Abstract:
The invention relates to a pedal simulation device for simulating the reaction behaviour of a pedal, in particular of a brake pedal of a vehicle brake system, comprising a cylinder, a piston disposed displaceably inside the cylinder and coupled to the pedal and delimiting a working chamber inside the cylinder, a resetting element which, upon an actuation of the pedal, exerts a resetting force on the pedal, and a modelling device, which is fluidically connected to the working chamber, for influencing the reaction behaviour of the pedal. In the invention, for achieving the reaction behaviour it is provided that, upon an actuation of the pedal, by means of the modelling device a vacuum, which is arising or has arisen in the working chamber, is built up.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/151,142, filed Jun. 13, 2005 which is a continuation of International Application No. PCT/EP03/13583 filed Dec. 2, 2003, and which claimed priority to German Patent Application No. 102 60 008.2 filed Dec. 13, 2002, the disclosures of all of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a pedal simulation device for simulating the reaction behavior of a pedal, in particular of a brake pedal of a vehicle brake system, comprising a cylinder, a piston disposed displaceably inside the cylinder and coupled to the pedal and delimiting a working chamber inside the cylinder, a resetting element capable of exerting a resetting force on the pedal, and a modeling device, which is fluidically connected to the working chamber, for influencing the reaction behavior of the pedal. 
         [0003]    Such pedal simulation devices are already used in vehicles where an electrohydraulic brake system or an electromotive brake system is uncoupled from the brake force generation by means of a brake pedal. Such brake systems are referred to as “brake-by-wire” vehicle brake systems since the actual electrohydraulic or electromotive brake system that produces the braking effect is mechanically uncoupled from the brake pedal that initiates the braking operation. Rather, a brake pedal actuation is detected electronically by means of suitable sensors from various parameters, such as e.g., the actual brake pedal displacement or the force applied to the brake pedal as well as the brake pedal acceleration, and the respective brake system is controlled in accordance with the detected variables. In order nevertheless to convey to the driver of a motor vehicle a familiar mechanical brake pedal characteristic, whereby the brake pedal, upon actuation thereof, with increasing travel provides a growing resistance to further actuation and whereby the brake pedal in accordance with a hysteresis, upon release of the pedal, returns in a damped manner to its normal position, the pedal simulation devices of the initially described type are used. 
         [0004]    Such a pedal simulation device is known, for example, from DE 100 39 670 A1. With this pedal simulation device, upon actuation of the brake pedal, the piston connected thereto by a connecting rod is displaced in the cylinder. In the process, gas is pressed by means of a throttle device out of a working chamber that is enclosed by the cylinder and the piston. With the aid of the throttle device it is possible to influence the discharge behaviour of the gas and hence the resistance that arises during a movement of the piston inside the cylinder. It has however emerged that the pedal simulation device according to this background art has a relatively sluggish response characteristic. The reason for this is that, because of the high compressibility of the gas, the piston may move a relatively long way inside the cylinder without a sufficiently high resistance that is perceptible by the driver of the motor vehicle being offered to this movement on account of the compression of the gas and the effect of the throttle. It is only after the piston has been displaced by a considerable distance that the pressure increase inside the cylinder is sufficient to generate a perceptible resistance to the pedal actuation. The driver accordingly has the unwanted impression that the brake system only becomes active relatively late. 
         [0005]    From DE 197 55 481 C2 a pedal simulation device similar to the previously described background art is known. This device provides that, upon an actuation of the brake pedal, the gas enclosed between the piston and the cylinder may pass out of the working chamber in a substantially unimpeded manner through a non-return valve, wherein a resistance to the pedal movement is summoned up by means of a spring. During the resetting movement of the pedal, on the other hand, a throttle element, through which gas may pass in an inhibited manner into the working chamber enclosed by the piston and the cylinder, is effective so that a hysteresis is imposed on the movement of the brake pedal and the brake pedal may move under the action of the resetting spring in a damped manner into its normal position. However, the motional characteristic of this pedal simulation device differs widely from the desired behavior, especially because of the spring, which conveys to the driver a resistance to his pedal actuation that remains constant. 
         [0006]    From EP 0 771 705 B1, moreover, a brake pedal simulation device is known, in which the piston moves in a cylinder that is closed at both ends, so that the piston delimits a working chamber at each end. Provided in the piston is a bore that enables an ex-change of gas between the two chambers inside the cylinder. Upon actuation of the brake pedal, the piston moves inside the cylinder, wherein gas from the one working chamber may flow through the piston into the other working chamber. This leads however to inadequate damping of the piston movement, so that the resulting brake pedal characteristic differs widely from the one to be conveyed to the driver. 
         [0007]    Finally, from DE 196 38 102 C1 a vehicle hydraulic brake system is known, in which the basic idea of uncoupling of the brake pedal from the actual brake system is realized. 
       BRIEF SUMMARY 
       [0008]    An object of the present invention is to provide a pedal simulation device of the initially described type, which, while being of a simple construction and operationally reliable, responds rapidly and has an improved pedal characteristic compared to the background art. 
         [0009]    This object is achieved by a pedal simulation device for simulating the reaction behavior of a pedal, in particular of a brake pedal of a vehicle brake system, comprising a cylinder, a piston disposed displaceably inside the cylinder and coupled to the pedal and delimiting a working chamber inside the cylinder, a resetting element capable of exerting a resetting force on the pedal, and a modeling device, which is fluidically connected to the working chamber, for influencing the reaction behavior of the pedal. With this pedal simulation device, according to the invention it is provided that, upon an actuation of the pedal, a vacuum builds up in the working chamber. 
         [0010]    The vacuum that builds up in the working chamber upon actuation of the brake pedal is dependent on the behavior of the modeling device and is reducible by means of a fluid flowing through the modeling device. Because of the preferably relatively small (dead) volume of the working chamber at the start of actuation of the pedal, this vacuum may assume a relatively large value within a relatively short time of the pedal actuation, i.e. after a relatively short actuating distance, so that the pedal simulation device responds rapidly. The modeling device then allows only a limited replenishing flow of fluid into the working chamber, with the result that the pedal is actuable only with appropriate resistance. Upon release of the pedal, the pedal is returned to its normal position by the resetting element, which may be of any desired configuration, wherein this resetting movement is likewise influenceable by the modeling device. 
         [0011]    As a fluid, according to the invention suitable liquids, such as e.g. brake fluid or glycerol, may be used. The invention is however particularly suitable for use also in a pneumatic system, so that as a fluid it is possible to use a gas or gas mixture, in particular air, the compressibility and expansibility of which is utilized. In the following, therefore, the invention is discussed in particular with regard to the use of a gaseous fluid. 
         [0012]    According to the invention, it may be provided that the modeling device connects the working chamber to the ambient atmosphere. Alternatively, it may also be provided that the modeling device connects the working chamber to a fluid reservoir that is separated or separable from the ambient atmosphere. It is advantageous for the fluid, upon actuation of the pedal, to flow from outside of the cylinder into the working chamber. 
         [0013]    In order to achieve the damping effect of the modeling device, according to the invention it may be provided that the modeling device comprises at least one throttle channel having a throttle device. This throttle device may be a pre-configured throttle device. On the other hand, in a development of the invention it is provided that the throttle device is adjustable. The throttle device may be adjusted manually during the original assembly and during maintenance of the brake system. It is however also equally possible for the throttle device to be actively controlled and adjusted during operation of the vehicle brake system, e.g. in such a way that in dependence upon various operating states of the brake system or driving situations the throttle device may assume different states and therefore convey to the driver different braking characteristics that also differ in each case in dependence upon the operation of the vehicle brake system. 
         [0014]    Furthermore, in a development of the invention the modeling device may comprise a bypass channel that bypasses the throttle channel. It is therefore possible that, upon a release of the pedal after actuation thereof, under the action of the resetting element fluid flows out of the working chamber through the bypass channel. This means that an actuation of the pedal is counteracted by an appropriately high resistance owing to the throttle device but that, upon release of the pedal after prior actuation, the throttle device may be substantially bypassed so that the resetting movement may be effected with markedly weakened damping and hence ultimately faster. A hysteresis is therefore imposed on the pedal movement. This may be achieved, for example, in that the by-pass channel has a non-return valve that allows fluid to pass substantially unimpeded out of the working chamber and prevents fluid from passing into the working chamber. The use of a non-return valve has the advantage that it is a relatively simple and hence inexpensively available, operationally reliable component. 
         [0015]    In a development of the pedal simulation device according to the invention, it is provided that the cylinder is closed at its end remote from the working chamber and together with the piston encloses a complementary working chamber and that, upon an actuation of the brake pedal, fluid from the complementary working chamber flows out of the cylinder through the modeling device. This measure provides that in addition to the working chamber a further working chamber, namely the complementary working chamber, is provided, by means of which the behavior of the brake pedal may be further influenced. The modeling device accordingly comprises components, which are associated with the working chamber, and further components, which are associated with the complementary working chamber. 
         [0016]    When in this connection there is mention of a modeling device, this term is not necessarily intended to mean that all of the components provided for influencing the reaction behavior of the pedal are combined in a common assembly group. Rather, the term modeling device is intended to be a generic term for the components that may influence the reaction behavior of the pedal, irrespective of whether they are combined in a common assembly group or associated in each case separately with the working chamber or the complementary working chamber. 
         [0017]    It may also be provided with regard to the complementary working chamber that this chamber is connected by the modeling device to the ambient atmosphere, or that this chamber is alternatively connected by the modeling device to a fluid reservoir that is separated or separable from the ambient atmosphere. 
         [0018]    Furthermore, in an analogous manner to the components of the modeling device that are associated with the working chamber it may be provided that the modeling device also comprises at least one throttle channel associated with the complementary working chamber and having a throttle device, wherein this throttle device associated with the complementary working chamber may also be sporadically or permanently controllable and hence adjustable. Equally, the modeling device may also comprise a bypass channel, which is associated with the complementary working chamber and by means of which the throttle device associated with the complementary working chamber may be bypassed. 
         [0019]    It should however be pointed out that the components associated with the complementary working chamber, namely the throttle device and bypass channel, may be disposed the opposite way round to the components of the working chamber according to the previous description. In other words, this means that, upon a release of the pedal after actuation thereof, under the action of the resetting element fluid flows into the complementary working chamber through the bypass channel. If, for example, as already explained above with regard to the working chamber—the actuation of the brake pedal is to be effected in a damped manner and the resetting movement is to occur only with slight damping, then in the context of this development of the invention it is provided that, upon actuation of the brake pedal, the fluid displaced from the complementary working chamber has to flow through the throttle device associated with the complementary working chamber and, in so doing, closes the non-return valve. Upon a sub-sequent release of the pedal, fluid then has to flow from the ambient atmosphere into the complementary working chamber. This occurs substantially through the non-return valve, which opens in this flow direction, so that only a small proportion of the fluid flowing into the complementary working chamber flows through the throttle device. 
         [0020]    In a development of the invention it may further be provided that the working chamber and the complementary working chamber are connected by the modeling device, wherein, upon an actuation of the pedal, fluid from the complementary working chamber flows through the modeling device into the working chamber and wherein, upon a release of the pedal after actuation thereof, fluid from the working chamber flows through the modeling device into the complementary working chamber. In this variant of the invention, the modeling device may comprise a throttle device as well as a by-pass channel with non-return valve, wherein the non-return valve is oriented in such a way that, given a flow from the complementary working chamber into the working chamber, it blocks and, given a flow in the opposite direction, it opens. Consequently, upon an actuation of the pedal, the fluid is sucked out of the complementary working chamber, through the throttle device and into the working chamber, without any possibility of a fluid flow occurring through the bypass channel. After release of the pedal, the pedal and hence the piston in the cylinder are pushed back to their normal position under the action of the resetting element, wherein the fluid situated in the working chamber may flow through the bypass channel with the open non-return valve in a substantially unimpeded manner back into the complementary working chamber. 
         [0021]    Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the various embodiments, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a diagrammatic overview representation of a pedal designed as a brake pedal. 
           [0023]      FIG. 2  is a detail view of the pedal simulation device according to a first embodiment of the present invention. 
           [0024]      FIG. 3  is a detail view as in  FIG. 2  according to a second embodiment of the present invention. 
           [0025]      FIG. 4  is a detail view as in  FIGS. 2 and 3  according to a third embodiment of the present invention. 
           [0026]      FIG. 5  is a detail view as in  FIGS. 2 to 4  according to a fourth embodiment of the present invention. 
           [0027]      FIG. 6  is a force/displacement diagram for a more detailed explanation of the pedal simulation device according to the invention and the background art. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows diagrammatically how a pedal simulation device  10  according to the invention, which in this described case is designed as a brake pedal simulation device, interacts with a brake pedal  12 . The brake pedal  12  is attached in a rotatable manner to a suspension device  14  on a vehicle body  16  and coupled by a swivel joint  18  to an actuating rod  20  for joint movement. At its end remote from the suspension device  14 , the brake pedal  12  has a bearing pad  22 , on which a driver of a vehicle, in order to actuate the vehicle brake, exerts the brake actuating force F B  by depressing the pad  22  with his foot. On completion of the braking operation, the driver reduces the brake actuating force F B  and releases the brake pedal  12 . 
         [0029]    The actuating rod  20  runs into the diagrammatically illustrated pedal simulation device  10 , which is described in detail below. On the actuating rod  20 , a stop  24  is provided in a fixed manner. Supported against this stop is one end of a resilient resetting element in the form of a spring  26 . The other end of the spring  26  is supported against the side of the housing of the pedal simulation device  10  facing the brake pedal  12 . The spring  26 , upon actuation of the brake pedal  12  and the thereby initiated sliding of the actuating rod  20  into the housing of the pedal simulation device  10 , is compressed and, upon subsequent release of the brake pedal  12 , gives rise to a resetting movement. 
         [0030]    The pedal simulation device  10  comprises sensors (not shown in detail), by means of which parameters characterizing the actuation of the brake pedal  12 , such as e.g. the actuating speed, the actuating distance or the magnitude of the pedal actuating force F B , are detected and transmitted via the lines  28 ,  30 ,  32  to a control unit. The control unit then, in accordance with the detected parameters, subsequently controls the vehicle brake system, e.g. a hydraulic or electromechanical vehicle brake system (not shown in either case). 
         [0031]    There now follows a detailed description of the construction and mode of operation of the pedal simulation device  10 . For this purpose, reference is made to  FIGS. 2 to 5 , which show individual embodiments of the pedal simulation device  10 . 
         [0032]    The first embodiment shown in  FIG. 2  shows a pedal simulation device  110  comprising a cylinder  134 , which is open at one end and has a working piston  136  guided therein. The working piston  136  is coupled to the actuating rod  120  for joint movement. The actuating rod  120  extends through an axial opening  138 , wherein in the axial opening a sealing ring  140  is disposed. The effect achieved by the sealing ring  140  is that the actuating rod  120  may be moved axially back and forth in a fluid-tight manner inside the axial opening  138 , as is represented in  FIG. 2  by arrow P. 
         [0033]    A sealing ring  142  is provided also at the peripheral surface of the working piston  136  facing the inner wall of the cylinder  134 , so that the working piston  136  may also be moved back and forth in a fluid-tight manner inside the cylinder  134  together with the actuating rod  120 . 
         [0034]    The cylinder  134  together with the working piston  136  and the actuating rod  120  therefore enclose an annular working chamber  144 . A radial opening  146  is introduced close to the sealed end of the cylinder  134  into the side wall thereof. The radial opening  146  communicates with a fluid line  148 , with which a throttle device  150  is associated. The throttle device  150  is manually or electromechanically adjustable, thereby allowing a variation of the flow cross section of the fluid line  148  within a preset scope. 
         [0035]    The working chamber  144  is filled with air and, upon opening of the fluid line  148  and/or the throttle device  150 , communicates with the ambient atmosphere. 
         [0036]    If the brake pedal  12  according to  FIG. 1  is then actuated by the brake actuating force F B , the actuating rod  120  is then displaced in accordance with arrow P 1  in  FIG. 2  to the right. This leads to the piston  136  together with the actuating rod  120  moving inside the cylinder  134  in  FIG. 2  to the right. The volume of the working chamber  144  is therefore increased, so that a vacuum arises therein. The effect of this vacuum is that the working chamber  144  takes in air from the ambient atmosphere through the radial opening  146 , the fluid line  148  and the throttle device  150 . The throttle device  150  however inhibits this intake of ambient air so that ultimately, by virtue of the vacuum arising in the working chamber  144 , the movement of the actuating rod  120  and hence of the brake pedal  12  may occur only subject to resistance. In addition to the resistance generated by the spring  26  upon compression thereof, the driver perceives a resistance that originates from the development of the vacuum in the working chamber  144 . In dependence upon the actuation of the brake pedal  12 , i.e. in dependence upon the value of the applied brake actuating force F B , the speed of actuation and the actuating distance of the brake pedal  12  as well as in dependence upon the throttle position of the throttle device  150 , an amount of resistance arises in each case. It is therefore possible by means of the pedal simulation device  110  to convey to the driver a resistance characteristic for the actuation of the brake pedal  12  that allows the driver to believe that the brake pedal  12  is interacting directly with the brake system of the vehicle. In reality, however, the interaction occurs merely via sensors, which are not shown in  FIGS. 1 and 2  and which—in accordance with, as such, known brake-by-wire brake systems—transmit parameters characterizing the actuation of the brake pedal  12  via the lines  28 ,  30  and  32  to a control unit, so that the brake system is then controlled electronically in accordance with the parameters. 
         [0037]    Upon a release of the brake pedal  12  after actuation, i.e. upon a reduction of the brake actuating force F B —in an extreme case to zero, the actuating rod  120  does not shoot suddenly from its deflected position into the normal position shown in  FIG. 1 . Rather, the resetting movement initiated by the spring  26  is also effected in a damped manner, because then the air situated in the working chamber  144  and pressed out of there by the action of the spring  26  has to be discharged into the ambient atmosphere again through the throttle device  150 . In said case, the throttle device  150  in turn acts as a damping element, with the result that the resetting movement is effected in a retarded manner. 
         [0038]    With the embodiment according to  FIG. 2  it is possible, upon an actuation of the brake pedal  12 , to achieve a sufficiently fast response of the pedal simulation device  110  because the vacuum arising in the working chamber  144  increases relatively quickly and the throttle device  150  leads to a rapidly growing resistance to the axial movement of the working piston  136 . This may be gathered also from  FIG. 6 , which shows a diagram representing the resistance force F working piston  arising at the working piston  136  over the displacement distance S working piston  of the working piston  136 . 
         [0039]    If in  FIG. 6  one examines, for example, the curve  152 , which characterizes the embodiment according to  FIG. 2  for a specific setting of the throttle device  150 , then it is evident that, in order to achieve a specific resistance force F 1 , a movement of the working piston by the distance S 1  is required. Up to attainment of this resistance force F 1  at the working piston  136 , the resistance force rises relatively steeply in accordance with the curve  152 . As the volume of the working chamber  144  increases, however, this rise levels out until it finally takes an asymptotic course. The curve  152  corresponds to the situation where at the start of an actuation of the brake pedal  12  there is a slight dead volume in the chamber  144  (S working piston ≈0). In the case of a larger dead volume at the start of an actuation of the brake pedal, the characteristic indicated by the curve  154  is obtained. The curve  154  shows an initially flatter rise. 
         [0040]      FIG. 6  further shows two dashed curves representing the course of the resistance force at the working piston in systems according to the initially described background art according to DE 100 39 670 A1. In these systems, as already explained initially, the resistance force is generated, not by means of a vacuum, but by means of an above-atmospheric pressure generated in the cylinder by means of the displaced working piston. Thus, the curve  156  initially, i.e. given a small actuating distance, shows a markedly flatter rise than the curve  152 , with the result that the working piston has to travel a much greater distance S 2  before the desired resistance force F 1  is attained at the working piston. Then, however, there is a much stronger rise in the resistance generated by the pedal simulation device. The curve  158  corresponds to the damping in the situation of return travel of the brake pedal. The area between the two curves  156  and  158  therefore corresponds to the hysteresis of a brake pedal actuating cycle. 
         [0041]    The characteristic curves illustrated in  FIG. 6  apply to the situation of constant actuating speed of the brake pedal  12 . Given faster actuation, a greater resistance is offered to the actuation, and conversely. Such an actuating behavior is desirable because it corresponds to the usual actuating behavior of conventional brake systems with a vacuum brake booster. The reason for the actuating-speed-dependent characteristic course in the embodiment according to  FIG. 2  is the fact that at a lower actuating speed a lower vacuum arises in the working chamber  144  than at a high actuating speed. The reason for this is the flow characteristic of the throttle device  150 . 
         [0042]    In summary, it may be stated with regard to  FIG. 6  that the pedal simulation device according to the invention, which operates with a vacuum, responds more rapidly to an actuation of the brake pedal  12  than the pedal simulation devices according to the background art, which operate with above-atmospheric pressure. 
         [0043]    There now follows a description of the second embodiment of the pedal simulation de-vice according to the invention, which is illustrated in  FIG. 3 . To simplify the description and avoid repetition, the same reference characters are used as with regard to  FIGS. 1 and 2 , only with the number “2” placed in front. Only the differences from the first embodiment according to  FIG. 2  are described. 
         [0044]    The second embodiment according to  FIG. 3  differs from the first embodiment according to  FIG. 2  only in that the fluid line  248 , which is coupled to the radial opening  246 , comprises a bypass line  260  that bypasses the throttle device  250 . Provided in the bypass line  260  is a non-return valve  262 , which prevents air from the ambient atmosphere from flowing into the radial opening  246  and hence into the working chamber  244 . A flow of air in the opposite direction, i.e. a flow of air from the working chamber  244  through the radial opening  246  towards the ambient atmosphere may however pass substantially unimpeded through the non-return valve  262 . 
         [0045]    In operation, the pedal simulation device  210  according to  FIG. 3  therefore behaves differently to the pedal simulation device  110  according to  FIG. 2  in that, upon a resetting movement of the actuating rod  220  and hence of the working piston  236  in accordance with arrow P 2 , the air contained in the working chamber  244  may pass substantially unimpeded into the ambient atmosphere, wherein the throttle device  250  is bypassed by means of the bypass line  260 . This means that the brake pedal  12  may move under the action of the spring  26  and substantially without damping by the throttle device  250  relatively quickly into its normal position. On the other hand, the throttle device  250  in the second embodiment according to  FIG. 3  acts in the same way as the embodiment according to  FIG. 2  because, when air from the ambient atmosphere is taken into the working chamber  244 , the non-return valve  262  closes and prevents a flow of air through the bypass line  260 . 
         [0046]      FIG. 4  shows a third embodiment of the pedal simulation device  310  according to the invention. The same reference characters are used for the identical or equivalent components as with regard to  FIGS. 1 to 3 , only with the number “3” placed in front. 
         [0047]    The third embodiment according to  FIG. 4  differs from the second embodiment according to  FIG. 3  in that the cylinder  334  is no longer open at one end but is closed at its end remote from the actuating rod  320  by the end wall  364 . In the cylinder  334  there is therefore, in addition to the working chamber  344 , a complementary working chamber  366  that is delimited at one end by the working piston  336 . Opening into this complementary working chamber  366  close to the end wall  364  is a further radial opening  368 . The radial opening  368  communicates with a fluid line  370 , which comprises, on the one hand, a throttle channel with an adjustable throttle device  372  and, on the other hand, a bypass channel  374  with a non-return valve  376 . The non-return valve  376  is disposed in such a way that it allows air from the ambient atmosphere to flow unimpeded through the bypass line  374 , via the radial opening  368  and into the complementary working chamber  366  but prevents air from flowing out of the complementary working chamber  366  through the radial opening  368 . The effect of this is that, upon a movement of the actuating rod  320  and the working piston  336  in the direction of arrow P 1 , the air contained in the complementary working chamber  366  has to flow through the throttle device  372  and so the outward flow is damped by means of the throttle device  372 . Upon a movement of the actuating rod  320  and the working piston  336  in accordance with arrow P 2 , on the other hand, air from the ambient atmosphere may pass substantially unimpeded through the non-return valve  376 , via the radial opening  368  and into the complementary working chamber  366 , so that this movement is substantially not damped and/or inhibited by the throttle device  372 . 
         [0048]    Compared to the pedal simulation devices according to  FIGS. 2 and 3 , the pedal simulation device according to  FIG. 4  presents a reaction behavior upon the brake pedal  12  that differs in that, with increasing displacement distance of the working piston  336  inside the cylinder  334 , the pressure inside the complementary working chamber  366  rises more and more. The effect of this is that, when the rise of the vacuum in the working chamber  344  levels off with increasing displacement distance of the working piston  336 , as explained with regard to curve  152  in  FIG. 6 , the effect of the complementary working chamber  366 , in which an above-atmospheric pressure builds up, is utilized. As a result, the resistance force reacting upon the brake pedal  12  increases perceptibly for the driver even with increasing displacement movement of the working piston  336 . 
         [0049]    In other words, the pedal simulation device  310  according to  FIG. 4  presents a relatively fast response, wherein even in the event of extreme and/or sustained actuation of the brake pedal with sufficiently high brake actuating force F B  and correspondingly high brake pedal displacement the resistance reacting upon the brake pedal continues to increase perceptibly. 
         [0050]    Finally,  FIG. 5  shows a fourth embodiment of the pedal simulation device  410  according to the invention. For the description of this embodiment, the previously used reference characters are used once more for components of an identical type or an identical effect, only with the number “4” placed in front. 
         [0051]    The fourth embodiment according to  FIG. 5  differs from the third embodiment according to  FIG. 4  only in that the two fluid lines  448  and  470  are connected to one another, wherein these fluid lines have a common throttle device  450  and a common bypass channel  460  having the non-return valve  462  for bypassing the throttle device  450 . The effect of this construction is that upon a movement of the actuating rod  420  and the working piston  436  in accordance with arrow P 1 —without an exchange of air with the ambient atmosphere—air from the complementary working chamber  466  is sucked through the radial opening  468 , the throttle device  450  and the radial opening  446  into the working chamber  444 . This occurs in a throttled manner, wherein the non-return valve  462  closes so that no air flow may occur through the bypass channel  460 . Such a movement of the actuating rod  420  in accordance with arrow P 1  is therefore damped. Upon a movement in the opposite direction in accordance with arrow P 2 , on the other hand, air from the working chamber  444  is pressed through the radial opening  446  into the fluid line  448 . Given this flow direction of the air, the non-return valve  462  opens so that the air, while substantially bypassing the throttle device  450 , flows into the fluid line  470  and the radial opening  468  and through the latter into the complementary working chamber  466 . The pedal simulation device  410  according to the fourth embodiment according to  FIG. 5  therefore presents a similar reaction behavior upon the brake pedal  12  to the pedal simulation device  210  according to  FIG. 3 . One advantage of the fourth embodiment according to the invention according to  FIG. 5  is that it is a closed pneumatic system that is not exposed to pollution by incoming ambient air. 
         [0052]    It should be pointed out that the embodiments described above with reference to  FIGS. 2 to 6  may be combined with one another in any desired manner to produce different characteristic curves of the reaction behavior. 
         [0053]    It was explained above that the invention may be used to provide pedal simulation devices of differing design, which react relatively fast to an actuation of the brake pedal. It should be pointed out that the adjustable throttle devices used may be adjustable manually during assembly and during maintenance. It is also equally possible for these throttle devices during operation of the brake system to be permanently, e.g. electro-mechanically controllable in order to vary their throttling behavior and hence the behavior of the pedal simulation device. It is therefore possible, for example, to switch between a sporty setting, in which the pedal has a relatively rapid, strong response, and a moderate setting, in which the pedal has a slightly retarded and relatively gentle response. It should moreover be pointed out that, as already indicated several times above, the throttle devices according to the present invention are used primarily to damp the piston movement upon an actuation of the brake pedal but that, as was also explained with reference to  FIG. 2 , during a return travel movement of the working piston, i.e. during a resetting movement, these throttle devices may equally demonstrate a throttling action and may therefore also damp this movement. 
         [0054]    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.