Abstract:
A brake booster, in particular for motor vehicles, having a control valve for controlling the boosting force generated by the brake booster. The control valve comprises a control valve housing, an input element, an output element and a thrust piece, which is disposed between the input element and the output element and acts upon the output element. The thrust piece in dependence upon a relative movement between the thrust piece and the control valve housing caused by the input element is supported releasably against the control valve housing by means of a coupling element biased by a spring. The spring and the coupling element are designed as an integral coupling component, which is fastened to the control valve housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of International Application No. PCT/EP03/08318 filed Jul. 28, 2003, the disclosures of which are incorporated herein by reference, and which claimed priority to German Patent Application No. 102 34 693.3 filed Jul. 30, 2002, the disclosures of which are incorporated herein by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   REFERENCE TO A “MICROFICHE APPENDIX” 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to brake boosters, in particular for motor vehicles, according to the preamble of claim  1 , such as are known e.g. from WO 99/26826. Such brake boosters generally take the form of vacuum brake boosters and are used during braking to provide the driver of a vehicle with an auxiliary force so that the brake actuating force to be summoned up by the driver may be kept to a comfortable level. Purely hydraulically operating brake boosters are also known and the present invention is therefore not restricted to vacuum brake boosters. 
   2. Description of Related Art Including Information Described Under 37 CFR 1.97 and 1.98 
   Irrespective of the manner in which the auxiliary force is generated, e.g. by means of a vacuum or hydraulically, a brake booster usually has a control valve for controlling the boosting force it generates, i.e. the amount of auxiliary force, as well as a control valve housing. Extending at least partially into the control valve housing is an input element, with the aid of which a braking request of the driver is communicated to the brake booster. The input force, which is introduced via the input element into the brake booster, and the auxiliary force, which is subsequently generated by the brake booster, are combined at an output element and delivered by the output element to a master cylinder, connected downstream of the brake booster, of a vehicle hydraulic brake system. If the brake booster is a vacuum brake booster, the output element generally comprises a rubber-elastic material in disk form, which is disposed in a chamber in an end piece of the control valve housing and behaves like a liquid. Situated between the output element and the input element is a thrust piece, which is movable axially relative to the control valve housing. The actuating force introduced into a brake booster therefore flows via the input element and from there, optionally via interposed components such as valve pistons or the like, to the thrust piece and then to the output element. 
   It has already been known for some time that most drivers of a motor vehicle in an emergency braking situation do not actuate the brake strongly enough. This behaviour is disadvantageous particularly if the vehicle brake system is equipped with an anti-skid system, because the maximum braking action of a brake system equipped with an anti-skid system may be achieved only when each vehicle wheel during braking enters a slip-controlled state, i.e. when each vehicle wheel is braked to such an extent that the slip control of the anti-skid system is activated. This state is reached only when a sufficiently high hydraulic actuating pressure is supplied to each vehicle wheel, this in practice frequently not being the case. 
   As a solution to this problem, a device mostly described in technical literature as “brake assistance” is proposed. To put it concisely, this brake assistance ensures that in an emergency braking situation, i.e. when the input element is moved very quickly a relatively long way in the actuating direction, the brake booster provides its maximum auxiliary force. Early brake assistance solutions employed an electromagnet which, after identification of an emergency braking situation, independently of the actual input force held the air control valve of a vacuum brake booster in the open position so that the maximum pressure difference between a vacuum chamber and a working chamber and hence the maximum possible auxiliary force was able to build up in the vacuum brake booster. In order to achieve the same effect without an expensive electromagnet, later solutions propose that the previously mentioned thrust piece be supported in an emergency braking situation against the control valve housing so that the hydraulic reaction forces transmitted from the master cylinder back into the brake booster do not retroact upon the input element of the brake booster and hence upon the brake pedal but are taken up by the brake booster. Thus, with a relatively low input and/or actuating force a high output force may be achieved, this being desirable in an emergency braking situation. Solutions of the last-described type are known from the previously mentioned WO 99/26826 and from EP 0 901 950 B1. 
   The last-mentioned solutions are however mechanically relatively complex and therefore not much less expensive than the likewise mentioned electromagnetic solution. 
   BRIEF SUMMARY OF THE INVENTION 
   The underlying object of the invention is therefore to provide a brake booster with brake assist function, which is mechanically simpler and hence less expensive than previously known solutions. 
   Proceeding from the initially mentioned background art, which effects the supporting of the thrust piece in that by releasably supporting the thrust piece against the control valve housing by means of a coupling element biased by a spring, this object is achieved according to the invention in that the spring and the coupling element are designed as an integral coupling component, which is fastened to the control valve housing. Thus, without impairing the desired function, a markedly reduced complexity of the mechanical construction and hence a perceptible cost reduction is achieved. 
   According to a preferred development of the invention, the coupling component has a substantially hollow cylindrical shape and concentrically surrounds a valve piston, which is workingly connected to the input element and the thrust piece. Formed on the valve piston, which as a rule is connected directly to the input element, is a valve seat, the so-called atmosphere sealing seat, the opening of which by means of a displacement of the input element in actuating direction leads to a flow of atmospheric pressure into the working chamber of a vacuum brake booster and consequently to the build-up of a boosting force. The arrangement of a hollow cylindrical coupling component around such a valve piston not only saves space but is also functionally advantageous. 
   In preferred forms of construction of the brake booster according to the invention, the coupling component tapers conically in the direction of the thrust piece. In such embodiements, the coupling component in the region of its conical taper preferably has a plurality of spring tongues biased in a radially inward direction. Given such a form of construction, the spring tongues perform both the spring bias function and the coupling function. 
   In forms of construction with a coupling component that has spring tongues biased in a radially inward direction, the free ends of the spring tongues preferably cooperate in a sliding manner with a detent sleeve, which is disposed displaceably on the valve piston. The one end of the detent sleeve is in said case designed so that it may be supported against the valve piston, while the other detent sleeve end is designed so that it may be supported against the thrust piece. In order that such a detent sleeve may be locked against return displacement relative to the control valve housing and at the same time be supported against the control valve housing, with the result that the thrust piece supported against the detent sleeve is also locked and supported in the same manner, the detent sleeve preferably comprises a detent collar, behind which the free ends of the spring tongues latch when a predetermined displacement of the thrust piece relative to the control valve housing in the direction of the output element is exceeded. In a simple form of construction, the detent collar may be formed e.g. by a stepped taper of the outside diameter of the detent sleeve. 
   In another form of construction, the detent collar is a projection projecting in a radially outward direction from the outer peripheral surface of the detent sleeve and preferably designed circumferentially as an annular collar. The detent sleeve and the thrust piece, which have been described here as two separate parts, may alternatively be integrally connected to one another. Also, the detent sleeve need not be disposed on the valve piston but may adjoin the valve piston in actuating direction, i.e. be disposed between the valve piston and the thrust piece and, if desired, formed integrally with the thrust piece. The “detent sleeve” then also need no longer be a sleeve but may be made of solid material like the thrust piece. 
   In a preferred form of construction of the brake booster according to the invention, in order to be able to release the previously described latching state there is displaceably disposed on the valve piston a decoupling sleeve, of which one end facing the input element is designed to be supportable against a transverse locking bar connected to the valve piston and the other end is designed, upon a displacement of the control valve housing relative to the decoupling sleeve in the direction of the input element, to come into contact with the coupling component and press the free ends of the spring tongues radially outwards in order to release the latter from their latched position behind the detent collar of the detent sleeve. In order to be able to carry out this task, the decoupling sleeve has to be of a sufficiently rigid construction, i.e. it has to be easily able to withstand the radially inwardly directed spring bias of the coupling component. The end of the decoupling sleeve facing the coupling component is preferably annular, if the coupling component is hollow cylindrical. 
   In all forms of construction of the brake booster according to the invention, the coupling component is preferably made of spring steel. It is thereby guaranteed that the coupling component, on the one hand, generates the desired spring bias and, on the other hand, is capable of transmitting the supporting forces to the control valve housing without itself being destroyed. 
   For the stationary anchoring of the coupling component in the control valve housing, the coupling component at its end facing the input element is preferably provided with a radially outwardly projecting flange, which may engage behind a projection formed in the control valve housing, so that the flange is fixed in the control valve housing by means of a snap ring, which is inserted into an adjacent groove of the control valve housing. In order to increase the stability of the coupling component vis-à-vis a deformation brought about by transmission forces, a portion of the coupling component extending from the radially outwardly projecting flange in the direction of the free end of the coupling component has an outside diameter, which apart from normal tolerances corresponds to the inside diameter of a bore of the control valve housing, in which bore said portion of the coupling component is disposed. This allows the said portion to be supported against the wall of the bore in the control valve housing without leading to a deformation of the coupling component. Given such a construction, the wall thickness of the said portion of the coupling component need not be made as thick as would otherwise be necessary. 
   Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  shows in longitudinal section the presently relevant part of a vacuum brake booster, generally denoted by  10 , for a motor vehicle hydraulic brake system. The brake booster  10 , downstream of which a master brake cylinder (not shown here) is connected, has a housing  12  of sheet-metal shells, only the beginning of which is shown in the drawing and in which a non-illustrated movable wall separates and seals off a working chamber  14  from a vacuum chamber  16 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The movable wall is firmly connected to a control valve housing  18 , which extends in a sliding, displaceable manner in a tubular end portion  20  of the brake booster housing  12 . The control valve housing  18  is part of a control valve  22  for selectively connecting either the working chamber  14  to the ambient atmosphere or the vacuum chamber  16  to the working chamber  14 . 
   During operation of the brake booster  10  the vacuum chamber  16  is constantly connected to a vacuum source, e.g. the intake manifold of an internal combustion engine, in order to continuously maintain in the vacuum chamber a pressure lower than the ambient atmosphere. In an initial state of the brake booster  10 , the working chamber  14  is also evacuated to this lower pressure. If the control valve  22  is then actuated by applying an input force F to an input element  24 , the input element  24  and a valve piston  26  workingly connected thereto are displaced into the brake booster housing  12 , i.e. to the left in the drawing. An annular atmosphere sealing seat  28  formed on the valve piston  26  therefore lifts off an annular valve sealing element  30  and therefore allows atmospheric pressure to flow through a filter  32  into the control valve housing  18  and past the now open atmosphere sealing seat  28  into the working chamber  14 . At the movable wall separating the working chamber  14  from the vacuum chamber  16  a pressure difference therefore builds up, and the force resulting therefrom then endeavours to displace the movable wall and the control valve housing  18  firmly connected thereto to the left. This force is the auxiliary or servo force generated by the brake booster  10 . It is delivered via a rubber-elastic output element  34 , which is disposed in a chamber in an end portion of the control valve housing  18  facing the master cylinder, to the master cylinder, e.g. with the aid of an only partially illustrated tappet  36 . 
   Disposed in an axially displaceable manner between the rubber-elastic output element  34  and the valve piston  26  is a thrust piece  38 , via which the input force F applied to the input element  24  is transmitted to the output element  34 . In the output element  34 , therefore, the input force F applied by a user and the auxiliary force generated by the brake booster  10  are combined and then delivered to the master cylinder. 
   When the user releases the brake, the valve piston  26  moves back to the right, strikes against the valve sealing element  30  and presses it slightly to the right so that the valve sealing element  30  lifts off an annular vacuum sealing seat  40  formed in the control valve housing  18 , with the result that a connection is established between the vacuum chamber  16  and the working chamber  14  and the working chamber  14  is evacuated once more in order to re-establish the initial state needed at the start of a braking operation. This general function of a vacuum brake booster is well known to experts in this field and therefore requires no further explanation. 
   To provide a so-called brake assist function, in the control valve  22  further components are disposed, which are described in detail below. Here, “brake assist function” means that the brake booster  10  in an emergency braking situation provides a user with the maximum brake power assistance, i.e. the maximum auxiliary force, even if the user does not maintain a corresponding input force F or at any rate does not maintain it throughout the braking operation. During a normal braking operation, as described, the valve piston  26  is displaced relative to the control valve housing  18 . On an end portion  42  of the valve piston  26  facing the output element  34  and having a reduced diameter a detent sleeve  44  having a radially outwardly projecting annular flange  45  is disposed in a floating manner, which detent sleeve in contrast to the form of construction illustrated here may alternatively be formed integrally with the thrust piece  38 . The end of the detent sleeve  44  facing the input element  24  is supported against a step  46  formed on the valve piston  26  by the diameter reduction, so that the detent sleeve  44  upon an actuation of the brake booster  10  is driven by the valve piston  26  to the left. The opposite, other end of the detent sleeve  44  terminates flush with the associated end of the valve piston  26  and, like this end, is in contact with the thrust piece  38 . 
   Formed on the outer peripheral surface of the detent sleeve  44  is a detent collar  48 , which in the present case is continuous in peripheral direction and the function of which is described in greater detail below. 
   Disposed in a bore  50  of the control valve housing  18  is a generally hollow cylindrical coupling component  52 , which in the present case is made of spring steel. At its end facing the input element  24  the coupling component  52  has a radially outwardly projecting flange  54 , which engages behind a stepped projection  56  in the bore  50 . Formed adjacent to the projection  56  in the wall of the bore  50  is an annular groove  58 , into which is inserted a snap ring  60 , which fastens the flange  54  of the coupling component  52  in the control valve housing  18 . 
   Adjoining the flange  54  is a portion  62  of the coupling component  52 , which portion extends in the direction of the output element  34  and has an outside diameter, which apart from normal tolerances corresponds to the inside diameter of the bore  50 . With this portion  62  the coupling component  52  may be supported against the wall of the bore  50 . The coupling component  52  tapers conically towards its free end. The region of the conical taper is formed by a plurality of spring tongues  64 , which are biased in a radially inward direction and separated from one another by non-illustrated slots and the free ends of which rest on the surface of the detent collar  48 . 
   A decoupling sleeve  68  is disposed in an axially displaceable manner on a portion  66  of the valve piston  26  and may be supported by its, in the present case, flange-like end facing the input element  24  against a transverse locking bar  70 , which is connected to the valve piston  26  and is axially displaceable in a groove  71  of the valve piston  26 . The transverse locking bar  70  is used to define an initial position of the control valve  22  in that its free end in the initial position is supported against a stop  72  of the brake booster housing  12 . This initial position is also referred to as the LTF position (lost-travel-free position). From this initial position, the brake booster  10  is actuable without lost travel. 
   As already explained, during a normal braking operation the valve piston  26  is displaced relative to the control valve housing  18 , thereby opening the atmosphere sealing seat  28 , and in said case drives the detent sleeve  44 . Both the detent sleeve  44  and the valve piston  26  press upon the thrust piece  38 , which is likewise displaced relative to the control valve housing  18  and penetrates into the rubber-elastic output element  34 . The spring tongues  64 , which in the initial state shown in the drawing rest on the annular free end of the decoupling sleeve  68 , in said case retain the decoupling sleeve  68  and hence the transverse locking bar  70  accommodated in a floating manner in the groove  71 . By virtue of the build-up of the corresponding auxiliary force in the brake booster  10 , the control valve housing  18  follows and the transverse locking bar  70  detaches itself from the stop  72  on the brake booster housing  12 . If a user of the brake booster  10  does not further increase the input force F, a state of equilibrium associated with the respective braking intensity sets in, in which the atmosphere sealing seat  28  once more lies against the valve sealing element  30 . During such a normal braking operation, the surface of the detent collar  48  only moves to and fro under the free ends of the spring tongues  64  because the relative displacement of the detent sleeve  44  during a normal braking operation is smaller than the extension of the surface of the detent collar  48  in axial direction. 
   It is only when the displacement of the valve piston  26  and hence of the detent sleeve  44  relative to the control valve housing  18  is greater and exceeds a predetermined value, as is the case e.g. during an emergency braking operation, that the surface of the detent collar  48  is moved away from the region under the free ends of the spring tongues  64  and the spring tongues  64  by virtue of their radially inwardly acting spring bias press the decoupling sleeve  68  slightly back in the direction of the input element  24 , i.e. to the right in the drawing, with the result that the transverse locking bar  70  is also correspondingly displaced in the groove  71  in the valve piston  26 . The free ends of the spring tongues  64  snap behind the detent collar  48  and therefore couple the detent sleeve  44  substantially rigidly to the control valve housing  18 . The effect of this coupling is that now all of the reaction forces retroacting from the hydraulic brake system no longer act upon the valve piston  26  and hence via the input element  24  upon the brake pedal but are introduced via the thrust piece  38 , the detent sleeve  44  and coupling component  52  into the control valve housing  18 . This means that all of the reaction forces are absorbed by the brake booster  10  alone, unless the user of the brake booster  10  presses upon the input element  24  powerfully enough for the valve piston  26  to rest against the thrust piece  38 . In this state, the atmosphere sealing seat  28  may therefore be held open without the user of the brake booster  10  having to overcome significant counterforces. In other words, this state corresponds to a change of the force transmission ratio of the brake booster  10  towards infinity. 
   The maximum possible displacement of the valve piston  26  relative to the control valve housing  18  is defined by the axial distance of the annular flange  45  of the detent sleeve  44  from the base of the bore  50 . This distance is smaller than the axial extension of the groove  71  in the valve piston  26 . 
   When a user of the brake booster  10  wishes to terminate an emergency braking operation, in the course of which the described rigid coupling of the thrust piece  38  to the control valve housing  18  has occurred, he reduces the input force F exerted upon the input element  24  in a corresponding manner, whereupon the valve piston  26  separates from the thrust piece  38 , the atmosphere sealing seat  28  is reapplied against the valve sealing element  30  and the latter shifts counter to actuating direction slightly to the right, with the result that the vacuum sealing seat  40  lifts off the valve sealing element  30  and a connection is established between the working chamber  14  and the vacuum chamber  16 . As a result of this connection, the pressure difference at the non-illustrated movable wall of the brake booster  10  is reduced and the control valve housing  18  moves back to the right. As soon as the transverse locking bar  70  is supported against the stop  72 , the decoupling sleeve  68  is also unable to move further to the right so that, upon a further return stroke of the control valve housing  18 , the annular free end of the decoupling sleeve  68  strikes from the inside against the spring tongues  64  and pushes them radially outwards. In other words, the inner surfaces of the spring tongues  64  run onto the end of the decoupling sleeve  68  and, upon a further return motion of the control valve housing  18 , are then inevitably pushed radially outwards. The latching state is thereby released and the surface of the detent collar  48  moves once more to a point under the free ends of the spring tongues  64 . 
   In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.