Patent Publication Number: US-2022227342-A1

Title: Electropneumatic control module

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of international patent application PCT/EP2020/080638, filed Nov. 2, 2020 designating the United States and claiming priority from German application 10 2019 130 762.7, filed Nov. 14, 2019, and the entire content of both applications is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to an electropneumatic control module for an electronically controllable pneumatic brake system of a vehicle, in particular utility vehicle, having a pneumatic supply port, which can be connected to a compressed air supply for the purposes of receiving a supply pressure, a trailer control unit, which has a trailer control valve unit with one or more electropneumatic valves, a trailer brake pressure port and a trailer feed pressure port, a holding brake unit, which has a spring-type actuator port for at least one spring-type actuator of the vehicle and has a holding brake pilot control unit with one or more electropneumatic valves, wherein a first holding brake pilot control port of the holding brake pilot control unit is connected to a vent, and having an electronic control unit, wherein the electronic control unit is configured to cause the holding brake unit to switch the holding brake pilot control unit into a ventilation position in response to the receipt of an electronic holding signal, wherein, in the ventilation position, a second holding brake pilot control port is connected in pressure-conducting fashion to the first holding brake pilot control port and the second spring-type actuator port is connectable to one of two vents. 
     BACKGROUND 
     In brake systems for vehicles that are configured for towing a trailer, the brake system has a trailer control unit, which is also referred to as a trailer control valve (TCV) and which is provided for pneumatically outputting the vehicle setpoint decelerations, which are specified by the vehicle, correspondingly also via ports, namely a trailer brake pressure port and a trailer feed pressure port. The trailer brake pressure port is also referred to as red coupling head, whereas the trailer feed pressure port is also referred to as yellow coupling head. The trailer or its brake system is supplied with a supply pressure, from a supply provided for this purpose in the towing vehicle, via the trailer feed pressure port, whereas the corresponding brake pressure is controlled via the trailer brake pressure port. 
     Brake systems of the above generic type have a holding brake unit, also referred to as an electropneumatic handbrake (EPH), as a further component or module. Such holding brake units are commonly operated with so-called spring-type actuators, that is, brake devices that brake one or more axles of the vehicle on the basis of a spring force. The brakes are released when pressurized, and are braked when ventilated. In an unpressurized state, the corresponding vehicle is thus braked. To activate the holding brake unit, an electrical switch is generally provided in the driver&#39;s cab of the vehicle, via which electrical switch a corresponding signal can be output to an electronic control unit, which then switches one or more electropneumatic valves such that the spring-type actuators are either ventilated or pressurized. 
     The holding brake unit, that is, the electropneumatic handbrake, is used for parking the vehicle or vehicle combination, but also as an additional brake in special situations. This means that, in addition to the normal service braking action, the spring-type actuators are at least partially ventilated in order for these to be additionally or alternatively used for braking. 
     Brake cylinders of the vehicle are commonly configured as double-acting brake cylinders. They have the task of generating the required braking forces for both the service brake and the holding brake system and, for this purpose, have several chambers that can be pressurized. The force of the double-acting brake cylinder is in this case generally transmitted to the corresponding wheel brake via a common actuating unit. If the service brake system and parking brake system are actuated at the same time, an addition of braking force occurs at the actuating unit and/or the wheel brake. This can result in overloading of and/or damage to the actuating unit and/or the wheel brake. Furthermore, if excessive braking forces are used, there is a risk of a loss of control of the vehicle, for example owing to locking wheels. If this is to be prevented, an overload protection function, which is also referred to as an anti-compounding function, must be provided. 
     In order for a movement of the vehicle to be prevented with a high degree of certainty when the vehicle is parked, it is furthermore desirable for the trailer to also be braked. Since the brake cylinders of trailers often do not have spring-type actuators, a positive brake pressure must be permanently provided to the brake cylinders of the trailer when the trailer is parked. In an unpressurized state, the trailer is movable, and in a pressurized state, the trailer is braked. The application of the braking force thus behaves inversely in the trailer and in the vehicle. In order to pneumatically output a corresponding brake signal for the trailer also, a so-called inverse relay valve is generally used, which outputs an increasing pressure for the trailer on the basis of a decreasing pressure in the spring-type actuators of the vehicle. Such inverse relay valves are of complex construction and commonly have multiple control pistons that interact with one another via different control surfaces and different control chambers, and are associated with high costs. Furthermore, it may also be provided that, as disclosed by the present applicant in US 2020/0079341, a parking brake valve unit having a pneumatically controlled switching valve is provided, which has a pneumatic control inlet for receiving a pneumatic control pressure. When a spring-type actuator port of the vehicle is connected to a pressure sink, the pneumatically controlled switching valve is switched such that a brake pressure can be output at the trailer brake pressure port. A disadvantage here is that, in order to implement an overload protection function, further pneumatic ports and/or additional lines have to be provided, which make the system more complicated and result in increased costs. 
     US 2020/0023820 discloses an electronically controllable brake system with a trailer control valve, which has a trailer control module, wherein the trailer control module is configured to receive and process an electronically transmitted braking specification, and the trailer control valve is configured to, in a manner controlled by the trailer control module, generate and output a redundancy control pressure in a manner dependent on the electronically transmitted braking specification, wherein, if an implementation of the braking specification, in a manner electrically controlled by a service brake control module, by way of at least one service brake circuit through the outputting of a service-brake brake pressure is prevented, the service-brake brake pressure can be generated, and output to the service brakes of the at least one service brake circuit, in a manner dependent on the redundancy control pressure generated in the trailer control valve, and/or a trailer control pressure can be generated, and output to a trailer, in a manner dependent on the redundancy control pressure generated in the trailer control valve. In order to prevent superposed braking owing to the simultaneous actuation of the service brakes and the spring brakes, it is proposed to provide corresponding open-loop and closed-loop control in a parking brake control module of the electronically controllable brake system. However, a cost-effective implementation of the overload protection function is not disclosed. 
     SUMMARY 
     It is an object of the present disclosure to specify an electropneumatic control module and an electronically controllable brake system having such a control module, which provides an overload protection function while being of simplified construction. A further object of the disclosure provides specifying a vehicle which has an electronically controllable brake system with such a control module. 
     The disclosure, for example, achieves the object, in the case of an electropneumatic control module of the type mentioned in the introduction, in that the holding brake unit is connected in pressure-conducting fashion to a redundancy port and is configured to, instead of a connection of the spring-type actuator port to the vent, output a first holding brake pressure at the spring-type actuator port if the holding brake pilot control unit is situated in the ventilation position and a redundancy pressure is provided at the redundancy port, wherein the trailer control unit is configured to output a brake pressure at the trailer brake pressure port if a redundancy pressure is provided at the redundancy port. 
     In the electropneumatic control module according to a first aspect of the disclosure, the redundancy port thus performs a dual function. Firstly, a brake pressure can be controlled at the trailer brake pressure port via the redundancy pressure provided at the redundancy port, and secondly, an overload protection function is implemented. The overload protection function includes that, in the presence of a redundancy pressure, a holding brake pressure is output at the spring-type actuator port even when the holding brake pilot control unit is situated in the ventilation position. In contrast, if no redundancy pressure is provided, a spring-type actuator that is fluidically connected to the spring-type actuator port is ventilated. An overload protection function and a redundancy function can thus be implemented with only one port, the redundancy port, and one port on the electropneumatic control module can be eliminated. This simplifies a construction of the electropneumatic control module, and the costs thereof can be reduced. 
     The outputting of a brake pressure at the trailer brake pressure port in the event that a redundancy pressure is provided is desirable, for example, if a user wishes to impart a braking demand or if there is a fault in the electrical system. For example, the electronic control unit may have a fault, or a voltage supply of the electropneumatic control module may be interrupted. The electropneumatic control module is preferably configured to output a brake pressure at the trailer brake pressure port if there is a fault in the electronic control unit, in one or more electropneumatic valves and/or in a voltage supply of the electropneumatic control module. In this way, the safety of a vehicle equipped with an electropneumatic control module according to the disclosure can be increased. 
     The overload protection function, also referred to as anti-compounding function, ensures that an actuating unit of a brake cylinder and/or a wheel brake is not fully actuated simultaneously by a spring-type actuator of the brake cylinder, which is connected to the spring-type actuator port, and a service brake cylinder. A spring-type actuator connected to the holding brake pilot control port is preferably ventilated when the holding brake pilot control unit is situated in a ventilation position and no redundancy pressure is provided. In this way, the force of the spring-type actuator is transmitted to the actuating unit of the brake cylinder and to a wheel brake connected thereto. If a redundancy pressure is now provided at the redundancy port, then the holding brake pilot control port is not connected to the vent, but rather a holding brake pressure is output, which at least partially counteracts the force of the spring-type actuator. The first holding brake pressure preferably corresponds to the redundancy pressure. However, it may also be provided that the holding brake pressure is proportional to the redundancy pressure. 
     In a first embodiment, the holding brake unit is configured to output the first holding brake pressure only if the holding brake pilot control unit is situated in the ventilation position, and to output the supply pressure if the holding brake pilot control unit is switched into an open position. The holding brake pilot control unit can thus be switched at least between a ventilation position and an open position. It should be understood that the holding brake pilot control unit may also have further switching positions, and/or that a pressure output by the holding brake pilot control unit in the open position can be modulated. The supply pressure preferably corresponds to a maximum pressure of the system. Furthermore, spring-type actuators connected to the spring-type actuator port are preferably fully pressurized when the supply pressure is output. 
     The spring-type actuator port is preferably connected to the vent if no redundancy pressure is provided at the redundancy port and the holding brake pilot control unit is situated in the ventilation position. The holding brake unit therefore preferably has a control function for the pressure provided at the spring-type actuator port. If the holding brake pilot control unit is situated in the ventilation position, the spring-type actuator port is either connected to the vent, or a first holding brake pressure is output. If the holding brake pilot control unit is now switched into the open position, the supply pressure is output at the spring-type actuator port, preferably even when a redundancy pressure is provided at the redundancy port. For parking of the vehicle, the holding brake pilot control unit is switched into the ventilation position. If, in this case, no redundancy pressure is provided at the redundancy port, the spring-type actuator port is connected to the vent and the spring-type actuator(s) of the vehicle is/are ventilated, such that the vehicle is braked. If a redundancy pressure is now provided at the redundancy port, then the first brake pressure is provided at the spring-type actuator port and the spring brake is thus at least partially released. 
     In an embodiment, the holding brake unit furthermore has a shuttle valve with a first shuttle valve port, a second shuttle valve port and a third shuttle valve port, wherein the first shuttle valve port is connected to the redundancy port for the purposes of receiving the redundancy pressure, the second shuttle valve port is connected to the holding brake pilot control unit for the purposes of receiving a pilot control pressure, and wherein the shuttle valve is configured to provide in each case the higher out of the redundancy pressure and the pilot control pressure at the third shuttle valve port. The shuttle valve, which is also referred to as a select-high valve, thus performs a selection function between the redundancy pressure and the pilot control pressure, which is provided by the holding brake pilot control unit. If a pressure prevails both at the first shuttle valve port and at the second shuttle valve port, the respectively higher pressure is output. The shuttle valve is preferably configured as a double check valve, wherein flow can pass through the double check valve only from the first shuttle valve port to the third shuttle valve port or from the second shuttle valve port to the third shuttle valve port. The selection function described above can be achieved in a particularly simple manner via a shuttle valve. The pilot control pressure is provided by the holding brake pilot control unit and may correspond to a pressure level of the vent, to the supply pressure and particularly preferably also to pressures lying between the pressure level of the vent and the supply pressure. 
     In an embodiment, the holding brake unit furthermore has a first relay valve, which has a control port connected to the third shuttle valve port and has a working port connected to the spring-type actuator port. Relay valves are generally configured to provide, at the working port, a pressure that is proportional to a control pressure provided at the control port. In this case, a pressure provided at a supply port is modulated so as to be proportional to the control pressure. According to this embodiment, a pressure output at the working port is therefore proportional to the redundancy pressure or to the pilot control pressure of the pilot control unit. If a control pressure provided at the control port corresponds to the pressure level of the vent, the working port of the relay valve and thus also the spring-type actuator port are connected in pressure-conducting fashion to a ventilation port of the relay valve. This may be the case for example if the holding brake pilot control unit is situated in the ventilation position and no redundancy pressure is provided at the redundancy port. 
     In one variant, the electropneumatic control module furthermore has a parking brake valve unit with a first pneumatically controlled switching valve which has a pneumatic control port for receiving a first pneumatic control pressure, wherein, when the spring-type actuator port is connected to the vent, the first pneumatically controlled switching valve is switched such that the supply pressure can be output at the trailer brake pressure port. A pneumatically controlled switching valve has the advantage that it can be switched even without energization. The first pneumatically controlled switching valve preferably has a first and a second switching position, wherein the first pneumatically controlled switching valve is switched into the first switching position when a first pneumatic control pressure is provided at the first pneumatic control port. The first pneumatically controlled switching valve is preferably preloaded into the second switching position, for example via a spring. 
     According to an embodiment, the first pneumatic control pressure is the pressure at the spring-type actuator port. If the spring-type actuator port is connected to the vent, spring-type actuators connected to the spring-type actuator port are ventilated, and the vehicle is braked. At the same time, the first pneumatically controlled switching valve is switched into the second switching position, such that a brake pressure is output at the trailer brake pressure port and a trailer connected to the vehicle is braked. By using the first pneumatically controlled switching valve, a simple construction can thus be achieved, which makes it possible to omit an inverse relay valve. A particularly simple, inexpensive and/or robust construction is hereby achieved. It is also the case that no further electropneumatic valve is required for this. 
     The first pneumatically controlled switching valve is preferably configured as a pneumatically controlled 3/2 directional valve with a first port, a second port and a third port. 3/2 directional valves are common switching valves that have three ports and two switching positions. Here, in the second switching position, the second port and the third port are connected, and the first port is closed. In the first switching position, the first and third ports are fluidically connected, and the second port is closed. 
     In an embodiment, the first port of the pneumatic 3/2 directional valve is connected to the redundancy port and the second port of the pneumatic 3/2 directional valve is connected to the supply port. A redundancy pressure can thus be output at the third port of the 3/2 directional valve if a first control pressure is provided at the pneumatic control port. Since the first control pressure corresponds to the pressure at the spring-type actuator port, this is the case when the spring-type actuators of a vehicle are at least partially pressurized. If the spring-type actuator port is connected to the vent, the first pneumatic control pressure corresponds to the pressure level of the vent, such that the first pneumatically switched switching valve is switched to the second switching position. In the second switching position, supply pressure is then provided at the third port of the 3/2 directional valve. 
     In a further embodiment, the third port of the pneumatically controlled 3/2 directional valve is connected to a redundancy valve of the trailer control valve unit of the trailer control unit. The redundancy valve of the trailer control valve unit is preferably an electronically controllable switching valve, in particular an electronically controllable 2/2 directional valve, which is open in a deenergized switching position. For example, the redundancy valve may be configured as a solenoid valve that is preloaded into the open switching position via a spring. The pressure provided at the redundancy valve is dependent here on the first pneumatic control pressure, which corresponds to the pressure at the spring-type actuator port. When the spring-type actuator port is connected to the vent, a supply pressure is provided at the redundancy valve. By contrast, if a pressure is output at the spring-type actuator port, then a redundancy pressure is provided at the redundancy valve. A brake pressure provided at the brake pressure port is preferably proportional to the pressure provided at the redundancy valve. It can thus advantageously be achieved that, for the purposes of braking a trailer, a supply pressure is provided at the brake pressure port when the spring-type actuator port is connected to the vent and the spring brakes are engaged. When a holding brake pressure is output at the spring-type actuator port, then the pneumatically controlled 3/2 directional valve switches to the first switch position, such that a redundancy pressure can be provided at the redundancy valve. It may also be provided that the redundancy valve is adapted to modulate a brake pressure that is provided at the trailer control port. 
     In a second variant, the trailer control valve unit of the trailer control unit has a redundancy valve, wherein the redundancy port is pneumatically connected to a redundancy valve port. Here, the redundancy port is thus permanently connected in fluid-conducting fashion to the redundancy valve. According to this variant, too, the redundancy valve is preferably configured as an electronically controllable directional valve, particularly preferably as a 2/2 directional valve, which is normally open. 
     According to an embodiment, the electropneumatic control module furthermore has a parking brake valve unit, wherein the electronic control unit is configured to cause the parking brake valve unit, on the basis of an electronic holding signal, to switch at least one valve of the parking brake valve unit such that a pneumatic connection between the trailer feed pressure port and the supply port is interrupted. This is desirable in particular in brake systems for the North American or Scandinavian markets, where trailers are often equipped with spring-type actuators which brake the trailer when ventilated. Furthermore, owing to legal regulations in the USA, the trailer feed pressure port and the trailer brake pressure port are configured to be open, such that it is necessary for an evacuation of the compressed-air supply to be prevented when no trailer is connected. The pneumatic connection is particularly preferably interrupted when the parking brake valve unit is deenergized. The parking brake valve unit is preferably configured to connect the trailer feed pressure port to the or a vent when the pneumatic connection of the trailer feed pressure port to the supply port is interrupted. 
     According to an embodiment, the parking brake valve unit has a second pneumatically controlled switching valve which has a second pneumatic control port for receiving a second pneumatic control pressure, wherein, if the second control pressure undershoots a second limit pressure, the second pneumatically controlled switching valve is switched such that the pneumatic connection between the trailer feed pressure port and the supply port is interrupted. Via pneumatic control, switching of the second pneumatic switching valve can be ensured even when the parking brake valve unit is deenergized. The second limit pressure preferably represents a switching threshold, wherein the second pneumatically controlled switching valve is switched when the switching threshold is overshot. The second control port is preferably connected to a first electronically controllable switching valve of the parking brake valve unit. The first electronically controllable switching valve is preferably configured as a 3/2 directional valve, wherein a first port of the 3/2 directional valve is connected to the control port. Preferably, in a first switching position, the first port of the 3/2 directional valve is connected via a throttle to the trailer feed pressure port. In a second switching position, the first port of the 3/2 directional valve is preferably connected to the vent, such that the pneumatic control module interrupts a connection between the trailer feed pressure port and the supply port when the 3/2 directional valve is switched to the second switching position. The 3/2 directional valve is preferably preloaded into the first switching state via a spring. If the trailer feed pressure port is ventilated, as may be the case for example if a leak occurs in a trailer brake circuit, then the pressure at the second pneumatic control port of the second pneumatically controlled switching valve decreases. Owing to the throttle, the pressure falls only slowly, such that the trailer feed pressure port is initially still connected to the supply port. If necessary, compressed air can be sufficiently replenished via the supply port to compensate for the pressure drop at the trailer feed pressure port. If the pressure at the trailer feed pressure port falls too low owing to a leak, then the second control pressure undershoots the limit pressure, and the connection between the supply port and the trailer feed pressure port is interrupted. 
     In a further embodiment, the second pneumatically controlled switching valve is configured as a pneumatically controlled 3/2 directional valve with a second port, a third port and a fourth port, wherein the second port is connected to the trailer feed pressure port, the third port is connected to the supply port, and the fourth port is connected to a or the vent. The pneumatically controlled 3/2 directional valve thus preferably has two switching positions, wherein, in a first switching position, the trailer feed pressure port connected to the second port is connected to the vent. The pneumatically controlled 3/2 directional valve is preferably preloaded into the second switching position. In a deenergized state of the second electropneumatic control module, the pneumatically controlled 3/2 directional valve is therefore preferably switched into the second switching position. In the second switching position, the supply port connected to the third port is fluidically connected to the second port and thus to the trailer feed pressure port. 
     The trailer control unit preferably has a third pneumatically controlled switching valve which has a third pneumatic control port for receiving a third pneumatic control pressure, wherein the third pneumatic control port of the third pneumatically controlled switching valve is connected in pressure-conducting fashion to the second pneumatic control port of the second pneumatic switching valve. Owing to the connection of the control ports of the second and third control ports, the second and third pneumatically controlled switching valves can be switched via a single control pressure. 
     In an embodiment, the third pneumatically controlled switching valve is configured to provide a trailer control pressure at the trailer brake pressure port if the control pressure overshoots a third limit pressure. The third limit pressure preferably corresponds to the second limit pressure. However, it should be understood that the third limit pressure for switching the third pneumatically controlled switching valve may differ from the second limit pressure. The third pneumatically controlled switching valve preferably interrupts a connection of the trailer control unit to the trailer brake pressure port when the third control pressure is lower than the third limit pressure. The third control pressure preferably falls below the third limit pressure when a pressure at the trailer feed pressure port corresponds to the pressure level of the vent. In this way, it is possible to prevent a brake pressure from being output at the trailer brake pressure port when no supply pressure is provided at the trailer feed pressure port. This function is also referred to as a tractor protection function. 
     According to an embodiment, the electronic control unit, the trailer control unit and the holding brake unit are integrated in one module. Provision may also be made for individual components, that is, the electronic control unit, the trailer control unit and/or the holding brake unit, to be in the form of sub-modules that are connectable to one another. By integrating the components in one module, the assembly process in particular is significantly simplified, whereby assembly costs can be saved. 
     The electropneumatic control module particularly preferably has a common housing in which at least the components of the electronic control unit, the trailer control unit and the holding brake unit are arranged. Assembly and/or production costs for the electropneumatic control module can be further reduced via a common housing. Furthermore, the complexity of an associated brake system can be reduced by way of a modular configuration and/or a common housing. For example, the risk of incorrectly connecting the electropneumatic control module during the assembly process is reduced. 
     According to a second aspect, the disclosure achieves the object stated in the introduction via an electronically controllable pneumatic brake system for a vehicle, in particular utility vehicle, having a front axle brake circuit for a front axle of the vehicle, which has a front axle modulator and front axle service brake cylinders, a rear axle brake circuit for at least one rear axle of the vehicle, which has a rear axle modulator and rear axle service brake cylinders, a trailer brake circuit, a central control unit which is configured to provide at least one control signal to the rear axle modulator and/or to the front axle modulator, and an electropneumatic control module according to one of the above-described embodiments according to the first aspect. With regard to the features of the electropneumatic control module, reference is made to the above explanations relating to the first aspect of the disclosure in their entirety. The front axle modulator is configured to provide a front axle brake pressure at the front axle service brake cylinders. The rear axle modulator is analogously configured to provide a rear axle brake pressure at the rear axle service brake cylinders. However, provision may also be made for one or more ABS control modules for an anti-lock brake system to be arranged between the front axle modulator and the front axle service brake cylinders and/or the rear axle modulator and the rear axle service brake cylinders. Such ABS control modules are known to a person skilled in the art from the relevant prior art. The electronically controllable pneumatic brake system preferably has a brake signal transmitter. The brake signal transmitter may be an electric brake pedal, which is configured to provide an electronic braking specification to the central control unit. Furthermore, the brake signal transmitter may also be a pneumatic brake signal transmitter for providing a pneumatic braking specification. 
     In a first embodiment of the electronically controllable pneumatic brake system, the redundancy port of the electropneumatic control module is pneumatically connected to the front axle modulator, to the rear axle modulator and/or to a manually actuatable brake signal transmitter. In this way, a front axle brake pressure, a rear axle brake pressure and/or a manually specified brake pressure can be used as redundancy pressure. 
     The redundancy pressure is particularly preferably a front axle brake pressure that is provided by the front axle modulator for the purposes of braking wheels of the front axle. If the service brakes of the rear axle cannot be used owing to a fault in the rear axle brake circuit, the use of the front axle brake pressure as redundancy pressure allows the wheels of the rear axle to be braked via the spring brakes. In this way, redundancy for the rear axle brake circuit can advantageously be achieved. 
     Provision may also be made for the redundancy pressure to be a front axle control pressure that is provided at the front axle modulator by the brake signal transmitter. Here, too, redundancy of the rear axle brake circuit is realized, wherein it is additionally achieved that the redundancy pressure is independent of a functionality of the front axle modulator. Furthermore, in a redundancy situation, the wheels of the front axle can be braked independently of the wheels of the rear axle. 
     In a third aspect, the disclosure achieves the object mentioned in the introduction via a vehicle, in particular a utility vehicle, with an electronically controllable pneumatic brake system according to the second aspect of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  is a schematic illustration of a vehicle with an electronically controllable pneumatic brake system which has an electropneumatic control module; 
         FIG. 2  shows an electropneumatic control module according to a first embodiment; and, 
         FIG. 3  shows an electropneumatic control module according to a second embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A vehicle  200 , in particular a utility vehicle  202 , has an electronically controllable pneumatic brake system  204  ( FIG. 1 ). The electronically controllable brake system  204  has in this case a front axle brake circuit  206 , a rear axle brake circuit  208  and a trailer brake circuit  209 . The front axle brake circuit  206  has a front axle modulator  210 , which is configured to output a front axle brake pressure pBV for front axle service brake cylinders  214 . 1 ,  214 . 2 . A first front axle service brake cylinder  214 . 1  is configured to brake a right front wheel  220 . 1  and the second service brake cylinder  214 . 2  is configured to brake a left front wheel  220 . 2  of a front axle VA of the vehicle  200 . Furthermore, the front axle brake circuit  206  in this case has ABS modules  222 . 1 ,  222 . 2 , which are configured to modulate the front axle brake pressure pBV, such that the front wheels  220  can be braked individually. Wheel rotational speed sensors  224 . 1 ,  224 . 2  are also provided for ascertaining a wheel rotational speed of the front wheels  220 . In this embodiment, the electronically controllable pneumatic brake system  204  furthermore has a manually actuatable brake signal transmitter  226 , wherein the brake signal transmitter  226  is configured to provide a front axle control pressure pSV that is proportional to a braking specification BV. A first compressed air supply  228  supplies compressed air both to the front axle modulator  210  and to the brake signal transmitter  226 . Here, the brake signal transmitter  226  is a partially electrical brake signal transmitter  230 , which, in addition to the front axle control pressure pSV, also provides control signals S 1 . 1 , S 1 . 2  that are proportional to the braking specification BV. 
     The rear axle brake circuit  208  is provided for braking right rear wheels  232 . 1  and left rear wheels  232 . 2  of the rear axle HA of the vehicle  200 . In this embodiment, the vehicle  200  has a total of four rear wheels  232 . 1 ,  232 . 2 ,  232 . 3 ,  232 . 4 . It should be understood that the vehicle  200  may also have only two rear wheels  232 . Furthermore, provision may also be made for the vehicle  200  to have a second rear axle (not illustrated), wherein the rear axle brake circuit  208  is preferably configured to brake the rear wheels  232  of both rear axles HA. To brake the rear wheels  232 , the rear axle brake circuit  208  has rear axle service brake cylinders  216 . 1 ,  216 . 2 , wherein a rear axle modulator  212  of the rear axle brake circuit  208  provides a rear axle brake pressure pBH at the rear axle service brake cylinders  216 . 1 ,  216 . 2 . Here, the rear axle service brake cylinders  216 . 1 ,  216 . 2  are connected, without ABS modules, to the rear axle modulator  212 . However, provision may also be made for the rear axle brake circuit  208  to include ABS modules. Wheel rotational speed sensors  224 . 3 ,  224 . 4  are provided for determining the rotational speed of the rear wheels  232 . The wheel rotational speed sensors  224 . 1 ,  224 . 2 ,  224 . 3 ,  224 . 4  are connected via signal lines  234 . 1 ,  234 . 2 ,  234 . 3 ,  234 . 4  to a central control unit  218  of the electronically controllable pneumatic brake system  204 , and provide wheel rotational speed data to the central control unit  218 . To control the ABS modules  222 . 1 ,  222 . 2 , the central control unit  218  is connected via control lines  238 . 1 ,  238 . 2  to the ABS modules  222 . 1 ,  222 . 2  and provides ABS signals S 3 . 1 , S 3 . 2 . Here, the control unit  218  and the rear axle modulator  212  are implemented as a combined module  236 . An embodiment as a combined module  236  allows simplified assembly and cost savings. It should be understood that the central control unit  218  and the rear axle modulator  212  may also be implemented as separate modules. A second compressed air supply  240  supplies the rear axle brake circuit  208  with compressed air. Here, the rear axle brake circuit  208  is electronically controllable, wherein the rear axle modulator  212  modulates the rear axle brake pressure pBH on the basis of rear axle control signals (not illustrated) from the central control unit  218 . The rear axle control signals are based here on the control signal S 1 . 2  that is provided by the brake signal transmitter  226  to the central control unit  218 . However, provision may also be made for the control signal S 1 . 2  of the brake signal transmitter  226  to be provided directly to the rear axle modulator  212 , and for the rear axle modulator to be configured to modulate the rear axle brake pressure pBH using the control signal S 1 . 2 . 
     In this embodiment, the rear axle service brake cylinders  216 . 1 ,  216 . 2  and spring-type actuators  242 . 1 ,  242 . 2  of the rear axle HA are combined in double-acting brake cylinders  244 . 1 ,  244 . 2 . The spring-type actuators  242 . 1 ,  242 . 2  are assigned to a parking brake circuit  211  and are connected to a spring-type actuator port  18  of an electropneumatic control module  1 . To release the spring-type actuators  242 . 1 ,  242 . 2 , the electropneumatic control module  1  outputs a first holding brake pressure pF 1  or a supply pressure pV at the spring-type actuator port  18  and thus pressurizes the spring-type actuators  242 . 1 ,  242 . 2 . Furthermore, the electropneumatic control module  1  is configured to ventilate the spring-type actuators  242 . 1 ,  242 . 2  via the spring-type actuator port  18 , such that the rear wheels  232  are braked via the spring-type actuators  242 . 1 ,  242 . 2 . This preferably occurs when a parking brake switch  246  is actuated. It should be understood that the parking brake switch  246  encompasses all types of actuating devices, such as pushbuttons or levers. Here, the parking brake switch  246  is an electronic switch  248  which, in response to being actuated by a user, provides an electronic holding signal S 2  to the electropneumatic control module  1 . 
     Furthermore, the electropneumatic control module  1  is also assigned to a trailer brake circuit  209  and is configured to output a brake pressure pB at a trailer brake pressure port  12  and a supply pressure pV at a trailer feed pressure port  14 . The trailer brake pressure port  12  and the trailer feed pressure port  14  are provided for the connection of a trailer (not illustrated). For the supply of supply pressure pV, a supply port  10  of the electropneumatic control module  1  is connected in pressure-conducting fashion to a third compressed air supply  250 . An electronic control unit ECU (not illustrated in  FIG. 1 , cf.  FIGS. 2 and 3 ) of the electropneumatic control module  1  is preferably connected to the central control unit  218 . Furthermore, the electropneumatic control module  1  has a redundancy port  20  which is connected here in pressure-conducting fashion to the brake signal transmitter  226 , wherein the brake signal transmitter  226  provides the front axle control pressure pSV at the redundancy port  20 . Provision may however also be made for the redundancy port  20  to be connected in pressure-conducting fashion to the rear axle modulator  212 , wherein the rear axle modulator provides the rear axle brake pressure pBH at the redundancy port  20 . The front axle modulator  10  may likewise preferably be connected in pressure-conducting fashion to the redundancy port  20  and provide the front axle brake pressure pBV there. 
     Furthermore, the electropneumatic control module  1  has a vent  16  which, in this case, is open to the environment. Altogether, the electropneumatic control module  1  has six ports, namely the supply port  10 , the trailer brake pressure port  12 , the trailer feed pressure port  14 , the vent  16 , the spring-type actuator port  18  and the redundancy port  20 . However, provision may also be made for the electropneumatic control module  1  to have multiple spring-type actuator ports  18 . 
       FIG. 2  shows a first embodiment of the electropneumatic control module  1 , which has a trailer control unit TCV, a holding brake unit EPH and a parking brake valve unit  40 . The trailer control unit TCV, the holding brake unit EPH and the parking brake valve unit  40  are in this case integrated into a common housing  26 . The trailer control unit TCV, which is also referred to as trailer control valve, and the holding brake unit EPH are configured here to be electronically controllable, and are connected to the electronic control unit ECU. The parking brake valve unit  40  has a first pneumatically controlled switching valve  42 , which can be controlled via a first control pressure pS 1  provided at a first pneumatic control port  42 . 1 . 
     The first pneumatic control port  42 . 1  is connected in pressure-conducting fashion to the spring-type actuator port  18 , such that the first control pressure pS 1  is equivalent to a pressure provided at the spring-type actuator port  18 . Here, the first pneumatically controlled switching valve  42  is configured as a pneumatically controlled 3/2 directional valve  44  which has a first port  44 . 1 , a second port  44 . 2  and a third port  44 . 3 . The first port  44 . 1  is connected in pressure-conducting fashion via a first redundancy branch  45 . 1  to the redundancy port  20 , at which a redundancy pressure pR can be provided. The second port  44 . 2  is connected in pressure-conducting fashion to the supply port  10 , which provides the supply pressure pV at the second port  44 . 2 . The third port  44 . 3  is connected in pressure-conducting fashion to a redundancy valve  30  of the trailer control unit TCV. The pneumatically controllable 3/2 directional valve  44  is preloaded in spring-loaded fashion into the first switching position illustrated in  FIG. 2 . In the first switching position, the second port  44 . 2  is connected in pressure-conducting fashion to the third port  44 . 3 , such that supply pressure pV is provided at the redundancy valve  30  of the trailer control unit TCV. If the first control pressure pS 1  overshoots a first limit pressure pG 1 , then the first pneumatically controllable switching valve  42  switches into a second switching position and connects the redundancy port  20  in pressure-conducting fashion to the redundancy valve  30 . The first limit pressure pG 1  is higher than a pressure level prevailing at the vent  16 , which in this case corresponds to an ambient pressure pU. If the spring-type actuator port  18  is ventilated through a pressure-conducting connection to the vent  16 , then holding brakes of the vehicle  200  are engaged. At the same time, the first control pressure pS 1  undershoots the first limit pressure pG 1  and the first pneumatically controllable switching valve  42  switches to the first switching position, such that supply pressure pV is provided to the redundancy valve  30  via the supply port  10 , the second port  44 . 2  and the third port  44 . 3 . By contrast, if a supply pressure pV or a holding brake pressure pF 1  that is higher than the first limit pressure pG 1  is provided at the spring-type actuator port  18 , then the spring-type actuators  242 . 1 ,  242 . 2  are at least partially pressurized, such that the spring-type actuators  242 . 1 ,  242 . 2  are at least partially released. At the same time, the pneumatically controlled switching valve  42  is switched to the second switching position, and the redundancy port  20  is connected to the redundancy valve  30  via the first port  44 . 1  and the third port  44 . 3  of the pneumatically controlled 3/2 directional valve  44 . 
     A particular advantage of the described embodiment is that, if spring-type actuators  242 . 1 ,  242 . 2  are to be engaged by pressure-conducting connection of the spring-type actuator port  18  to the vent  16 , supply pressure pV is automatically provided at the trailer control unit TCV. No expensive and bulky inverse relay valve is required for this purpose. 
     The redundancy valve  30  is assigned here to a trailer pilot control unit  29  of the trailer control unit TCV, which furthermore includes an inlet valve  32  and an outlet valve  33 . Furthermore, the trailer control valve unit  2  has a second relay valve  34 . The inlet valve  32  is configured as a 2/2 directional valve and has a first inlet valve port  32 . 1  and a second inlet valve port  32 . 2 . The first inlet valve port  32 . 1  is connected to the supply port  10  via a first supply branch  35 . 1  of a first supply distribution line  35 . The second inlet valve port  32 . 2  is connected to a first control line  36  of the trailer control unit TCV. The inlet valve  32  is configured to modulate a supply pressure pV, which is provided at the first inlet valve port  32 . 1 , on the basis of a first valve control signal SV 1  that is provided by the electronic control unit ECU. The inlet valve then provides a first control pressure pS 1  at the second inlet valve port  32 . 2  and in the first control line  36 . In the deenergized state, the inlet valve  32  is preloaded into a closed state. 
     A control inlet  34 . 1  of the second relay valve  34  is connected to the first control line  36 . The second relay valve  34  furthermore has a working port  34 . 2 , a supply port  34 . 3  and a ventilation port  34 . 4 . Here, the ventilation port  34 . 4  is connected to the vent  16 . The supply port  34 . 3  is connected to a second supply branch  35 . 2  of the supply pressure distribution line  35 , and is configured to receive the supply pressure pV provided at the supply port  10 . Furthermore, a third supply branch  35 . 3  of the supply pressure distribution line  35  connects the trailer feed pressure port  14  directly to the supply port  10  of the electropneumatic control module  1 . If the second relay valve  34  receives the first control pressure pS 1  at the control port  34 . 1 , then the second relay valve outputs a brake pressure pB, which is proportional to the first control pressure pS 1 , at the working port  34 . 2 , and provides the brake pressure to the trailer brake pressure port  12  via a trailer brake pressure line  37 . It should be understood that the brake pressure pB may also be identical to the control pressure pS 1 . Likewise, provision may also be made for the brake pressure pB to be a multiple of the first control pressure pS 1 . Here, the trailer control unit TCV furthermore has a pressure sensor  38  which is connected to the electronic control unit ECU and which is configured to provide a pressure signal SD, which corresponds to the pressure in the trailer brake pressure line  37 , to the electronic control unit ECU. 
     A first outlet valve port  33 . 1  of the outlet valve  33  is connected to the first control line  36 . The outlet valve  33  is electrically switched, and can be switched from a closed switching state shown in  FIG. 2  into an open switching state in response to receiving a second valve control signal SV 2  that is provided by the electronic control unit ECU. In the open switching state, the outlet valve  33  connects the first control line  36  to the vent  16 , wherein the first outlet valve port  33 . 1  is connected in pressure-conducting fashion to a second outlet valve port  33 . 2 . In a deenergized state, the outlet valve  33  is preferably preloaded into the switching state shown in  FIG. 2  and closed. If the outlet valve  33  is opened, the pressure in the first control line  36  and at the control port  34 . 1  of the second relay valve  34  drops to the ambient pressure pU of the vent  16 . In this way, the second relay valve  34  is also switched into a ventilation position, such that the trailer brake pressure line  37  and the trailer brake pressure port  12  are ventilated via the ventilation port  34 . 4  of the second relay valve  34 . 
     The second relay valve  34  is controlled purely pneumatically. If the inlet valve  32  and the outlet valve  33  are deenergized owing to a fault in the electronic control unit ECU and/or a fault in a voltage supply (not shown) of the electropneumatic control module  1 , then these close automatically, such that no first control pressure pS 1  is provided by the inlet valve  32  to the first control line  36 . The redundancy valve  30 , which in this case is likewise electrically switched, is open in a deenergized state shown in  FIG. 2 , such that a first redundancy valve port  30 . 1  is connected in pressure-conducting fashion to a second redundancy valve port  30 . 2 . The second redundancy valve port  30 . 2  is in turn connected to the first control line  36 . If the trailer pilot control unit  29  is deenergized, the inlet valve  32  and the outlet valve  33  are closed, whereas the redundancy valve  30  is open. Thus, a pressure provided at the first redundancy valve port  30 . 1  can be provided at the control port  34 . 1  of the second relay valve  34 . It should be understood that the redundancy valve  30  may also be configured to modulate a pressure provided at the first redundancy valve port  30 . 1  on the basis of a corresponding third valve control signal SV 3 , and to provide a correspondingly modulated pressure at the second redundancy valve port  30 . 2 . 
     The pressure that is provided at the first redundancy valve port  30 . 1  is determined by the parking brake valve unit  40 , as discussed above. Depending on the switching position of the parking brake valve unit  40 , either a redundancy pressure pR is provided to the redundancy valve  30  via the first port  44 . 1  and the third port  44 . 3  of the parking brake valve unit  40 , or a supply pressure pV is provided to the redundancy valve  30  via the second port  44 . 2  and the third port  44 . 3 . When the redundancy valve  30  is open, then the redundancy pressure pR is also provided at the control port  34 . 1  of the second relay valve  34 . In the deenergized situation, and if the parking brake valve unit  40  is in a corresponding switching position, then a brake pressure pB that is proportional, particularly preferably equivalent, to the redundancy pressure pR is provided at the trailer brake pressure port  12 . The corresponding switching position is present if, at the spring-type actuator port  18 , a pressure pF 1 , pV is provided that is greater than the first limit pressure pG 1  of the first pneumatic control port  42 . 1  of the first pneumatically controlled switching valve  42  of the parking brake valve unit  40 . It is thus possible for a brake pressure pB that is proportional to the redundancy pressure pR to be output at the trailer brake pressure port  12  precisely when the spring-type actuators  242 . 1 ,  242 . 2  of the vehicle  200  are released. If the spring-type actuators  242 . 1 ,  242 . 2  of the vehicle  200  are ventilated, such that the vehicle  200  is braked, the pressure level of the vent  16 , which corresponds here to the ambient pressure pU, prevails at the spring-type actuator port  18  and at the pneumatic control port  42 . 1 . The first limit pressure pG 1  of the pneumatically controlled switching valve  42  is higher than the ambient pressure pU, such that the switching valve  42  is switched into the switching position shown in  FIG. 2 . In the switching position shown, the second port  44 . 2  of the pneumatically controlled 3/2 directional valve  44  is connected in pressure-conducting fashion to the third port  44 . 3 . Supply pressure pV can thus be provided at the first redundancy valve port  30 . 1  via the supply port  10 , a fourth supply branch  35 . 4 , the supply distribution line  35 , the second and third ports  44 . 2 ,  44 . 3  of the first pneumatically controlled switching valve  42 , and a redundancy line  39 . If the redundancy valve  30  is open, then the supply pressure pV is provided via the first control line  36  to the control port  34 . 1  of the second relay valve  34 , which then provides, at the working port  34 . 2  and thus also at the trailer brake pressure port  12 , a brake pressure pB that is proportional to the supply pressure pV. It can advantageously be achieved in this way that, if the spring brakes of the vehicle  200  are engaged, that is, the spring-type accumulators are fully ventilated, a brake pressure pB that is proportional to the supply pressure pV, preferably a brake pressure pB that is equivalent to the supply pressure pV, is provided at the trailer brake pressure port  12 . This functionality is implemented here without an expensive inverse relay valve. Furthermore, this is also possible when the electropneumatic control module  1  is deenergized, for example when the vehicle  200  is parked. It should be understood that the inlet valve  32  and the outlet valve  33  may also be closed on the basis of corresponding first and second valve control signals SV 1 , SV 2 . Likewise, the redundancy valve  30  may also be opened on the basis of the third valve control signal SV 3  provided by the electronic control unit ECU. However, the redundancy valve  30  is preferably closed in normal operation, such that the brake pressure pB can be output solely via the first control pressure pS 1  provided by the inlet valve  32 . 
     The pressure pF 1 , pV, pU provided at the spring-type actuator port  18  is determined by the holding brake unit EPH. The holding brake unit EPH has a holding brake pilot control unit  4 , which is formed here by an electropneumatic bistable valve  46  and a second parking brake valve  48  and which is configured to provide a pilot control pressure pVS. A first holding brake pilot control port  4 . 1  of the holding brake pilot control unit  4  is formed here by a first port  46 . 1  of the bistable valve  46 . A third port  46 . 3  of the bistable valve  46  forms a third holding brake pilot control port  4 . 3 . A second port  48 . 2  of the second holding brake valve  48  is in this case a second holding brake pilot control port  4 . 2 , at which the pilot control pressure pVS is provided. A second port  46 . 2  of the bistable valve  46  is connected in pressure-conducting fashion to a first port  48 . 1  of the second holding brake valve  48 . The second holding brake valve  48  is electropneumatically controlled and is preloaded into the open switching position illustrated in  FIG. 2 . The second holding brake valve  48  can be closed on the basis of fourth valve control signals SV 4 , which are provided by the electronic control unit ECU. The first port  46 . 1  of the bistable valve  46  and thus also the first holding brake pilot control port  4 . 1  are connected to the vent  16 . The third port  46 . 3  of the bistable valve  46  and thus also the holding brake pilot control port  4 . 3  are connected via a fifth supply branch  35 . 5  to the supply port  10 , such that supply pressure pV can be provided at the third holding brake pilot control port  4 . 3 . The bistable valve  46  is configured as a conventional bistable 3/2 directional valve with two stable switching states, and can be switched between the two switching states on the basis of a fifth valve control signal SV 5 . In response to receiving an electronic holding signal S 2 , the electronic control unit ECU provides valve control signals SV 4 , SV 5  and switches the holding brake pilot control unit  4 . In the ventilation position  22  shown in  FIG. 2 , the first holding brake pilot control port  4 . 1  is connected in pressure-conducting fashion to the second holding brake pilot control port  4 . 2  and thus also to the vent  16 . In the open position  24 , the second holding brake valve  28  is open and a second port  46 . 2  of the bistable valve  46  is connected in pressure-conducting fashion to the third port  46 . 3 . The supply pressure pV provided via the fifth supply branch  35 . 5  is thus provided by the third holding brake pilot control port  4 . 3  to the second holding brake pilot control port  4 . 2 . The pilot control pressure pVS is thus output at the second holding brake pilot control port  4 . 2  in a manner dependent on the switching position  22 ,  24  of the holding brake pilot control unit  4 . In the ventilation position  22 , the pilot control pressure pVS corresponds to the pressure at the vent  16 , which corresponds here to the ambient pressure pU. In the open position  24 , the pilot control pressure pVS corresponds to the supply pressure pV. 
     The holding brake unit EPH furthermore has a shuttle valve  50 , which is configured here as a double check valve  52 . A first shuttle valve port  50 . 1  of the shuttle valve  50  is connected via a second redundancy branch  45 . 2  to the redundancy port  20 . Furthermore, the shuttle valve  50  has a second shuttle valve port  50 . 2  and a third shuttle valve port  50 . 3 . A pilot control line  54  connects the second holding brake pilot control port  4 . 2  to the second shuttle valve port  50 . 2 . It is thus possible for the redundancy pressure pR to be provided at the first shuttle valve port  50 . 1  and for the pilot control pressure pVS to be provided at the second shuttle valve port  50 . 2 . The shuttle valve  50  performs a selection function here, which is also referred to as a select-high function, wherein always the respectively higher of the pressures provided at the first and second shuttle valve ports  50 . 1 ,  50 . 2  is provided at the third shuttle valve port  50 . 3 . The third shuttle valve port  50 . 3  is connected to the control port  60 . 1  of a first relay valve  60  of the holding brake unit EPH. The first relay valve  60  is configured to output, at a working port  60 . 2 , a pressure that is proportional to the pressure prevailing at the control port  60 . 1 . For this purpose, the first relay valve  60  modulates the supply pressure pV that is provided at a feed port  60 . 3  via a sixth supply branch  35 . 6 . If the control port  60 . 1  of the first relay valve  60  is connected to the vent  16 , then the working port  60 . 2  is ventilated via a ventilation port  60 . 4 . A check valve  56  is preferably arranged in the sixth supply branch  35 . 6 , which check valve prevents fluid from flowing back from the feed port  60 . 3  to the supply port  10 . A spring-type actuator line  58  connects the working port  60 . 2  of the first relay valve  60  to the spring-type actuator port  18 . For corresponding closed-loop pressure control, a second pressure sensor  59  is provided for the holding brake unit EPH, which second pressure sensor is connected to the spring-type actuator line  58  and provides a corresponding second pressure signal SD 2  to the control unit ECU. 
     The holding brake pilot control unit  4  and the shuttle valve  50  determine the pressure that is provided at the working port  60 . 2  of the first relay valve  60  and thus also at the spring-type actuator port  18 . For this purpose, it is first of all decisive whether a redundancy pressure pR is provided at the first shuttle valve port  50 . 1  via the redundancy port  20  and the second redundancy pressure distribution line  45 . 2 . If this is not the case, the pressure output at the spring-type actuator port  18  is determined by the holding brake pilot control unit  4 . If the holding brake pilot control unit  4  is situated in the ventilation position  22 , then the ambient pressure pU is output at the spring-type actuator port  18 , and spring-type actuators connected to the spring-type actuator port  18  are ventilated. If the holding brake pilot control unit  4  is situated in an open position  24 , then the supply pressure pV is provided at the control port  60 . 1  of the first relay valve  60  via the second holding brake pilot control port  4 . 2 , the pilot control line  54 , the second shuttle valve port  50 . 2  and the third shuttle valve port  50 . 3 . The first relay valve  60  then outputs the supply pressure pV, or a second holding brake pressure pF 2  proportional to the supply pressure pV, at the working port  60 . 2  and thus at the spring-type actuator port  18 . 
     By contrast, if a redundancy pressure pR is provided at the redundancy port  20 , then this prevails directly at the first shuttle valve port  50 . 1  owing to the direct connection via the second redundancy pressure distribution line  45 . 2 . If the holding brake pilot control unit  4  is situated in the ventilation position, the ambient pressure pU is provided at the second shuttle valve port  50 . 2 . The shuttle valve  50  provides the higher pressure, that is, in this case the redundancy pressure pR, at the third shuttle valve port  50 . 3  and thus also at the control port  60 . 1  of the first relay valve  60 . The first relay valve  60  then provides a first holding brake pressure pF 1  at the working port  60 . 2  and at the spring-type actuator port  18  that is connected to the working port by the spring-type actuator line  58 . The holding brake pressure pF 1  preferably corresponds to the redundancy pressure pR. As a result, spring-type actuators  242 . 1 ,  242 . 2  of the vehicle  200  that are connected to the spring-type actuator port  18  are at least partially pressurized. If the redundancy pressure pR is also provided at service brake cylinders  216  of the vehicle  200 , simultaneous actuation of an actuating unit (not illustrated) and/or of a wheel brake (not illustrated) by spring-type actuator  242  and service brake cylinder  216  can thus be avoided, and an overload protection function can be implemented. 
     By contrast, if the holding brake pilot control unit  4  is situated in an open position, then the first pilot control pressure pVS prevails at the second shuttle valve port  50 . 2 . If the bistable valve  46  and the second holding brake valve  48  are fully open, then the first pilot control pressure pVS corresponds to the supply pressure pV. Since the supply pressure pV is higher than the redundancy pressure pR, the supply pressure is provided by the shuttle valve  50  to the control port  60 . 1  of the first relay valve  60 . Consequently, a pressure proportional to the supply pressure pV is provided at the spring-type actuator port  18 . This preferably corresponds to the supply pressure pV. 
     The second holding brake valve  48  is preferably configured to modulate a pressure provided at the second port  46 . 2  of the bistable valve  46 , and to provide the pressure at the second port  48 . 2  of the second holding brake valve  48 . 2 . The pilot control pressure pVS can thus be modulated via the second holding brake valve  48 . This is particularly advantageous if no redundancy pressure pR is provided at the first shuttle valve port  50 . 1 . As already discussed, the holding brake unit EPH then provides a second holding brake pressure pF 2 , which is proportional to the first pilot control pressure pVS, at the spring-type actuator port  18 . By modulation of the pressure pVS, spring brakes  242 . 1 ,  242 . 2  of the vehicle  200  that are connected to the spring-type actuator port  18  can thus be used as redundancy brakes or auxiliary brakes. However, provision may also be made for the holding brake pilot control unit  4  to be implemented without a second holding brake valve  48 . For example, the second holding brake pilot control port  4 . 2  may then be formed by the second port  46 . 2  of the bistable valve  46 . 
     According to this embodiment, both the trailer control unit TCV and the holding brake unit EPH are actuated by the electronic control module ECU. However, provision may also be made for the trailer control unit TCV and the holding brake unit EPH to have respectively dedicated electronic control units. This may be preferable in order to ensure at least the functionality of one subsystem in the event of a failure of the respective other electronic control unit. However, costs can preferably be saved through the use of one common electronic control unit ECU. 
     Here, the electropneumatic control module  1  has in each case only one supply port  10  and one redundancy port  20 , which in the electropneumatic control module  1  are connected to the valves via corresponding supply branches  35 . 1 ,  35 . 2 ,  35 . 3 ,  35 . 4 ,  35 . 5 ,  35 . 6  and redundancy branches  45 . 1 ,  45 . 2 . In this way, a very simple construction of the electropneumatic control module  1  can be implemented. Furthermore, assembly errors during the installation of the electropneumatic control module  1  into a brake system are avoided. Furthermore, simplified and inexpensive line routing can be achieved in a brake system  204  that has an electropneumatic control module  1  according to the disclosure. 
       FIG. 3  illustrates a second embodiment of an electropneumatic control module  1 . The holding brake unit EPH is of substantially analogous configuration to the holding brake unit EPH according to the first embodiment, for which reason reference is made here to the above description relating to the first embodiment in its entirety. In addition to the second pressure sensor  59 , the holding brake unit EPH according to the second embodiment also has a third pressure sensor  62 . It should be understood that the holding brake unit EPH according to the first embodiment ( FIG. 2 ) may also have a third pressure sensor  62 . 
     The trailer control unit TCV according to the second embodiment is also of substantially analogous configuration to the trailer control unit TCV according to the first embodiment. Here, however, the first redundancy valve port  30 . 1  of the redundancy valve  30  is connected to the redundancy port  20  via the first redundancy branch  45 . 1 . The functioning of the inlet valve  32 , of the outlet valve  33  and of the second relay valve  34  is substantially analogous to the first embodiment in this case. In the second embodiment, a third pneumatic switching valve  80  is also provided between the working port  34 . 2  and the trailer brake pressure line  37 , which third pneumatic switching valve is configured to pass a brake pressure pB provided at the working port  34 . 2  of the second relay valve  34  through to the trailer brake pressure port  12  only when a third control pressure pS 3  overshoots a third limit pressure pG 3  of the third pneumatic switching valve  80 . In an unpressurized state, the third pneumatic switching valve  80  is preloaded into a closed state shown in  FIG. 3 . A third control line  86  connects a third pneumatic control port  80 . 1  of the third pneumatic switching valve  80  to a second control port  70 . 1  of a second pneumatic switching valve  70  of the parking brake valve unit  40 . A second pneumatic control pressure pS 2  for controlling the second pneumatic switching valve  70  and the third pneumatic control pressure pS 3  are therefore identical. If the second pneumatic control pressure pS 2  overshoots a second limit pressure pG 2  of the second pneumatic control valve  70 , then the second pneumatic switching valve  70  is switched from the first switching position illustrated in  FIG. 3  into a second switching position. The second pneumatic switching valve  70  is preferably preloaded into the first switching position. The second pneumatic switching valve  70  is arranged between the third supply branch  35 . 3  and the trailer feed port  14 . Here, the third supply branch  35 . 3  is connected to a third port  70 . 3  of the second pneumatic control valve  70 . A second port  70 . 2  of the second pneumatic switching valve  70  is connected in pressure-conducting fashion to the trailer feed port  14 . If the second pneumatic switching valve  70  is situated in the second switching position, then the third port  70 . 3  and the second port  70 . 2  are connected, and supply pressure pV is provided at the trailer feed port  14 . By contrast, in the first switching position of the second pneumatic switching valve  70 , the trailer feed port  14  is connected via a fourth port  70 . 4  to the vent  16 . 
     To provide the second and third control pressure pS 2 , pS 3 , the parking brake valve unit  40  has a first parking brake valve  90  and a second parking brake valve  92 . Both the first parking brake valve  90  and the second parking brake valve  92  are configured here as electrically switchable valves. The first parking brake valve  90  is an electrically switchable 2/2 directional valve. The fourth supply branch  35 . 4  connects a first port  90 . 1  of the first parking brake valve  92  to the supply inlet  10 . The electronic control unit ECU is configured to provide sixth valve control signals SV 6  at the first parking brake valve  90 , wherein the first parking brake valve  90  is opened and provides the supply pressure pV 2  at the second port  90 . 2 . A second control line  84  connects the second port  90 . 2  of the first parking brake valve  90  to a first port  92 . 1  of the second parking brake valve  92  and to the third control line  86 . A second port  92 . 2  of the second parking brake valve  92  is connected to the trailer feed port  14 . Furthermore, a third port  92 . 3  of the second parking brake valve  92  is connected to the vent  16 . If the second parking brake valve  92  is switched from a first switching state to a second switching state on the basis of seventh valve control signals SV 7  that are provided by the electronic control unit ECU, then the second control line  84  and the third control line  86  are connected to the vent  16 . As a result, the second control pressure pS 2  falls below the second limit pressure pG 2 , and the second pneumatic control valve  70  switches into the first switching state, wherein the trailer feed port  14  is connected in pressure-conducting fashion to the vent  16 . Furthermore, the third control pressure pS 3  also falls below the third limit pressure pG 3 , such that the third pneumatic control valve  80  is closed, wherein no brake pressure pB is output at the trailer brake pressure port  12 . 
     In a first switching state of the second switching valve  92 , the first port  92 . 1  and the second port  92 . 2  are connected via a throttle  93 . Here, the second parking brake valve  92  is preloaded into the first switching state. The throttle  93  in this case allows only a comparatively slow pressure equalization between the first port  92 . 1  and the second port  92 . 2  of the second parking brake valve  92 . If a brake pressure pB is to be provided at the trailer brake pressure port  12  and a supply pressure pV is to be provided at the trailer feed pressure port  14 , the first parking brake valve  90  is switched into the second switching state and the supply pressure pV is output at the second port  90 . 2  of the first parking brake valve  90 . Since the throttle  93  of the second parking brake valve  92  allows only a slow pressure equalization, the pressure in the second and third control lines  84 ,  86  increases. As soon as the second control pressure pS 2  overshoots the second limit pressure pG 2 , the second pneumatic switching valve  70  switches into the second switching state and connects the supply port  10  in pressure-conducting fashion to the trailer feed pressure port  14 . Since the supply pressure pV is now provided both at the first port  92 . 1  and at the second port  92 . 2  of the second parking brake valve  92 , the pressure in the second and third control lines  84 ,  86  stabilizes at the level of the supply pressure pV. As soon as the third control pressure pS 3  overshoots the third limit pressure pG 3 , the third pneumatic switching valve  80  is opened, such that a brake pressure pB can be output at the trailer brake pressure port  12  via the second relay valve  34 . 
     A major function of the parking brake valve unit  40  according to the second embodiment includes protecting a pressure level in the electropneumatic control module  1  and in the electronically controllable brake system  204  in the event of a leak in a brake system of the trailer (not illustrated) or in the event of a sudden disconnection of the trailer from the trailer feed pressure port  14 . In such a situation, the trailer feed pressure port  14  is rapidly ventilated. If, in such a situation, the second pneumatic switching valve  70  were to remain in the first switching position, then the compressed air supply  250  connected to the supply port would be evacuated. This is avoided by way of the described arrangement of the first parking brake valve  90 , of the second parking brake valve  92 , of the second pneumatic switching valve  70  and of the third pneumatic switching valve  80 . If the trailer feed port  14  is ventilated, then the pressure of the second port  92 . 2 , which is connected thereto, of the second parking brake valve  92  falls to the level of the ambient pressure pU. Since the first port  92 . 1  and the second port  92 . 2  of the second parking brake valve  92  are connected via the throttle  93 , the pressure in the second and third control lines  84 ,  86  also falls. As soon as the second control pressure pS 2  undershoots the second limit pressure pG 2 , the second pneumatic switching valve is switched to the first switching position illustrated in  FIG. 3 , and a pressure-conducting connection of the trailer feed pressure port  14  to the supply port  10  is interrupted. Furthermore, a pressure-conducting connection of the working port  34 . 2  of the second relay valve  34  to the trailer brake pressure port  12  is prevented as soon as the third control pressure pS 3  undershoots the third limit pressure pG 3 . 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. 
     LIST OF REFERENCE DESIGNATIONS (PART OF THE DESCRIPTION) 
     
         
           1  Electropneumatic control module 
           2  Trailer control valve unit 
           4  Holding brake pilot control unit 
           4 . 1  First holding brake pilot control port 
           4 . 2  Second holding brake pilot control port 
           4 . 3  Third holding brake pilot control port 
           6  Electropneumatic valves of the trailer control valve unit 
           8  Electropneumatic valves of the holding brake pilot control unit 
           10  Supply port 
           12  Trailer brake pressure port 
           14  Trailer feed pressure port 
           16  Vent 
           18  Spring-type actuator port 
           20  Redundancy port 
           22  Ventilation position 
           24  Open position 
           26  Housing 
           29  Trailer pilot control unit 
           30  Redundancy valve 
           30 . 1  First redundancy valve port 
           30 . 2  Second redundancy valve port 
           32  Inlet valve 
           32 . 1  First inlet valve port 
           32 . 2  Second inlet valve port 
           33  Outlet valve 
           33 . 1  First outlet valve port 
           33 . 2  Second outlet valve port 
           34  Second relay valve 
           34 . 1  Control inlet of second relay valve 
           34 . 2  Working port of second relay valve 
           34 . 3  Feed port of second relay valve 
           34 . 4  Ventilation port of second relay valve 
           35  Supply distribution line 
           35 . 1 ,  35 . 2 ,  35 . 3 ,  35 . 4 , 
           35 . 5 ,  35 . 6  First to sixth supply branches 
           36  First control line 
           37  Trailer brake pressure line 
           38  Pressure sensor 
           39  Redundancy line 
           40  Parking brake valve unit 
           42  First pneumatically controlled switching valve 
           42 . 1  First pneumatic control port 
           44  Pneumatically controlled 3/2 directional valve 
           44 . 1  First port 
           44 . 2  Second port 
           44 . 3  Third port 
           44 . 4  Spring 
           45 . 1  First redundancy branch 
           45 . 2  Second redundancy branch 
           46  Bistable valve 
           46 . 1  First port of bistable valve 
           46 . 2  Second port of bistable valve 
           46 . 3  Third port of bistable valve 
           48  Second holding brake valve 
           50  Shuttle valve 
           50 . 1  First shuttle valve port 
           50 . 2  Second shuttle valve port 
           50 . 3  Third shuttle valve port 
           52  Double check valve 
           54  Pilot control line 
           56  Check valve 
           58  Second pressure sensor 
           60  First relay valve 
           60 . 1  Control port of first relay valve 
           60 . 2  Working port of first relay valve 
           60 . 3  Feed port of first relay valve 
           60 . 4  Ventilation port of first relay valve 
           62  Third pressure sensor 
           70  Second pneumatic switching valve 
           70 . 1  Second pneumatic control port 
           70 . 2  Second port of second pneumatic switching valve 
           70 . 3  Third port of second pneumatic switching valve 
           70 . 4  Fourth port of second pneumatic switching valve 
           80  Third pneumatic switching valve 
           80 . 1  Third control port 
           84  Second control line 
           86  Third control line 
           90  First parking brake valve 
           90 . 1  First port of first parking brake valve 
           90 . 2  Second port of first parking brake valve 
           92  Second parking brake valve 
           92 . 1  First port of second parking brake valve 
           92 . 2  Second port of second parking brake valve 
           92 . 3  Third port of second parking brake valve 
           93  Throttle 
           200  Vehicle 
           202  Utility vehicle 
           204  Electronically controllable pneumatic brake system 
           206  Front axle brake circuit 
           208  Rear axle brake circuit 
           209  Trailer brake circuit 
           210  Front axle modulator 
           211  Parking brake circuit 
           212  Rear axle modulator 
           214  Front axle service brake cylinder 
           214 . 1  First front axle service brake cylinder 
           214 . 2  Second front axle service brake cylinder 
           216 . 1 ,  216 . 2  Rear axle service brake cylinder 
           218  Central control unit 
           220  Front wheels 
           220 . 1  Right front wheel 
           220 . 2  Left front wheel 
           222 . 1 ,  222 . 2  ABS modules 
           224 . 1 ,  224 . 2 ,  224 . 3 , 
           224 . 4  Wheel rotational speed sensors 
           226  Brake signal transmitter 
           228  First compressed air supply 
           230  Partially electric brake signal transmitter 
           232  Rear wheels 
           232 . 1  Right rear wheels 
           232 . 2  Left rear wheels 
           234 . 1 ,  234 . 2 ,  234 . 3 , 
           234 . 4  Signal lines 
           236  Combined module 
           238 . 1 ,  238 . 2  Control lines 
           240  Second compressed air supply 
           242 . 1 ,  242 . 2  Spring-type actuator 
           244 . 1 ,  244 . 2  Double-acting brake cylinders 
           246  Parking brake switch 
           248  Electronic switch 
           250  Third compressed air supply 
         BV Braking specification 
         ECU Electronic control unit 
         EPH Holding brake unit 
         pB Brake pressure 
         pBH Rear axle brake pressure 
         pBV Front axle brake pressure 
         pF 1 , pF 2  Holding brake pressures 
         pG 1 , pG 2 , pG 3  Limit pressures 
         pR Redundancy pressure 
         pSV Front axle control pressure 
         pS 1  First control pressure 
         pU Ambient pressure 
         pV Supply pressure 
         pVS Pilot control pressure 
         SD Pressure signal 
         SD 2  Second pressure signal 
         SV 1 , SV 2 , SV 3 , SV 4 , 
         SV 5 , SV 6 , SV 7  First to seventh valve control signal 
         S 1 . 1 , S 1 . 2  Control signals 
         S 2  Electronic holding signal 
         S 3 . 1 , S 3 . 2  ABS signals 
         TCV Trailer control unit