Abstract:
A pneumatic vehicle brake system includes first and second groups of wheel brakes belonging, respectively, to first and second brake circuits having first and second compressed air storage tanks for providing first and second stored pressures. At least one first circuit brake cylinder is a combined spring-store/diaphragm cylinder with a spring store part for providing a parking brake and a diaphragm part for providing a service brake. If the first circuit fails, the spring store part is deaerated to engage the parking brake. A pressure sensor for measuring the first stored pressure is connected to a control unit that controls a modulator for aerating and deaerating the spring store part. The control unit generates a signal for an electrically actuatable modulator solenoid valve if the value measured by the sensor falls below a minimum value, such that the spring store part can be aerated and deaerated via the valve.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to an electropneumatic vehicle brake control system and method for controlling a parking brake. 
     BACKGROUND OF THE INVENTION 
     A known brake system of the general type under consideration is shown in  FIG. 1 . Referring to  FIG. 1 , brake system  10  is part of a vehicle having four wheels  12 , each of which is provided with a wheel-speed sensor  14 , which, via respective electrical lines  18 , is electrically connected to a control unit  16 . The wheel brakes are provided with respective brake cylinders  20 ,  22 , wherein brake cylinders  22  of the rear axle are designed as combination spring-actuated/diaphragm cylinders. They therefore have a spring-actuator part and a diaphragm part. The spring-actuator part is a parking brake component. The diaphragm part is a service brake component. 
     The service brake and the parking brake are pneumatically actuated. Braking intent of the vehicle operator is converted by means of a brake actuating device  22  into a modulated brake pressure. This modulated brake pressure is supplied via compressed air lines  24 ,  26  and  28  to solenoid valves  30  of an anti-lock braking system and via further compressed air lines  32  to brake-cylinders  20  of the front axle. Analogously, the modulated brake pressure is supplied via compressed air lines  34 ,  36 ,  38 , via a relay valve  40 , further via compressed air lines  42  to solenoid valves  44  of the anti-lock braking system and further via compressed air lines  46  to combination spring-actuated/diaphragm cylinders  22  of the rear axle. 
     Compressed air lines  34 ,  36 ,  38 ,  42  and  46  to combination spring-actuated/diaphragm cylinders  22  of the rear axle form, together with further components, such as solenoid valves  44 , relay valve  40  and a compressed air reservoir tank  48 , a first brake circuit, referred to as brake circuit I, wherein compressed air reservoir tank  48  is pneumatically in communication via further compressed air lines  50  with brake actuating device  22  as well as relay valve  40 . Analogously, compressed air lines  24 ,  26 ,  28 ,  32  as well as solenoid valves  30  form, together with brake cylinders  20 , a second brake circuit, referred to as brake circuit II, wherein brake actuating device  22  is in communication via further compressed air lines  52  with a second compressed air reservoir tank  54 . Both compressed air reservoir tanks  48 ,  54  are supplied with compressed air by a compressor. 
     The parking brake can be actuated by means of a pneumatic switch  56 . The spring-actuator part of combination spring-actuated/diaphragm cylinders  22  can be vented by means of switch  56 , whereby the parking brake is engaged. The parking brake is released by admission of air to the spring-actuator part. For this purpose, via compressed air lines  58 ,  60 ,  62 , compressed air can be supplied to combination spring-actuated/diaphragm cylinders  22  and discharged therefrom. Also, for this purpose, compressed air control is exercised, on the one hand, via switch  56  and, on the other hand, via an inverting relay valve  64  as well as a valve  66 . 
     At the same time, inverting relay valve  64  performs a further function. For this purpose it is in communication with the modulated pressure of front-axle brake circuit II via compressed air line  24  and a compressed air line  68 , as well as with the modulated pressure of rear axle brake circuit I via compressed air line  34  and a compressed air line  70 . 
     In the event of failure of the first brake circuit, that is, if service braking by means of brake circuit I is no longer possible, inverting relay valve  64  is tasked with activating the parking brake, or, in other words, the spring-actuator part of combination spring-actuated/diaphragm cylinders  22 . Even in the event of failure of rear axle brake circuit I, therefore, the rear axle can be braked sufficiently by means of the spring actuators to achieve the necessary braking distance. 
     In the event of failure or drop of pressure in rear axle brake circuit I, a high modulated pressure of front-axle brake circuit II and a low or zero pressure of rear axle brake circuit I is present at inverting relay valve  64 . For this purpose, the inverting relay valve is designed such that, in the event of such a pressure difference between the modulated pressures of the two brake circuits I and II, it lowers the output pressure at inverting relay valve  64 , or, in other words, the pressure in compressed air line  60 . Thereby, the spring actuators of brake cylinders  22  of the rear axle are vented, so that the parking brake is able to assist or take over the function of the service brake. Even in the event of failure of the rear axle brake circuit, therefore, a specified braking distance can be achieved. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to simplify such known brake systems. In accordance with embodiments of the present invention, a pneumatic brake system for a vehicle includes pneumatically actuatable brake cylinders for actuation of wheel brakes. Together with other components, such as compressed air lines, valves and a first compressed air reservoir tank for supplying a first reservoir pressure, a first group of wheel brakes forms a first brake circuit. Together with other components, such as compressed air lines, valves and a second compressed air reservoir tank for supplying a second reservoir pressure, a second group of wheel brakes forms a second brake circuit. At least one brake cylinder of the first brake circuit is designed as a combination spring-actuated/diaphragm cylinder with a spring-actuator part for supplying a parking brake and a diaphragm part for supplying the service brake. In the event of failure of the first brake circuit, the spring-actuator part can be vented in order to engage the parking brake. According to embodiments of the present invention, a pressure sensor for measuring the first reservoir pressure is provided for this purpose and is connected to an electronic control unit. This electronic control unit controls a modulator for modulation of the compressed air to the spring-actuator part, so that admission of air to and venting of the spring-actuator part can be achieved. The control unit generates an electrical control signal for an electrically actuatable solenoid valve of the modulator, by means of which the supply or discharge of compressed air to or from the spring-actuator part can be controlled indirectly, or, in other words, by involvement of further devices, such as an air-flow-boosting valve device, or directly. This control signal is generated when the value measured by the first pressure sensor has dropped below a predetermined minimum pressure value. In this case, the control logic recognizes that the first brake circuit has failed. The control logic then drives the solenoid valve of the modulator such that the spring-actuator part of the spring-actuated/diaphragm cylinder is vented, thus ensuring that the parking brake is engaged continuously or temporarily. 
     By means of the pressure sensor and of the design of the control unit, the conventional inverting relay valve can be omitted. The brake system can therefore be designed without this component. In this way, the brake system has a simpler and less costly construction. 
     According to another embodiment of the present invention, a second pressure sensor for measuring the pressure of the second brake circuit modulated by means of a brake actuating device is provided and connected to the electronic control unit, wherein the control signal for the solenoid valve can be generated as a function of the value measured by the second pressure sensor. By virtue of the measurement of the modulated pressure of the second brake circuit and the generation of the control signal as a function of this measured modulated pressure value, the brake force exerted by the spring-actuator part can be made to depend on actuation of the brake actuating device by the vehicle operator. Even in the event of failure of the first brake circuit, therefore, braking of the wheels belonging to this brake circuit is achieved by means of the parking brake and, indeed, in a manner that can be metered by the vehicle operator, since the corresponding brake pressure is modulated as a function of the operator&#39;s intent. 
     According to a further embodiment of the present invention, the control signal for the solenoid valve can be generated as a function of a signal representing the braking intent of the vehicle operator. For this purpose, the braking intent of the vehicle operator is recorded and converted into a signal. This signal can be obtained in various ways. Advantageously, therefore, the signal representing the vehicle operator&#39;s intent is an electrical analog or digital signal generated by an electronic brake system. As an example, such signals are specified as digital messages, especially the SAE message “brake pedal position”, with a range of values from 0 to 100, for example. Such a message is processed by the electronic control unit, which then generates the control signal for the solenoid valve for admitting air to and venting of the spring actuator. 
     Advantageously, the control signal for this solenoid valve is generated as a function of a brake actuating signal, which is supplied by means of a displacement sensor disposed on the brake pedal. In this way, the position of the brake pedal is sensed and, thus, associated with the braking intent of the vehicle operator. The signal generated by this sensor is processed, in turn, in the electronic control unit, in order to supply the control signal for the solenoid valve. 
     According to another embodiment of the present invention, the control signal for the solenoid valve is generated as a function of an electrical signal, which is passed to an electrically controllable valve for control of the pressure in the second brake circuit. As an example, this valve can be a proportional relay valve, which is opened or closed by means of an electrical signal in order to activate the pressure in the second brake circuit. This electrical signal, in turn, also represents the braking intent of the vehicle operator. Therefore, this signal can also be used by the electronic control unit in order to supply the control signal for the solenoid valve. 
     According to yet another embodiment of the present invention, a third pressure sensor is provided for measuring pressure supplied by the modulator to the spring-actuator part, the third pressure sensor also being connected to the electronic control unit. After the measurement of the pressure value, the measured pressure value is compared with the modulated pressure of the second brake circuit measured by means of the second pressure sensor, or the two measured pressure values are mutually offset and the control signal is regulated as a function of the result obtained thereby. In this way, the brake force exerted by means of the parking brake on the wheel brakes associated with the first brake circuit can be adapted to the brake force of the wheel brakes associated with the second brake circuit. This brake force of the first brake circuit can, in principle, be adjusted to be higher or lower than or exactly equal to the brake force of the second circuit. This adjustment is guided by the vehicle structure and, possibly, by its load condition. 
     According to yet a further embodiment of the present invention, the control unit is connected to wheel-speed sensors and/or to a controller of an anti-lock braking system, in order that locking of the wheels of the first brake circuit can be detected in this way. For this purpose, the speeds of the wheels of the first brake circuit are measured. If a sudden decrease of the wheel speed or immobilization of the wheels of the first brake circuit occurs, locking of the wheels or of one of the wheels is detected. In this case, the speed of the wheel does not correspond to the vehicle speed. In the event of locking, air is admitted to the spring-actuator part, because the control unit changes the control signal to the solenoid valve in a way that ensures admission of air to the spring-actuator part. As a result, the parking brake is released. If it is found thereafter in a new measurement of the speeds of the wheels of the first brake circuit that the wheel speeds correspond to the vehicle speed, the spring-actuator part can be vented again and, thus, the parking brake can be engaged again. In this way, anti-lock protection can be achieved even in the case of braking by means of the spring actuators. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, arrangement of parts, and the various steps and the relation of one or more of such steps with respect to each of the others, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  depicts a conventional (prior art) brake system; 
         FIG. 2  depicts an exemplary embodiment of an inventive brake system; and 
         FIG. 3  is a schematic view of part of the brake system depicted in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  shows, for a vehicle having a plurality of wheels, namely four wheels  74  in the illustrated example, each wheel being provided with a wheel-speed sensor  76 , which is connected electrically via a respective electrical line  78  to an electronic control unit  80 , an inventive brake system  72 , which can be implemented in vehicles such as, for example, commercial vehicles, heavy motor trucks, buses, etc. Wheels  74  are provided with respective wheel brakes having brake cylinders  82 ,  84 , wherein brake cylinders  84  are associated with a rear axle and are designed as combination spring-actuated/diaphragm cylinders. Brake cylinders  84  are, therefore, each provided with a spring-actuator part  86  and a diaphragm part  88 , as shown in  FIG. 3 . Spring-actuator part,  86  is a component of the parking brake, whereas diaphragm part  88  is a component of the service brake. 
     According to an exemplary embodiment of the present invention, both the service brake and the parking brake are pneumatically actuated or released. Braking intent of the vehicle operator is converted by means of a brake pedal of a brake actuating device  90  into a modulated brake pressure. The modulated brake pressure is supplied via compressed air lines  92 ,  94 ,  96 , preferably, via relay valve  98 , solenoid valves  100  of an anti-lock braking system and via further compressed air lines  102 , to brake cylinders  82  of a front axle of the vehicle. Analogously, the modulated brake pressure for the rear axle is passed from brake actuating device  90  via further compressed air lines  104 ,  106 , via an air-flow-boosting valve device or a relay valve  108 , further via compressed air lines  110  to solenoid valves  112  of the anti-lock braking system and then further via compressed air lines  114  to combination spring-actuated/diaphragm cylinders  84 . 
     Compressed air lines  104 ,  106 ,  110 ,  114  as well as air-flow-boosting valve device  108  and solenoid valves  112 , together with further components, especially a compressed air reservoir tank  116  and compressed air lines  118 ,  120  and  122  from compressed air reservoir tank  116  to brake actuating device  90 , form a first brake circuit, referred to as brake circuit I or rear axle brake circuit. Analogously, compressed air lines  92 ,  94 ,  96 ,  102  as well as relay valve  98 , if applicable, and solenoid valves  100  form a second brake circuit, referred to as brake circuit II or front-axle brake circuit, wherein brake actuating device  90  is in communication via further compressed air lines  124 ,  126 ,  128  with a second compressed air reservoir tank  130 . Both compressed air reservoir tanks  116 ,  130  are supplied with compressed air by a compressor or a common compressed air reservoir  132 . 
     A parking brake is formed by the following components among others: an electrical actuating device  134 , such as, for example, a switch or other suitable control element, is connected via an electrical line  136  to electronic control unit  80 . The parking brake can be actuated by means of electrical actuating device  134 . Therefore, by means of electrical actuating device  134 , the parking brake can be engaged or released or held in a partly engaged condition. 
     Electronic control unit  80  is connected via further electrical lines  138  to a modulator  140  for modulating compressed air at spring-actuator part  86  ( FIG. 3 ) of combination spring-actuated/diaphragm cylinders  84 . 
       FIG. 3  shows the construction of modulator  140 . Modulator  140  is in communication with first compressed air reservoir tank  116  and second compressed air reservoir tank  130 . From compressed air reservoir tanks  116 ,  130 , compressed air passes via compressed air lines  142 ,  144 ,  146  to inlet  148  of an air-flow-boosting valve device  150 , which is designed, for example, as a relay valve. Air-flow-boosting valve device  150  is protected by means of check valves  152 ,  154  from leaks in compressed air reservoir tanks  116 ,  130  or in compressed air lines  142 ,  144 . Check valves  152 ,  154  ensure that compressed air cannot escape in uncontrolled manner at inlet  148  of air-flow-boosting valve device  150  in the event of damage in the region of compressed air reservoir tanks  116 ,  130  or their supply to modulator  140 . 
     An outlet  156  of air-flow-boosting valve device  150  leads, via compressed air lines  158 ,  160 , to spring-actuator part  86  of spring-actuated/diaphragm cylinder  84 . 
     A control input  162  of the air-flow-boosting valve device leads to a solenoid valve  164 , which can be electrically actuated by control unit  80 . Valve  164  is in pneumatic communication via a compressed air line  166  with compressed air line  146  and, therefore, with compressed air reservoir tanks  116 ,  130 . By means of solenoid valve  164 , compressed air can be supplied in metered manner at control input  162  of air-flow-boosting valve device  150 . This supplied pressure has a maximum value equal to that of the pressure made available by compressed air reservoir tanks  116 ,  130 . By virtue of the design of solenoid valve  164 , however, it is also able to supply a lower pressure at control input  162  and, in particular, to vent control input  62  slowly or suddenly. 
     The pressure made available at control input  162  is reproduced by air-flow-boosting valve device  150  at its outlet  156 . However, the air flow made available with corresponding pressure by air-flow-boosting valve device  150  is substantially greater than the air flow supplied at control input  162 . By means of solenoid valve  164  and air-flow-boosting valve device  150 , a large air flow with high pressure can be made available at spring-actuator part  86  of the combination spring-actuated/diaphragm cylinders, in order to compress the actuator springs and, thus, release the parking brake. To the extent that the pressure at outlet  156  of air-flow-boosting valve device  150  is lowered, the spring actuators can relax and, thus, engage the parking brake. 
     For the purpose of venting, air-flow-boosting valve device  150  is in communication with a venting device  168 , via which the compressed air from spring-actuator part  86  can escape to atmosphere via compressed air line  158  and air-flow-boosting valve device  150 . Furthermore, solenoid valve  164  is also in communication with venting device  168 , to ensure that the pressure present at control input  162  of air-flow-boosting valve device  150  can escape. 
     Modulator  140  is further provided with three pressure sensors  170 ,  172 ,  174 , which each convert a measured pressure into an electrical signal and conduct these respective electrical signals to control unit  80  via electrical lines. These pressure sensors  170 ,  172 ,  174  are preferably disposed in a cover  176  of modulator  140  and, via pneumatic lines  178 ,  180 ,  182 , are in communication with their respective measuring points. 
     A first pressure sensor  170  measures the pressure of first compressed air reservoir tank  116 , albeit within modulator  140 . In another exemplary embodiment, however, it can also make its measurements outside modulator  140 , at another location. A second pressure sensor  172  measures the modulated pressure for the second brake circuit, meaning circuit II or front-axle brake circuit. A third pressure sensor  174  measures the pressure at outlet  156  of air-flow-boosting valve device  150  and, thus, the pressure supplied to spring-actuator part  86  of combination spring-actuated/diaphragm cylinder  84 . 
     In the event of failure of the first brake circuit (circuit I or rear axle brake circuit), the pressure measured by first pressure sensor  170  drops. Such a drop can be detected by comparison of the value measured by first pressure sensor  170  with a predefined minimum pressure value. If such a drop is detected, control unit  80  generates a control signal for solenoid valve  164 , so that solenoid valve  164  vents control input  162  of air-flow-boosting valve device  150 , with the result that spring-actuator part  86  of combination spring-actuated/diaphragm cylinder  84  is also vented. Thus, the spring actuator is pulled in, or, in other words, the parking brake is engaged, and, so, a braking action is achieved at the corresponding wheel brake, even though the service-brake circuit (circuit I or rear axle brake) to this wheel brake has failed and, thus, diaphragm part  88  of combination spring-actuated/diaphragm cylinder  84  can no longer be actuated. 
     In this way, the parking brake can also be used automatically to achieve the planned braking distance even in the event of failure of a brake circuit of the service brake. 
     The control signal supplied to solenoid valve  164  is determined as a function of the pressure value measured by second pressure sensor  172 . Specifically, second pressure sensor  172  determines a pressure value that corresponds to the braking intent of the vehicle operator, albeit for the second brake circuit (circuit II or front-axle brake circuit). This brake circuit is assumed to be still intact, and, so, the measured pressure value determined by second pressure sensor  172  is processed as a value that corresponds to the vehicle operator&#39;s braking intent. 
     A high pressure value of second pressure sensor  172  means intensive braking. Consequently, solenoid valve  164  is controlled by means of the solenoid-valve control signal such that rapid venting takes place at control input  162  of air-flow-boosting valve device  150  and, thus, spring-actuator part  86  is also vented rapidly. In this way, the spring actuator can be pulled in rapidly, allowing the actuator spring to exert a high force on the corresponding wheel brake. 
     When the vehicle operator&#39;s intent is only a small braking action, however, or, in other words, the pressure value measured by second pressure sensor  172  is small, the control signal at solenoid valve  164  is correspondingly adjusted, so that the pressure at control input  162  of air-flow-boosting valve device  150  is lowered only slightly. In this way, the pressure in spring-actuator part  86  is also reduced only slightly, and the braking action of the parking brake is only slight. 
     If the vehicle operator is no longer actuating brake actuating device  90 , or, in other words, is no longer expressing any braking intent, solenoid valve  164  regulates the pressure at control input  162  of air-flow-boosting valve device  150  back to a high value, so that spring-actuator part  86  is again pressurized with a high pressure. In this way, the parking brake can be released. 
     Second pressure sensor  172  is advantageously disposed in modulator  140  or in its cover  176 . Alternatively, however, it can be disposed at any other position of the second brake circuit, meaning, in particular, that it can also be disposed outside modulator  140  or its cover  176 . 
     Instead of or in addition to a signal of second pressure sensor  172 , the control signal for solenoid valve  164  can also be generated in another way, for example, as a function of a data signal representing braking intent of the vehicle operator. Such a data signal is used, for example, by an electronic brake system. It is typically a digital data signal, representing a value between 0 and 100%, for example. 
     Furthermore, the control signal for solenoid valve  164  can be generated additionally or alternatively as a function of a brake actuating signal, which can be generated by means of a displacement sensor disposed on brake actuating device  90 . The displacement signal detects the braking intent of the vehicle operator and converts it into an electrical signal. 
     Furthermore, the control signal for solenoid valve  164  can also be generated additionally or alternatively as a function of an electrical signal, which is passed to a proportional relay valve for control of the pressure in the second brake circuit. The electrical signal to the proportional relay valve can be, for example, the actuating current or the actuating voltage for actuating the proportional relay valve. 
     The braking intent of the vehicle operator can, therefore, be determined in diverse ways., which can be evaluated either individually or in any combination by control unit  80  and converted into a control signal for solenoid valve  164 . 
     By means of third pressure sensor  174 , it is possible to check the pressure at outlet  156  of air-flow-boosting valve device  150  or the pressure in spring-actuator part  86  of combination spring-actuated/diaphragm cylinder  84 . If the pressure measured by the third pressure sensor is not in agreement with the intended pressure value, the control signal to solenoid valve  164  can be adjusted appropriately. In this way, a closed regulating circuit is formed for setting the desired pressure in spring-actuator part  86 . 
       FIGS. 2 and 3  also show an overload-protection valve or select-high valve  184 , which is connected between outlet  156  of the air-flow-boosting valve device, a compressed air line  186  conveying the modulated pressure and compressed air line  160  to the spring-actuated brake cylinder. Overload-protection valve  184  selects the higher of the two pressures, namely, the modulated brake pressure or the pressure made available by the air-flow-boosting valve device, and it supplies the higher pressure to spring-actuator part  86  of combination spring-actuated/diaphragm cylinder  84 . Overload-protection valve  184  prevents addition of the brake force supplied by the service brake, or, in other words, via the pneumatic part or diaphragm part  88 , to the brake force supplied by the parking brake, or, in other words, spring-actuator part  86 , so that mechanical overloading of the brake mechanism of the wheel brake associated with this brake cylinder is prevented. By virtue of the illustrated structure, the brake force supplied to the brake cylinder via diaphragm part  88  is not increased by the brake force exerted by spring-actuator part  86 , since, in the case of actuation of the service brake, the brake force exerted by the actuator spring is reduced by a force corresponding to actuation of the service brake. In this way, critical overloading of the corresponding wheel brake can be avoided. 
     As discussed above in connection with  FIG. 2 , the brake system is provided with solenoid valves  100 ,  112 , which form the components of an anti-lock braking system. This anti-lock braking system is also controlled by control unit  80 . If one of wheel sensors  86  detects locking of one of wheels  74 , control unit  80  sends an electrical signal via an electrical line  188  to the corresponding solenoid valve  100 ,  112 , so that the brake pressure being supplied is reduced if necessary, in order to stop the locking of corresponding wheel  74 . 
     However, if the parking brake is being used to assist the service brake in the event of failure of the first brake circuit, anti-lock protection of the wheels of the corresponding axle is nevertheless ensured according to the present invention. For this purpose, the speed values of wheels  74  measured by speed sensors  76  are evaluated in control unit  80 . If it becomes evident, on the basis of the measured wheel speeds, that a wheel of the first brake circuit is locked, air is admitted to spring-actuator part  86  in order to release the parking brake. As soon as it becomes evident, on the basis of the measured wheel speed, that the wheel is again revolving with the speed corresponding to the vehicle speed, spring-actuator part  86  can be vented again in order to actuate the parking-brake function. 
     In this way, effective anti-lock protection can also be achieved by using the spring-actuated brakes instead of the service brake. 
     By virtue of the present invention it is possible to provide a simplified brake system that operates successfully without an inverting relay valve, but nevertheless, in the event of failure of the first brake circuit, provides an adequate braking action by means of the parking-brake function on the wheel brakes of this brake circuit. Furthermore, by virtue of the electrical control components used, anti-lock protection can be achieved even during braking by means of the parking-brake function. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               10  Brake system 
               12  Wheel 
               14  Wheel-speed sensor 
               16  Control unit 
               18  Electrical line 
               20  Brake cylinder 
               22  Brake actuating device 
               24  Compressed air line 
               26  Compressed air line 
               28  Compressed air line 
               30  Solenoid valve 
               32  Compressed air line 
               34  Compressed air line 
               36  Compressed air line 
               38  Compressed air line 
               40  Relay valve 
               42  Compressed air line 
               44  Solenoid valve 
               46  Compressed air line 
               48  Compressed air reservoir tank 
               50  Compressed air line 
               52  Compressed air line 
               54  Compressed air reservoir tank 
               56  Pneumatic switch 
               58  Compressed air line 
               60  Compressed air line 
               62  Compressed air line 
               64  Inverting relay valve 
               66  Valve 
               68  Compressed air line 
               70  Compressed air line 
               72  Brake system 
               74  Wheel 
               76  Wheel-speed sensor 
               78  Electrical line 
               80  Control unit 
               82  Brake cylinder 
               84  Brake cylinder 
               86  Spring-actuator part 
               88  Diaphragm part 
               90  Brake actuating device 
               92  Compressed air line 
               94  Compressed air line 
               96  Compressed air line 
               98  Valve 
               100  Solenoid valve 
               102  Compressed air line 
               104  Compressed air line 
               106  Compressed air line 
               108  Air-flow-boosting valve device 
               110  Compressed air line 
               112  Solenoid valve 
               114  Compressed air line 
               116  First compressed air reservoir tank 
               118  Compressed air line 
               120  Compressed air line 
               122  Compressed air line 
               124  Compressed air line 
               126  Compressed air line 
               128  Compressed air line 
               130  Second compressed air reservoir tank 
               132  Common compressed air reservoir 
               134  Electrical actuating device 
               136  Electrical line 
               138  Electrical line 
               140  Modulator 
               142  Compressed air line 
               144  Compressed air line 
               146  Compressed air line 
               148  Inlet 
               150  Air-flow-boosting valve device 
               152  Check valve 
               154  Check valve 
               156  Outlet 
               158  Compressed air line 
               160  Compressed air line 
               162  Control input 
               164  Solenoid valve 
               166  Compressed air line 
               168  Venting device 
               170  First pressure sensor 
               172  Second pressure sensor 
               174  Third pressure sensor 
               176  Cover 
               178  Pneumatic line 
               180  Pneumatic line 
               182  Pneumatic line 
               184  Overload-protection valve or select-high valve 
               186  Compressed air line 
               188  Electrical line