Abstract:
The present invention relates to a brake force booster with a panic braking function for automotive vehicles. The present invention includes that the first sealing seat arranged movably in relation to the control housing wherein the sealing seat is fixed to a lever such that when a predetermined relative displacement between valve piston and control housing is exceeded so that the lever prevents at least a movement of the sealing seat in the actuating direction. The brake force booster with a brake assist function is easy to manufacture and, in addition, ensures a controllability of the brake force in the emergency braking position.

Description:
TECHNICAL FIELD 
     The present invention generally relates to vehicle brake systems and more particularly relates to a brake force booster with a panic braking function for automotive vehicles. 
     BACKGROUND OF THE INVENTION 
     A brake force booster of this general type is disclosed in U.S. Pat. No. 5,645,145. During actuation, the valve piston of the prior art brake force booster interacts with a hydraulic piston which defines a first hydraulic chamber along with a force output member or a push rod. On the side of the hydraulic piston remote from the first chamber, there is a second hydraulic chamber which is connected to the first chamber by way of a plurality of channels, and the connection is closable by means of a valve assembly. A second hydraulic piston or annular piston is axially supported on the hydraulic piston, under the preload of a compression spring, the said piston permitting displacement of the fluid volume from the second chamber into the first chamber. Consequently, the described arrangement represents a hydraulic reaction device. The above-mentioned valve assembly is preferably configured so that it remains closed during ‘normal’ operation so that a transmission of the actuating force introduced at the valve piston and of the boosting force raised by the brake force booster occurs by means of the fluid volume enclosed in the first chamber. When a rapid actuation takes place, which is e.g. due to panic braking or emergency braking, the valve assembly remains open so that the fluid is displaced from the first chamber into the second chamber and the valve piston that is supported on the first hydraulic piston can cover a longer actuating travel, which causes an increase of the slot between the second sealing seat and a valve member and, thus, a quicker ventilation of the ventilatable working chamber of the prior art brake force booster. 
     The state of the art brake force booster especially suffers from the disadvantage of the complicated design of the mentioned means or the reaction device, whose chambers must be sealed by means of sealing elements which cause an increase of the friction developing in the system and, further, represent a potential source of disturbance. Further problems are involved with filling the hydraulic chamber with liquid pressure fluid, which is in particular inappropriate for large-scale production. 
     An object of the present invention is to disclose provisions which increase the reliability in operation and extend the useful life of the brake force booster. Another objective is to permit manufacture of the brake force booster disclosed by reasonable efforts. 
     According to the present invention, this object is achieved because the first sealing seat is arranged movably in relation to the control housing, and there is provision of a means by which the sealing seat can be fixed in position when a predetermined relative displacement between the valve piston and the control housing is exceeded so that the means permits a movement of the sealing seat in opposition to the actuating direction relative to the control housing. Consequently, decrease of the slot at the second sealing seat, the so-called poppet valve, which could be caused by movement of the sealing seat in the actuating direction is prevented. 
     To specify the idea of the present invention, it is provided that the first sealing seat is supported indirectly or directly on a reaction disc when the predetermined relative displacement between the valve piston and the control housing is exceeded. Thus, in the actuated condition, the deformation of the reaction disc causes the sealing seat to lift from its stop that is active in the actuating direction, and namely in opposition to the forces of a resetting spring. 
     In a preferred aspect of the present invention, a sleeve is associated with the valve piston in a way axially displaceable in relation thereto, the said sleeve including a stop as mentioned above, and the sealing seat, due to abutment on the stop, is supported on the reaction disc by means of the sleeve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged cross-sectional view, partly broken away, of the brake force booster of the present invention in the inactive ready position. 
     FIG. 2 shows the control assembly of the brake force booster according to FIG. 1 in an active emergency braking position (panic braking position). 
     FIG. 3 is a view of the control assembly shown in FIG. 2 in a return stroke position, i.e., after removal of the actuating force. 
     FIG. 4 is a view of the control assembly of the brake force booster according to FIG. 1 in the brake&#39;s fully applied position (maximum force). 
     FIG. 5 is a cross-sectional view, as in FIG. 1, of a second embodiment of the present invention. 
     FIG. 6 is a cross-section taken along line VI—VI in FIG.  5 . 
     FIG. 7 is a cross-section taken along line VII—VII in FIG.  5 . 
     FIG. 8 is a cross-section as in FIG. 7, taken along line VIII—VIII in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The booster housing  1  (shown only schematically) of the vacuum brake force booster of the present invention, as illustrated in the drawings, is subdivided into a first chamber  2  (vacuum chamber) and a second chamber  3  (working chamber) by an axially movable wall. The axially movable wall (not shown) is comprised of a diaphragm plate and a flexible diaphragm  4  which abuts thereon (indicated only in part) and is configured as a rolling diaphragm to provide a sealing between the outside periphery of the diaphragm plate and the booster housing  1  (not shown in detail). 
     A control valve  5  operable by an actuating rod  7  is accommodated in a control housing  8 , that is sealed and guided in the booster housing  1  and carries the movable wall, the said control valve having a first sealing seat  15  which is movable axially relative to the control housing  8  and is guided therein. In addition, the actuating rod  7  is rigidly connected to a valve piston  6  on which a second sealing seat  16  is provided. Further, the valve assembly comprises a valve member  10  which cooperates with both sealing seats  15 ,  16  and is sealedly arranged in the control housing  8 , the said valve member being urged against the valve seats  15 ,  16  by means of a valve spring  22  supported on a bottom  21 . The working chamber  3  is connectable to the vacuum chamber  2  by way of a channel  29  that extends laterally in the control housing  8 . 
     By way of a rubber-elastic reaction disc  9  that abuts frontally on a front part  14  of the control housing  8 , and a push rod  12  that has a head flange  13 , the brake force is transmitted to an actuating piston of a (non-illustrated) master cylinder of the brake system which is fitted to the vacuum-side booster housing half. A central opening in the front part  14  serves for the passage of a pressure member with a preferably conical pressure surface so that the driver can boost the effect of force, produced by the pressure difference by way of the front part, by additionally applying the pressure member which is movable into abutment on the front side of the valve piston  6 . 
     A resetting spring  17 , shown schematically in the drawing, which is supported on the vacuum-side end wall of the booster housing  1  retains the movable wall in the initial position shown. There is further provision of a second compression spring or piston rod return spring  18  which is supported indirectly on the actuating rod  7 , on the one hand, and on the bottom  21 , on the other hand, and the force of which ensures a bias of the valve piston  6  or its sealing seat  16  in relation to the valve member  10 . 
     To connect the working chamber  3  to the atmosphere when the control valve  5  is actuated, a channel  19  which extends roughly radially is still designed in the control housing  8 . The return movement of the valve piston  6  at the end of a braking operation is limited by a transverse member  11  which bears against a stop  20  provided in the booster housing  1  in the ready position of the vacuum brake force booster shown in FIG.  1 . 
     As can further be taken from the drawings, the valve member  10  includes an annular sealing surface  23  which cooperates with the two sealing seats  15 ,  16 . Sealing surface  23  is reinforced by means a metal reinforcing disc  24  and includes a number of axial passages for pressure compensation. For pressure compensation purposes, a guide member, instead of the bottom  21 , may be provided in which the valve member  10  is guided and movable, sealed by sealing lips, so that a pressure-balanced pneumatic chamber for the valve member  10  is produced inside the control housing  8 . EP 655 039 A1 is referred to in full extent as far as this modification is concerned. This arrangement consequently permits a reduction of the difference between the response force of the brake force booster and the resetting force acting on the valve piston to the end that with a constant response force, an increase of the resetting force is possible, or a reduction of the response force is possible with a constant resetting force. 
     As can further be clearly seen in FIG. 1, a means  26  is associated with the sealing seat  15  and permits determining said&#39;s position when a predefined relative displacement between valve piston  6  and control housing  8  is exceeded. For this purpose, the valve piston  6  on the end close to the reaction disc has a sleeve  32  which is displaceable coaxially relative to the valve piston  6  and movable into abutment on a shoulder  31  close to the valve piston. Upon actuation, sleeve  32  along with the piston  6  is displaced in the direction of the pressure member  27 . Sleeve  32  is provided with a stop  36  on which means  26  can engage with a projection  36 , as can be seen in FIGS. 2 and 3. According to the said embodiment, a lever is used as the means which is swivellably articulated at the sealing seat  15  or a base member  25  that carries the sealing seat by means of a knife-edge support or a pin  33 . The lever has the shape of an L, when viewed from the side, and includes a first leg  34  and a second leg  35  (hinted at). A projection  36  is arranged on the second leg  35  for engagement on stop  37  of sleeve  32 . In addition, a tongue  38  is arranged at the end of the second leg  35  and extends into a compression spring  39 . Compression spring  39  permanently acts upon the means  26  in the clockwise direction. Consequently, the leg  35  with an attachment  40  arranged on its rear side tends to move into abutment on the transverse member  11 . 
     Ventilation of the working chamber  3  is effected in the emergency braking position, when a predetermined relative displacement between valve piston  6  and control housing  8  is exceeded, whereby the reaction disc  9  is acted upon by the front part  14  and compressed elastically due to the effect of the control housing  8 . Simultaneously, a balance of forces develops at the pressure surface of the pressure member  27 , with the driver being completely released from reactions due to the clearance  28  between the front part of the valve piston and the pressure member  27 . Under the effect of the compression spring  39 , the leg  35  tends to perform a rotation in the clockwise direction and backgrips with its projection  36  the stop  37  of the sleeve  32  so that the sealing seat  15  is supported on the reaction disc  9  by way of the means  26  and the sleeve  32  as well as the pressure member  27 . The tilting movement of the means  26  is permitted because the transverse member  11  in the course of the actuating movement is released from the stop  20  on the housing, on the one hand, and has a clearance  42  within an indentation  41  close to the valve piston, on the other hand. In the panic braking position, the valve seat  15  is displaceable relative to the control housing  8  only in opposition to the actuating direction. Consequently, reduction of the slot at the sealing seat  16  is prevented. As can be described in the following, the brake force can be increased until the maximum brake effect without the driver feeling any reactions of the brake system. This means that the maximum boosting force of the booster can be produced even with a minimum input force, and the result is a transmission ratio which is increased compared to the normal braking function. 
     It can be taken from FIG. 4 that the output force of the b rake force booster may even be increased by the addition of pedal force, with the pressure member  27  entering the reaction disc  9  and the second sealing seat  16  being lifted to a major extent for a particularly quick ventilation of the working chamber  3 . In doing so, the base member  25  of the sealing seat  15  moves to abut on the front part  14  of the control housing under the effect of springs. Of course, this action is not free from reactions. 
     A basic aspect is the control of the brake force generated after a panic actuation because it is a major shortcoming of electrically operating panic braking aids (brake assist systems) of the art that these operate according to the on-off principle. More specifically, the boosting force of these prior art devices in the panic braking position is uncontrollable or controllable only with a maximum expenditure in electronics because the brake force booster directly reaches the range of maximum attainable boosting force and this condition can be interrupted only by complete release and related omission of the brake assist function. 
     FIG. 3 illustrates the action for reducing the boosting force generated in the emergency braking position. Starting from the position shown in FIG. 2, the valve piston  6  is retracted to the right by withdrawing the actuating pedal (not shown), and the clearance  28  close to the reaction disc is increased and, simultaneously, the slot at the second sealing seat  16  is closed. Because ventilation of the working chamber  3  does not occur, on the one hand, and there is a connection to the vacuum chamber  2  by way of the channels  19 ,  29 , on the other hand, evacuation of the working chamber  3  and, to the same extent, reduction of the boosting force will also occur. 
     It is likewise possible in the panic braking position to terminate the force reduction by depressing the brake pedal, with the result of displacement of the valve piston  6  to the left, whereby the first sealing seat  15  closes and the second sealing seat  16  opens so that a corresponding servo force develops. 
     Starting from the panic braking position, the device is moved into the ready position as follows. Because a low amount of brake force or no brake force is desired, the valve piston  6  is retracted until the transverse member  11  bears against the stop  20  on the housing. The sealing seats  15 ,  16  a re closed simultaneously so that evacuation of the first an d second chamber  2 ,  3  occurs. This causes a movement of the diaphram  4  together with the control housing  8  to the right, and the base member  25  is also urged to the right by abutment on an edge  43  provided at the front part  14  in opposition to the spring fores. At a defined point of time, the back side of the leg  35  with an attachment  40  abuts on the transverse member  11  and, with the return movement proceeding, there is a counterclockwise tilting movement of the means  26 , with the projection  36  being swivelled out of engagement relative to stop  37 . This consequently removes the panic braking position along with the related axial support of the first sealing seat  15 , and the brake force booster is available for the normal braking function or repeated panic braking functions. 
     According to a modified embodiment (not shown), it is also possible to terminate the panic braking function so that the pressure applied to the pedal is suddenly decreased only so far that the decrease will not cause a complete return movement of the control housing  8  in the above-described ready position but merely causes a limited withdrawal movement of the valve piston  6  relative to the control housing  8 . In this embodiment, the means  26  is configured so that it becomes ineffective during a predetermined relative displacement between the valve piston  6  and the control housing  8 , that means, it detaches the fixation in opposition to the actuating direction. This safeguards the movability of the valve seat  15  again so that the panic braking function is eliminated. 
     A modified embodiment is apparent from FIG. 5 which, in conformity with the preceding Figures, includes as a supporting means a tiltable and L-shaped lever  50  which is articulated at a base member  51  of a first sealing seat  53  that is principally axially movable in a control housing  52 . For an anti-friction guide that is locked against rotation, the base member  51  includes cylindrical pins by which it engages in corresponding bores of the control housing. The axial support of the sealing seat  53  is carried out indirectly on a reaction disc  54 . As an intermediate component, there is provision of a locking member  57  which bears against a front side  56  of the valve piston and is displaceable with it, rather than a sleeve slidable on the valve piston  55  as in the device described hereinabove. The locking member  57  adopts the same function as the sleeve and involves the advantage that it has larger dimensions (compared to the mentioned sleeve) so that the monitoring of dimensions and tolerance rating of very small dimensions is not necessary. Further, no friction appears (slip-stick effects). In FIG. 5, the lever  50  is shown in dotted lines in its (non-swivelled) normal braking position. The snapped-in or engaged panic braking position of the lever  50  is characterized in dash-dot lines. As becomes apparent also in connection with FIGS. 6,  7 , and  8 , the lever  50  has two, opposed pairs of legs  58 ,  58 ′,  59 ,  59 ′ offset in the shape of an L (roughly at right angles), which are interconnected at their leg ends by a yoke  60 ,  61 , respectively. Yoke  60  which interconnects the two first legs  58 ,  58 ′ serves for locking on the locking member  57  (in the panic braking position), and an elastically biassed spring element  62  abuts on the yoke  61  that interconnects the two second legs  59 ,  59 ′ in such a manner that the lever  50  permanently tends to perform a counterclockwise tilting movement about its bearing axis (in FIG.  5 ). Besides, this second yoke  61  is used for the release action, as will be described in the following. The tiltable support of the lever  50  is done by means of two aligning bearing eyes which engage in recesses in the base member  51  and this way form the bearing axis. According to the embodiment, the spring element  62  has a largely flat design and includes several resilient legs which are arranged in one piece on a transverse beam  63 . The legs are arranged on the transverse beam from radially inwards in an outward direction as follows. A first (centric) leg  64  is used to apply the mentioned counterclockwise biassing force to the lever  50 . Two second legs  65  extend through recesses in the control housing  52  and have each one deflected catch  66  for fixation in the control housing  52 . Two third legs  67  bear resiliently against a front side  68  of the base member  51  so that there is an elastic bias in opposition to the actuating direction also in this respect. It is an advantage in this respect that the flat spring element  62  not only requires extremely little space in an axial direction so that mounting space is economized. In addition, spring element  62  assumes a number of tasks and functions which usually must be fulfilled by other separate spring elements. For a well defined safe locking in the panic braking position, it is advisable that the locking member  57  be provided with a catch-type shoulder  69  or a catch-type step which the yoke  60  can backgrip in a sufficient relative displacement between the valve piston  55  and the base member  51  in such a fashion that displacement of the first valve seat  53  in the direction of the reaction disc  54  is no longer possible. More specifically, the valve piston position is fixed in relation to the respective sealing seats in the moment of locking such that decrease of the slot at the second sealing seat  70  is prevented. A one-time quick activation connected with a corresponding displacement of the valve piston  55  relative to the control housing  52  will thus lead to the full boosting force. This action is irrespective of whether the driver is pushed back to a certain degree by the reaction force (recedes in the course of braking), or without receding keeps his/her foot on the brake, with the pedal force being increased accordingly. 
     To remove the locking position, the operator withdraws the valve piston  55  (can be pushed back) until the working chamber is evacuated again by closure of the second valve seat  7  (control valve) and opening of the first valve seat  53 , and the control housing  52  follows the withdrawal movement of the valve piston  55 . When now the wedge  71  which is offset by 90° in FIG. 7 moves into abutment on a stop  72  on a housing shell  73 , and the base member  51  is also urged back under the spring effect of the third legs  67 , the second yoke  61  will come to abut on an end face of the wedge  71  fixed in position on the housing. The lever  50  will tilt back clockwise into the release position due to the fixed abutment of the yoke  61  on wedge  71  and the return movement of the control housing  52  along with the base member  51  in opposition to the actuating direction.