known vehicle brake systems, which adversely affects production costs and the resultant structural volume. Known vehicle brake systems furthermore have the potential for improvement in terms of their functional properties when brake slip regulation occurs. 
     OBJECT AND SUMMARY OF THE INVENTION 
     A hydraulic vehicle brake system according to the invention has the advantage over the prior art that it makes do with fewer different individual parts and is thus more economical. The individual parts used can be used both for anti-lock vehicle brake systems and for traction control or stability control programs. A vehicle brake system of the invention has improved functional properties during the regulation of the wheel slip, and because of the reduced number of individual parts, it makes more-compact dimensions of its hydraulic unit possible. These advantages are attained, among other ways, by the use of a self-aspirating pump for all the different kinds of vehicle brake systems, that is, including for purely anti-lock brake systems, in conjunction with hydraulic reservoirs that are each supplied with pressure fluid via an inlet and via an outlet separate from the inlet. The reservoirs used have a freely movable separator element, disposed between two end positions, for dividing a first storage chamber from a second storage chamber. Furthermore, this separator element is capable, in one of its end positions, of blocking off a pressure fluid-conducting connection from the inlet to the outlet of the reservoir. It functions without an additional spring element, and as a result, the volume of pressure fluid that can be stored in the storage chamber is increased, in comparison to a spring piston reservoir, while the dimensions are unchanged. Moreover, the reservoir has a pressure/volume characteristic curve with improved hysteresis, since the influence of the spring element on the hysteresis is eliminated. Further advantages or advantageous refinements of the invention will become apparent from the ensuing description. 
     A check valve of special embodiment is disposed in the outlet of the reservoir. This check valve prevents a return flow of pressure fluid to the storage chamber of the reservoir and, because of the additional sealing function of the separator element of the reservoir, it can also be embodied without a restoring spring. Besides the savings in terms of parts costs, the check valve thus is more compact and more economical, compared to known arrangements. Such a check valve is necessary only in vehicle brake systems with an electronic stability program or traction control, since in those cases a buildup of brake pressure can occur independently of the driver, and since for this pressure buildup, pressure fluid may under some circumstances have to be aspirated from the master cylinder by the pump. In that case, the check valve prevents pressure fluid coming from the master cylinder from flowing into the reservoir. Anti-lock vehicle brake systems make do without this check valve. 
     Alternative variant embodiments for a reservoir according to the invention, with a separator element that seals off in one end position are equally advantageous with respect to their small installation space and their costs. 
     An advantageous number and disposition of the inlets and outlets open into the first storage chamber of such a reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail in the ensuing description taken in conjunction with the drawings, in which: 
         FIG. 1  is a hydraulic circuit diagram showing the layout of a hydraulic vehicle brake system according to the invention. 
         FIG. 2  shows a reservoir in a first, especially preferred structural valiant embodiment, in a hydraulic block of the hydraulic brake system; 
         FIG. 3  shows second embodiment of a reservoir according to the invention; 
         FIG. 4  shows a third embodiment of a reservoir embodied as a screw-on version; 
         FIG. 5  shows a further exemplary embodiment of a reservoir, in which a hollow piston is used as a separator element; and 
         FIG. 6  shows a cross section through a reservoir, specifically in the region of the entering and leaving supply conduits. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1 , in a schematic illustration, shows the circuit diagram of a hydraulic vehicle brake system  10  having a device for regulating wheel slip. A master cylinder  14  actuatable by a brake pedal  12  can be seen, along with two interconnected wheel brakes  16  in one brake circuit. A hydraulic unit  18  is disposed between the master cylinder  14  and the wheel brakes  16 . This hydraulic unit  18  is shown in  FIG. 1  by an outline shown in dashed lines. It includes various electromagnetically triggerable multi-way valves  20 ,  22 , a pump  26  actuatable by a drive motor  24 , a hydraulic reservoir  30  supplying the pump  26  with pressure fluid, and a check valve  32  located between the reservoir  30  and the pump  26 . These hydraulic components mentioned are connected, on the basis of pressure fluid-carrying lines  34 , to form a hydraulic circuit. These lines  34  are embodied as bores in a hydraulic block  40  ( FIG. 2 ) of the hydraulic unit  18 ; in a later work operation, these bores are closed off from the outside. The aforementioned hydraulic components are also secured to the hydraulic block  40 . For their electrical triggering, an electronic control unit  42  is present, which can likewise be disposed on the hydraulic block  40 . 
     To this extent, this layout of a hydraulic vehicle brake system is prior art. For the mode of operation of this vehicle brake system, reference can therefore be made to the discussion in the brochure mentioned at the outset. 
     The invention is distinguished over the vehicle brake system explained in this brochure by the embodiment of the reservoirs  30  provided, the connection of these reservoirs  30  to the hydraulic circuits, and the structural embodiment of the check valves  32  employed. The modified embodiment of the reservoir  30  on which the invention is based can be seen in  FIG. 1  from the switching symbol and will be made clear below in conjunction with the description of  FIGS. 2 through 5 . With regard to the connection of the reservoir  30  to the hydraulic circuit, it can be seen from  FIG. 1  that a reservoir  30  according to the invention, for its supply with pressure fluid, now has at least one inlet  44  and at least one outlet  46  that is embodied separately from the inlet  44 . As the check valve  32 , which is disposed between the pump  26  and the reservoir  30 , a check valve  32  without a restoring spring is used according to  FIG. 1 . The absent restoring spring is covered in the applicable claims by the wording “check valve with a freely movably received valve closing body”. 
       FIG. 2  shows a detail of the aforementioned hydraulic block  40  of the hydraulic unit  18 , with a reservoir  30  embodied according to the invention. The reservoir housing of this reservoir  30  is formed by the wall of a bore  50  which is stepped off multiple times from the outside inward and which leads from the underside  52  into the interior of the hydraulic block  40 . The bore  50  is broken down into one outer cylindrical peripheral portion  54 , an adjoining introduction portion  57  tapering conically inward, and an inner cylindrical fastening portion  58 . This fastening portion  58  ends in a horizontally extending stop shoulder  60 , in the center of which an outlet  46  discharges outward. 
       FIG. 2  shows a detail of the aforementioned hydraulic block  40  of the hydraulic unit  18 , with a reservoir  30  embodied according to the invention. The reservoir housing of this reservoir  30  is formed by the wall of a bore  50  which is stepped off multiple times from the outside inward and which leads from the underside  52  into the interior of the hydraulic block  40 . The bore  50  is broken down into one outer cylindrical peripheral portion  54 , an adjoining introduction portion  56  tapering conically inward, and an inner cylindrical fastening portion  58 . This fastening portion  58  ends in a horizontally extending stop shoulder  60 , in the center of which the outlet  46  discharges outward. 
     A cup-shaped support element  62 , which can for instance be made by deep-drawing from a sheet-metal blank, is press-fitted into the fastening portion  58 . The opening  64  of the support element points in the direction of the outlet  46  and is completely covered by an elastic diaphragm  66  of pressure fluid-resistant material. This diaphragm  66  is crimped along its outer circumference to the support element  62 , and the circumference of the support element  62  that is created by the crimping serves simultaneously to anchor this support element  62  by nonpositive engagement in the fastening portion  58 . A sealing plate  68  rests on the outside, toward the outlet  46 , of the diaphragm  66 . This sealing plate is joined by positive engagement to the diaphragm  66 , specifically with the aid of a knob  70  protruding in the direction of the outlet  46 . The knob  70  penetrates a recess in the center of the sealing plate  68  and with its thickened head engages the recess from behind. The sealing plate  68  covers the cross section of the outlet  46  completely, but it has a smaller outer diameter compared to the inner diameter of an opening  64  in the support element  62 . As a result, between the inner end of the crimping and the sealing plate  68 , an annular chamber  72  is created, defined in the axial direction by the diaphragm  66  and the stop shoulder  60 . It must be assumed that the at least one inlet  44  ( FIG. 1 ) of the reservoir  30 , arriving from the wheel brake  16  ( FIG. 1 ), discharges into this annular chamber  72 . 
     The diaphragm  66 , together with the sealing plate  68 , forms a separator element that is received freely movably in the support element  62  and that seals off a (second), gas-filled storage chamber  74 , disposed in the interior of the support element  62 , from a (first) storage chamber  76  that can be filled with hydraulic pressure fluid of the vehicle brake system. This first storage chamber  76  is located between the sealing plate  68  and the check valve  32 , the check valve being placed axially spaced apart from the sealing plate  68  in the outlet  46  of the reservoir  30 . It increases its volume when pressure fluid flows in, because the sealing plate  68  lifts from the stop shoulder  60  and moves into the interior of the support element  62 . To a corresponding extent, the volume of the storage chamber  74  decreases. 
     The aforementioned check valve  32  comprises a valve seat part  80 , in the form of a perforated disk which is press-fitted into the outlet  46  until it stops against a shoulder  82 . The valve seat part  80  cooperates with a valve closing body  84 , here shown in the form of a ball as an example. The ball is received freely movably, downstream of the valve seat part  80 , in a cylinder portion  86  of the outlet  46  and controls a conically shaped valve seat  88  on the inside of the perforated disk. A constriction  90  of the outlet  46 , embodied downstream of the cylindrical portion  86 , forms the connection of the check valve  32  to an intake side of the pump  26  (see  FIG. 1 ). At the constriction  90 , star-shaped ribs or grooves  92  extending outward are preferably present, which assure a flow around the valve closing body  84  even whenever the valve closing body is in contact with the constriction  90 . Accordingly, there can be a flow through the check valve  32  described only in the direction toward the pump  26 , while this check valve blocks off the flow in the opposite direction, toward the reservoir  30 . 
     The view in  FIG. 2  shows the reservoir  30  with the first storage chamber  76  emptied. Accordingly, the freely movable separator element (diaphragm  66 ) assumes its first end position. In that position, the sealing plate  68  rests on the stop shoulder  60  of the bore  50  and seals off the inlet  44  from the outlet  46 . Underpressure, generated by the self-aspirating pump  26  connected to the outlet  46 , can as a result not reach the inlet  44  and thus cannot reach the wheel brakes  16  connected to it. The aspirating pump  26  is accordingly supplied with pressure fluid from the master cylinder  14  only via the opened multi-way valve  20  ( FIG. 1 ). The check valve  32  described prevents pressure fluid under pressure, in the event of pedal actuation during an ongoing traction control operation, from flowing into the reservoir  30  from the master cylinder  14  when the valve  20  is open. 
       FIG. 3  shows an alternative embodiment of a reservoir  30 . Its reservoir housing is again formed by the wall of a bore  50 , open toward the outside, of the hydraulic block  40 . This reservoir  30  includes a cup-shaped support element  94 , which is press-fitted with its open end leading into the bore  50 . The support element  94  is recessed in its outer diameter in the region of its opening, and as a result an annular chamber is created between the circumference of the support element  94  and the inner wall of the bore  50 . In this annular chamber is a sealing portion  98  of a roll diaphragm  100 ; the sealing portion encircles the circumference of the support element  94 . This roll diaphragm  100  is as a result held in the hydraulic block  40  by positive engagement between the support element  94  and the inner wall of the bore  50 . It covers the entire opening of the support element  94 , forming a diaphragm fold  102 , which extends into the hollow interior of the support element  94 , and a central portion  104 , which integrally adjoins the diaphragm fold  102 . With its central portion  104 , the roll diaphragm  100  protrudes axially relative to the encircling sealing portion  98 , and on the face end of its central portion  104 , it has a control cross section  106 . This separator element (or roll diaphragm  100 ) divides a gas-filled (second) storage chamber  74 , enclosed between it and the support element  94 , from a first storage chamber  76  that can be filled with pressure fluid. The first storage chamber  76  is located between the roll diaphragm  100  and a check valve  32  disposed in the outlet  46 . The check valve used is essentially equivalent in its embodiment to the check valve  32  described in conjunction with  FIG. 2 . One difference is that the check valve  32  here is embodied as a component unit, with its own valve housing, that can be anchored in the hydraulic block  40 . Upstream of the valve closing body  84 , the valve housing is provided with openings, through which, when the valve seat  88  is open, pressure fluid can flow past the valve closing body  84  to the outlet  46 . 
     The roll diaphragm  100  is likewise received freely movably between two end positions. In the first end position, shown, the pressure fluid-filled first storage chamber  76  has been emptied completely. The roll diaphragm  100  now rests with its control cross section  106  on the side of the valve seat part  80  diametrically opposite the valve seat  88  of the check valve  32 . Thus the roll diaphragm  100  seals off the inflow cross section of the check valve  32  and blocks any communication from the inlet  44  of the reservoir  30  to the outlet  46 . The inlet  44  cannot be seen in  FIG. 3 , but it opens into the region of the diaphragm fold  102 . Consequently, here as well, the buildup of the underpressure effected by the driven pump  26  connected to the outlet  46  in the wheel brakes  16  contacted by the inlet  44  is prevented. 
     In the exemplary embodiment of  FIG. 4 , the reservoir  30  is embodied as a screw-on version. For this purpose, its reservoir housing  31  is embodied as a separate component that is screwed into the hydraulic block  40 . In the reservoir housing  31 , a cylindrical bore  50  receives a hollow piston  110 . This piston is installed, with its opening leading, until it comes to a stop in the reservoir housing  31 . This opening in the hollow piston  110  is spanned by a diaphragm  66 , which rests on the face end of the wall  112  surrounding the opening. The hollow piston  110 , on its end remote from the diaphragm  66 , is provided with a radially protruding collar  114 . This collar  114  rests on an inversely shaped recess in the bore  50 . A closure stopper  94 , which can be screwed into the bore  50  from outside, exerts an axial force on the hollow piston  110 . As a result of the screwing-in torque of the closure stopper  94 , the diaphragm  66  is fixed between the hollow cylinder and the stop shoulder  60  ( FIG. 2 ) of the bore  50 . The inlet  44  and the outlet  46  of this reservoir  30  extend parallel to one another in the screw-in stub of the reservoir housing  31 . The result at its orifice into the bore  50  is a rib  116 , which cooperates with the diaphragm  66 . The view in  FIG. 4  shows the diaphragm  66  in one end position again. The diaphragm  66  acts as a separator element between the two storage chambers  74  and  76  and simultaneously, in the end position shown, blocks off the communication from the inlet  44  to the outlet  46 . In this exemplary embodiment again, a check valve  32  with a freely movable valve closing body  84  is located in the outlet  46 , as has already been disclosed in conjunction with  FIG. 2 . 
       FIG. 5  shows a further exemplary embodiment of a reservoir  30 , in which a hollow piston  120  is used as the separator element. This piston  120  is made from thin-walled, rigid material and has a piston bottom  122  with a centrally protruding protrusion  124 . The hollow piston  120  is guided movably in a bore  50  and is sealed off on its circumference by a conventional sealing element  126 , such as an O-ring or a quad ring. The installation direction of the piston  20  is such that the piston bottom  122  is oriented toward the outlet  46  of the reservoir  30 , and the open end of the piston  120  points in the direction of the opening of the bore  50  of the hydraulic block  40 . This opening is closed by a closure cap  128 . The closure cap  128  is embodied as cup-shaped, and its inside diameter is equivalent to the inside diameter of the bore  50  of the hydraulic block  40 . As a result, the piston  120  can penetrate into the interior of the closure cap  128 . The end face, located inside the reservoir  30 , of the closure cap  128 , together with an axial shoulder  130  of the hydraulic block  40 , keeps the sealing element  126  that seals off the piston  120  in position. The closure cap  128  can be held on the hydraulic block  40  by nonpositive engagement, such as press-fitting, or positive engagement, such as calking. 
     In this exemplary embodiment, the rigid piston  120  acts as a separator element between two storage chambers  74  and  76 . The first storage chamber  76 , which can be filled with the hydraulic pressure fluid of the vehicle brake system, is embodied between the piston bottom  122  and the check valve  32 ; the second, gas-filled storage chamber  74  is defined by the interior of the piston  120  and by the closure cap  128 . In the position shown, the first storage chamber  76  has essentially been emptied of hydraulic pressure fluid, and as a result, the piston  120  with the protrusion  124  from its piston bottom  122  seals off the inflow cross section of the check valve  32 . Since in this exemplary embodiment as well it must be assumed that the inlet  44 , not shown, discharges into the first storage chamber  76 , the piston  120  in the end position shown thus also blocks off the pressure fluid-conducting connection from the inlet  44  to the outlet  46 . 
       FIG. 6  shows the relative position of the inlets and outlets  44 ,  46  of a reservoir  30  in a cross section through the reservoir  30  in the region of the orifice cross sections of these conduits. A total of three orifice cross sections can be seen in  FIG. 6 , of which two form inlets  44  and one forms an outlet  46 . The outlet  46  is located in the center of the cross sections shown; the two inlets  44  are placed symmetrically to both sides of this outlet  46 . All three orifice cross sections are located on a common line  132 . 
     For bleeding the vehicle brake system  10  in  FIG. 1 , pressure fluid under pressure is fed into the various lines  34  via the connection of a wheel brake  16 . Via the electronic control unit  42 , the multi-way valves  22 , which are closed in their basic position, are triggered and switched to their open position. The fed-in pressure fluid flows into the storage chamber  76  via the inlet  44  and causes a deflection of the respective separator element  66 ;  100 ;  110 ;  120  into the second end position, not shown. In the process, the separator element  66 ;  100 ;  110 ;  120  opens a communication from the inlet  44  to the outlet  46  of the reservoir  30 , so that the pressure fluid flows onward in the direction of the pump  26 , via the check valve  32  that is open in the flow direction. The pressure fluid flow branches off upstream of a pump  26  into a first branch, which leads to the master cylinder  14  via the triggered multi-way valve  22 , and a second branch, which also leads to the master cylinder  14 , but through the non-triggered multi-way valve  20 . Hence there are no regions of the vehicle brake system  10  through which pressure fluid does not flow. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.