METHOD FOR OPERATING A BRAKING SYSTEM OF A COMMERCIAL VEHICLE

Description

[0001] The invention relates to a method for operating a braking system of a commercial vehicle, in particular an agricultural or municipal commercial vehicle, wherein the braking system has a service braking system, an auxiliary braking system and braking devices for vehicle wheels of the commercial vehicle, wherein in the service braking system, in normal operation, upon actuation of at least one brake actuating device, at least one associated service brake actuator is controlled, via which, upon actuation, an actuation of the respectively associated braking device corresponding to the actuation of the at least one brake actuating device is carried out, wherein in the auxiliary braking system, an actuation of at least one of the braking devices can be initiated via at least one control unit, and wherein, upon detection of an at least partial failure of the service braking system, an emergency operation is carried out.Furthermore, the invention relates to a control unit, a braking system of a commercial vehicle and a commercial vehicle.

[0002] Braking systems in motor vehicles typically include a service brake system to brake the vehicle wheels, and thus the motor vehicle as well, while the vehicle is moving by actuating one or more associated brake actuation devices. Furthermore, a braking system typically includes an auxiliary braking system, which can hold at least individual vehicle wheels in their current position when the vehicle is stationary, for example when parked, by applying the brakes. A braking system in a motor vehicle should be implemented as a redundant system to ensure that the vehicle can still be braked, if possible, even if part of the braking system fails.In some cases, the auxiliary braking system is specifically used in the event of at least a partial failure of the service braking system in order to be able to brake the vehicle.

[0003] US 2005 / 0168064 A1 discloses a braking system for a commercial vehicle, which is a towing vehicle, such as a semi-trailer truck. The braking system comprises a service braking system and an auxiliary braking system, via which the wheels of the commercial vehicle can be braked independently of one another via braking devices. The braking system of US 2005 / 0168064 A1 is implemented as an electronic braking system in which, on the one hand, an actuation of a brake actuation device of the service braking system in the form of a brake pedal and, on the other hand, an actuation of a parking brake actuation device of a parking braking system in the form of a handbrake lever are each detected by control units and converted into corresponding control of brake actuators in a data bus system.Brake actuators of a front axle of the commercial vehicle and brake actuators of a rear axle of the commercial vehicle are integrated in separate circuits.

[0004] In the event of a partial failure of the service brake system due to a failure of the front axle brake circuit, the front axle wheels are then braked by another means during emergency operation. In one variant, actuation of the parking brake actuation device in the auxiliary brake system during emergency operation is converted into braking of the front axle wheels via the brake actuators. A control unit actuates a valve, thereby supplying the front axle brake actuators with fluid from a circuit for a commercial vehicle trailer that is independent of the front axle brake circuit.

[0005] DE 10 2019 219 407 A1 relates to a braking system for a motor vehicle. In particular, this is an integrated braking system. An integrated braking system is a structural unit that combines a multitude of functions in a compact design. In particular, such an integrated braking system comprises a master cylinder that can be actuated using a brake pedal, an additional pressure source, in particular a plunger arrangement that is designed to be electromechanically actuated, a braking circuit that connects the hydraulic components to one another, control valves that are used to control the brakes, a control unit for controlling the control valves, and / or a fluid reservoir that provides a supply of fluid. The integrated braking system comprises at least some, preferably all, of the aforementioned components.The control valves and the control unit, in conjunction with the pressure source, control the brakes and, preferably, provide corresponding driving and braking assistance functions. These driving and braking assistance functions are used, among other things, for autonomous or semi-autonomous driving, as well as during heavy braking.

[0006] DE 10 2019 211 537 A1 relates to a hydraulic braking system for a motor vehicle, having at least two brake circuits, each having at least one hydraulically actuated wheel brake and each having at least one electrically operable pressure generator, wherein the pressure generators can be controlled depending on a braking request of the motor vehicle or a driver of the motor vehicle.

[0007] Based on the prior art described above, it is the object of the present invention to provide a braking system for a commercial vehicle by means of which, in the event of an at least partial failure of a service braking system, the commercial vehicle can nevertheless be reliably braked, while at the same time enabling a simple construction of this braking system.

[0008] From a process engineering perspective, this problem is solved based on the preamble of claim 1 in conjunction with its characterizing features. From a device engineering perspective, the problem is solved by the technical features of claim 7, which relates to a [device / system]. The dependent claims that follow thereon each represent advantageous developments of the invention. Furthermore, claims 8 to 11 relate to a braking system for a commercial vehicle, in which an aforementioned control unit is provided. Finally, claim 12 also relates to a commercial vehicle with an aforementioned braking system.

[0009] According to the independent claim 1, in a method for operating a braking system comprising a service braking system, an auxiliary braking system, and braking devices for vehicle wheels of the commercial vehicle, in the service braking system, during normal operation, upon actuation of at least one brake actuation device, at least one associated service brake actuator is activated, via which an actuation of the respective associated braking device is carried out, corresponding to the actuation of the at least one brake actuation device. Furthermore, in the auxiliary braking system, actuation of at least one of the braking devices can be initiated via at least one control unit. If an at least partial failure of the service braking system is detected, an emergency operation is also carried out.

[0010] The method according to the invention is applied to a braking system of a commercial vehicle, which is in particular an agricultural or municipal commercial vehicle. The commercial vehicle is particularly preferably an agricultural tractor. The commercial vehicle preferably has several axles in the form of a front axle and a rear axle, of which at least one axle is equipped with brakeable vehicle wheels. However, it is particularly preferred that all vehicle wheels of the vehicle can be braked, for which purpose a braking device is assigned to each vehicle wheel. Within the meaning of the invention, a braking device for a vehicle wheel is in particular a disc brake, which can be designed as a wet multi-disc brake.

[0011] Within the scope of the invention, each braking device is preferably assigned to a service brake actuator, via which an actuation of the associated braking device is carried out when triggered. This actuation takes place during normal operation of the braking system when an actuation takes place at at least one brake actuation device of the service brake system, wherein the intensity of an actuation of the respective braking device via the associated service brake actuator depends on the intensity of the actuation of the at least one brake actuation device. Within the meaning of the invention, the at least one brake actuation device is in particular a brake pedal, which can be actuated by a driver of the commercial vehicle to brake the commercial vehicle via the service brake system.

[0012] Within the scope of the invention, the braking system can be provided with exactly one brake actuation device, the actuation of which, during normal operation of the braking system, controls all service brake actuators of the service brake system, and accordingly, the vehicle wheels are also braked via the associated braking devices. However, two brake actuation devices are particularly preferably provided in order to be able to replicate the function of a steering brake via the service brake system.Thus, by actuating one brake actuating device, only the service brake actuator(s) are activated, which actuate the braking devices located on one side of the commercial vehicle in the longitudinal direction of the commercial vehicle, while actuating the other brake actuating device results in the braking devices located on the other side of the commercial vehicle being actuated by actuating the service brake actuator(s) located there.

[0013] The auxiliary braking system in the braking system is provided to brake the vehicle in accordance with the driver's instructions in the event of an at least partial failure of the service braking system. According to the invention, the auxiliary braking system is also designed to implement a parking brake function of the commercial vehicle during normal operation of the braking system, in response to a corresponding instruction from the driver, in order to hold the commercial vehicle in a current position by braking the vehicle wheels. In the present case, in the method according to the invention for operating the braking system, this parking brake function is implemented by initiating actuation of at least one of the braking devices of the vehicle wheels via the at least one control unit.Particularly preferably, the at least one control unit initiates this actuation within the scope of the parking brake function when a corresponding command has been given by a vehicle driver to an actuating device. In particular, this actuating device is a device for which a continuously variable command can be given by the vehicle driver, such as a brake lever.

[0014] Within the scope of the method according to the invention, emergency operation of the braking system is performed if at least a partial failure of the service braking system is detected. If it is detected that the service braking system of the braking system is not functioning properly, in particular because pressure is not being built up in the braking system or is only building up to an insufficient degree, emergency operation is initiated. According to the invention, this is preferably performed at a level of failure of the service braking system at which inadequate braking of the commercial vehicle is to be feared.

[0015] The invention now comprises the technical teaching that, in the auxiliary braking system, the actuation of the at least one braking device is initiated via the at least one control unit by controlling at least one auxiliary brake actuator. During emergency operation, the at least one control unit accesses the auxiliary brake actuator upon detection of the actuation of the at least one brake actuation device, wherein the at least one control unit uses the auxiliary brake actuator to adjust the actuation of the at least one braking device based on the degree of actuation of the at least one brake actuation device.

[0016] In other words, in the auxiliary braking system of the braking system, the at least one braking device is actuated by the at least one control unit controlling at least one auxiliary brake actuator. During emergency operation, the at least one control unit also controls the auxiliary brake actuator if actuation of the at least one brake actuation device of the service braking system has been detected, i.e., if the driver has given an instruction to brake the commercial vehicle.However, since this request cannot be implemented via the service brake system or can only be implemented to an insufficient extent due to the at least partial failure of the service brake system, the at least one control unit now controls the auxiliary brake actuator in such a way that the actuation of the at least one braking device via the auxiliary brake actuator is modeled on the intensity of the actuation of the at least one brake actuation device of the service brake system.

[0017] Such a method for operating a braking system has the advantage that even in the event of an at least partial failure of the service braking system of the braking system, at least approximately sufficient braking of the commercial vehicle can still be achieved via the auxiliary braking system. Thus, in the event of a failure of the service braking system, a driver is still able to brake the commercial vehicle so that they can bring the commercial vehicle to a standstill. This occurs automatically and without any additional action by the driver, in that the at least one control unit, in emergency mode, automatically performs a corresponding actuation of the at least one braking device by accessing the auxiliary braking actuator upon detection of the actuation of the at least one braking actuation device.Since the auxiliary brake actuator is controlled via the at least one control unit, a simpler brake system design can be realized. This allows for electronic actuation of the at least one auxiliary brake actuator of the auxiliary brake system, thus largely eliminating the need for hydraulic / pneumatic components.

[0018] According to the invention, the auxiliary brake system can brake the same vehicle wheels that can also be braked by the service brake system by means of the one or more auxiliary brake actuators. In this respect, the at least one auxiliary brake actuator within the auxiliary brake system has access, in particular, to the same braking devices. Particularly preferably, two associated braking devices for vehicle wheels of a vehicle axle are actuated via an auxiliary brake actuator when controlled by the at least one control unit.

[0019] In US 2005 / 0168064 A1, the braking devices in the auxiliary braking system are also actuated via a control unit of the auxiliary braking system, in which this control unit electronically controls the brake actuators. However, in emergency mode, the brake actuators are not automatically actuated via the control unit according to the specifications on the brake pedal. Instead, in a variant of US 2005 / 0168064 A1, the brake actuators on the front axle of the commercial vehicle are supplied from a brake circuit for a trailer of the commercial vehicle according to the specifications on the handbrake lever of the parking brake. Furthermore, the same brake actuators are assigned to the auxiliary braking system and the service braking system.

[0020] According to the invention, in the method according to the invention for operating a braking system, the actuation of the at least one auxiliary brake actuator is initiated via the at least one control unit, preferably by electronic access of the control unit to the auxiliary brake actuator, wherein the at least one control unit can, within the scope of the invention, access the at least one auxiliary brake actuator directly electronically, or actuation and thus access can take place via intermediate components, for example further control units and / or electronic components. The auxiliary brake actuator particularly preferably also functions as a parking brake actuator, i.e. the brake actuator of the auxiliary braking system is also used to apply the brakes to the vehicle as part of a parking brake function. In particular, the auxiliary brake actuator comprises a spring-loaded cylinder.

[0021] The fact that, during emergency operation, the actuation of the at least one braking device is "oriented" to a degree of actuation of the at least one brake actuation device via the at least one control unit means, within the meaning of the invention, that such an actuation of the at least one braking device is initiated via the auxiliary brake actuator via the at least one control unit that corresponds as closely as possible to a specification of the at least one brake actuation device of the service brake system. Within the scope of the method according to the invention, an attempt is therefore made via the control unit during emergency operation to compensate for the at least partial failure of the service brake system as far as possible and to implement the driver's specifications for the at least one brake actuation device with regard to braking the commercial vehicle as far as possible.Particularly preferably, an actuation of the at least one braking device is carried out via the at least one control unit by means of the auxiliary brake actuator, which corresponds to the specification on the at least one brake actuation device.

[0022] Within the scope of the method according to the invention, a corresponding warning message is preferably issued upon detection of the at least partial failure of the service brake system and thus upon commencement of emergency operation, in order to alert the driver of the commercial vehicle to the at least partial failure of the service brake system. This warning message can be provided as a visual and / or acoustic warning message.

[0023] According to one embodiment of the invention, during emergency operation, a required braking torque is determined based on the degree of actuation of the at least one brake actuation device, wherein the required braking torque is subsequently used to adjust the control of the at least one auxiliary brake actuator. During emergency operation, the braking torque to be set at the braking devices is determined based on the vehicle driver's input to the at least one brake actuation device. This required braking torque is then subsequently used to adjust the control of the at least one auxiliary brake actuator in order to at least substantially generate the required braking torque at the associated braking devices via the at least one auxiliary brake actuator.Particularly preferably, the determination of the required braking torque is also carried out by the at least one control unit, wherein the at least one control unit is provided with information about the degree of actuation of the at least one brake actuation device. In particular, for this purpose, the at least one control unit exchanges data with a sensor system that detects the degree of actuation of the at least one brake actuation device.

[0024] According to one possible embodiment of the invention, an at least partial failure is detected as an at least insufficient pressure supply to the at least one associated service brake actuator via a pressure source to which the at least one associated service brake actuator is connected upon detection of the actuation of the at least one brake actuation device. Thus, if it is detected that there is no pressure supply or that the pressure supply to the respective service brake actuator in the service brake system is too low to provide a required braking torque, emergency operation is initiated, and actuation is thus carried out automatically by means of the auxiliary brake actuator via the at least one control unit.For this purpose, the at least one associated service brake actuator and the pressure source are preferably integrated into a brake circuit of the service brake system, whereby, depending on the type of actuator, this can be a hydraulic or pneumatic brake circuit in which the actuator can be supplied with hydraulic fluid or with compressed air.

[0025] In a further development of the aforementioned design option, the at least insufficient pressure supply in the service brake system is detected by a sensor, which is preferably a pressure sensor. This provides a simple way to determine whether the pressure supply is too low.

[0026] In one embodiment of the invention, the control of the at least one auxiliary brake actuator is initiated via a first control unit, which is in particular a brake control unit. For this purpose, data is transmitted in a data transmission system between the first control unit and a second control unit, wherein the second control unit may be a transmission control unit. The auxiliary brake actuator is then controlled via the second control unit in accordance with a specification from the first control unit. Advantageously, this allows the at least one auxiliary brake actuator to be indirectly controlled via the first control unit by communication with the second control unit, which then implements the specifications from the first control unit by directly controlling the auxiliary brake actuator.

[0027] In a further development of the invention, in the auxiliary brake system, actuation of the at least one braking device is carried out by depressurizing a fluid cylinder in each of the at least one auxiliary brake actuators, which is equipped with an actuating piston preloaded into an actuating position. Thus, actuation of the at least one braking device via the at least one auxiliary brake actuator is carried out when the respective fluid cylinder of the auxiliary brake actuator is depressurized. For this purpose, the respective fluid cylinder is designed as an inverse fluid cylinder.

[0028] For this purpose, the actuating piston of the fluid cylinder is preloaded into an actuating position. The actuating piston is moved into an open position by supplying fluid to the fluid cylinder, in which position the actuation of the at least one braking device via the auxiliary brake actuator is canceled. Accordingly, when the respective fluid cylinder of the auxiliary brake actuator is supplied with fluid, actuation of the at least one braking device is reduced or even canceled depending on the pressure. If no fluid is supplied and the associated pressure relief is reduced, the actuation of the at least one braking device via the auxiliary brake actuator is performed due to the preload of the actuating piston.

[0029] Particularly preferably, the auxiliary brake system also provides at least one valve, via which a pressure supplying each fluid cylinder of the at least one auxiliary brake actuator can be adjusted. This is necessary within the scope of the invention in order to also adjust the actuation of the at least one braking device via the auxiliary brake actuator by controlling the pressure. This is because, to implement emergency operation, a controlled actuation of the at least one braking device via the auxiliary brake actuator is necessary. Thus, a proportional valve or a combination of several valves can be provided for adjusting the pressure.

[0030] The invention further relates to a control unit which, in an auxiliary braking system of a braking system of a commercial vehicle, is configured to initiate control of at least one auxiliary brake actuator for actuating at least one braking device of each vehicle wheel. Furthermore, the control unit is configured to initiate emergency operation upon detection of an at least partial failure of a service braking system of the braking system, to access the at least one auxiliary brake actuator during the emergency operation upon detection of actuation of at least one brake actuation device of the service braking system, and to initiate, via the auxiliary brake actuator, an actuation of the at least one braking device oriented towards a degree of actuation of the at least one brake actuation device.

[0031] Such a design of a control unit and its use in a braking system of a commercial vehicle has the advantage that, in the event of an at least partial failure of the service braking system of the braking system, the control unit can independently access the at least one auxiliary brake actuator of the auxiliary braking system in order to subsequently bring about braking by actuating at least one braking device via the auxiliary brake actuator, which braking is oriented towards a command from a vehicle driver via at least one brake actuation device. This can also be achieved with a compact design through direct or indirect electronic access of the control unit to the at least one auxiliary brake actuator. The control unit is in particular a brake control unit of the braking system.

[0032] Furthermore, the control device according to the invention is then preferably designed such that a method for operating a braking system according to one or more of the variants described above can be implemented.

[0033] An aforementioned control unit is preferably part of a braking system for a commercial vehicle, wherein this braking system comprises a service braking system, an auxiliary braking system, braking devices for vehicle wheels of the commercial vehicle, and at least the control unit according to the invention. The service braking system has at least one brake actuation device, via which, when actuated in normal operation, at least one associated service brake actuator can be controlled, wherein the at least one associated service brake actuator, when actuated in normal operation, actuates the respectively assigned braking device corresponding to the actuation of the at least one brake actuation device. Furthermore, the auxiliary braking system has an auxiliary brake actuator which can be actuated via the control unit and, when actuated, actuates at least one of the braking devices.

[0034] As described above, in the event of an at least partial failure of the service brake system, the control unit according to the invention then accesses the auxiliary brake actuator upon detecting the actuation of the at least one brake actuation device and, via the auxiliary brake actuator, actuates the at least one brake device based on the degree of actuation of the at least one brake actuation device. Thus, a reliable braking system for a commercial vehicle can be realized in which, even in the event of an at least partial failure of the service brake system, the commercial vehicle can be braked in response to a driver's command via the control unit and thus without any active action by the driver. The braking system of the commercial vehicle can be operated in the manners described above within the scope of the method according to the invention.

[0035] The aforementioned braking system includes a first control unit and a second control unit, which are connected to one another in a data transmission system, preferably a CAN bus. While the first control unit is a brake control unit, the second control unit is a transmission control unit of a transmission located in the area of ​​an axle of the commercial vehicle. The second control unit can control the auxiliary brake actuator. The transmission control unit is particularly implemented when the auxiliary brake actuator is located in the area of ​​the transmission or even integrated into it.

[0036] In a further development of a braking system, the auxiliary brake actuator comprises a fluid cylinder with an actuating piston that is preloaded into an actuating position. The actuating piston can be moved into an open position by supplying fluid to the fluid cylinder under pressure, in which position the actuation of the at least one braking device via the auxiliary brake actuator is canceled. Accordingly, the fluid cylinder of the respective auxiliary brake actuator is designed as an inverse fluid cylinder in that, when pressure is supplied, actuation of the at least one braking device is reduced or canceled via the fluid cylinder depending on a pressure, whereas the fluid cylinder causes actuation of the at least one braking device when there is no pressure supply.

[0037] In the service brake system of the braking system, the at least one associated service brake actuator is arranged in each brake circuit, in which, during normal operation of the braking system, the respective associated service brake actuator is controlled depending on the actuation of the at least one brake actuation device. Preferably, each brake circuit is designed as a hydraulic circuit in which fluid is provided in the form of hydraulic fluid. The service brake actuators are then configured as hydraulic actuators. Alternatively, the fluid of the brake circuit can also be compressed air, in which case the components and the service brake actuators in the brake circuit are provided as pneumatic components.

[0038] In addition, a valve plate can be provided in the brake circuit, via which, during normal operation of the brake system, an actuation of the at least one brake actuation device is converted into corresponding pressures for controlling the service brake actuators by means of corresponding valves.

[0039] Alternatively, but preferably in addition to the aforementioned variant, a sensor system can be provided in at least one brake circuit in which the service brake actuators are controllable, via which sensor system a fluid pressure of the at least one brake circuit can be monitored. This sensor system can be used to determine the at least partial failure of the service brake system if the service brake actuators are not supplied or are supplied only insufficiently. Particularly preferably, the sensor system is formed by a pressure sensor, by means of which a fluid pressure in the at least one brake circuit can be determined. Such a pressure sensor can be provided on a valve block of the at least one brake circuit.

[0040] The invention also relates to a commercial vehicle in which a braking system according to one or more of the aforementioned variants is provided. The commercial vehicle is preferably an agricultural or municipal vehicle, and in particular an agricultural tractor.

[0041] The invention is not limited to the specified combination of the independent claims or those dependent thereon. Furthermore, possibilities arise for combining individual features, even if they emerge from the claims, the following description of a preferred embodiment of the invention, or directly from the drawings. The reference of the claims to the drawings by the use of reference symbols is not intended to limit the scope of protection of the claims.

[0042] An advantageous embodiment of the invention, which is explained below, is illustrated in the drawings. It shows: Fig. 1 is a schematic view of a braking system of a commercial vehicle, according to a preferred embodiment of the invention; Fig. 2 is a representation of the braking system of Fig. 1 , shown in normal operation and in a first actuation state; Fig. 3 a representation of the braking system from Fig. 1 , shown in normal operation and in a second operating state; and Fig. 4 a representation of the braking system from Fig. 1 , shown in an emergency operation.

[0043] Out of Fig. 11 shows a schematic view of a braking system 1 of a commercial vehicle, which is in particular an agricultural vehicle in the form of a farm tractor. The braking system 1 is designed according to a preferred embodiment of the invention and serves to brake vehicle wheels 2 and 3 of a vehicle axle 4 of the commercial vehicle, which in the present case is a rear axle of the commercial vehicle. Within the scope of the invention, however, an additional vehicle axle, in particular a front axle of the commercial vehicle, with brakeable vehicle wheels can also be provided within the braking system 1, wherein this additional vehicle axle can be equipped in an analogous manner with a braking system for braking the vehicle wheels.

[0044] Each of the vehicle wheels 2 and 3 is assigned a braking device 5 or 6 by the braking system 1, with the braking devices 5 and 6 in the present case being designed as disc brakes. Specifically, the disc brakes can be wet multi-disc brakes. When actuated, the individual braking device 5 or 6 ensures that the corresponding vehicle wheel 2 or 3 is decelerated or stalled.

[0045] The braking system 1 according to the invention comprises a control unit 7 in the form of a brake control unit and a service brake system 8. Within the service brake system 8, two service brake actuators 9 and 10 with hydraulic fluid cylinders are provided, wherein the service brake actuator 9 actuates the braking device 5 when pressure is applied, and the service brake actuator 10 actuates the braking device 6 when pressure is applied. In this case, in a manner known in principle to those skilled in the art, when the respective fluid cylinder of the service brake actuator 9 or 10 is supplied with hydraulic fluid, a displacement of a respective piston is caused, which is coupled to the respective associated braking device 5 or 6, respectively. This is preferably realized via a respective ball ramp. Accordingly, when the piston of the respective fluid cylinder is displaced, an actuation of the respective associated braking device 5 or 6 is represented due to the coupling.

[0046] The service brake actuators 9 and 10 are integrated into a hydraulic brake circuit 11 by being connected to a valve block 14 via lines 12 and 13. Also connected to this valve block 14 in the brake circuit 11 are a pressure source 15 in the form of a hydraulic pump of the commercial vehicle, a tank 16 for hydraulic fluid, a pressure accumulator 17, a pressure sensor 18, and two additional lines 19 and 20. The pressure sensor 18 can be used to determine the hydraulic fluid reservoir pressure prevailing in the brake circuit 11.

[0047] In this case, a brake actuation device 21 and 22, respectively, is connected to lines 19 and 20, with the brake actuation devices 21 and 22 each being present as brake pedals, via which a driver of the commercial vehicle can actuate the service brake actuators 9 and 10 of the service brake system 8. The degree of actuation of the respective brake actuation device 21 and 22 is detected by sensors and determined by the control unit 7. The control unit 7 also detects the pressure in the brake circuit 11, determined by the pressure sensor 18.

[0048] As in Fig. 1As can be seen, the control unit 7 is connected to two further control units 24 and 25 in a data transmission system in the form of a CAN bus 23, of which the control unit 24 is a vehicle control unit and the control unit 25 is a transmission control unit of a transmission 26. The transmission 26 is located in the area of ​​the vehicle axle 4.

[0049] Of the control units 24 and 25, control unit 24 is connected to an actuating device 27 of an auxiliary braking system 28, wherein this actuating device 27 is present in the form of a brake lever. The actuating position of this brake lever is detected via the control unit 24. The auxiliary braking system 28 is provided within the braking system 1 during normal operation to implement a parking brake function for locking the two vehicle wheels 2 and 3 in order to hold the commercial vehicle in a current position. This locking occurs during normal operation of the braking system 1 upon corresponding instruction from the vehicle driver via the actuating device 27.

[0050] For this purpose, the auxiliary brake system 28 is assigned an auxiliary brake actuator 29, which in this case is integrated into the transmission 26 in the area of ​​the vehicle axle 4. This auxiliary brake actuator 29 comprises a fluid cylinder 30, in which an actuating piston is preloaded via a spring element into an actuating position, in which position the actuating piston acts on the two braking devices 5 and 6 via a bridge 31 and actuates them. The fluid cylinder 30 is supplied with hydraulic fluid from a pressure source 32 of the transmission 26 inversely to an actuation of the actuating device 27, so that in normal operation, when the actuating device 27 is released, pressurization of the fluid cylinder 30 and thus a movement of the actuating piston counter to the spring element is initiated, whereby actuation of the braking devices 5 and 6 via the auxiliary brake actuator 29 is canceled.If, however, the actuating device 27 is actuated by the vehicle driver, the pressure in the fluid cylinder 30 is progressively relieved, and thus, due to the action of the spring element via the actuating piston of the fluid cylinder 30, an increasing actuation of the braking devices 5 and 6 is also brought about. In order to be able to adjust the degree of actuation, at least one valve—not shown here—is assigned to the auxiliary brake actuator 29, with this at least one valve being controlled by the control unit 25. The required degree of actuation is communicated to the control unit 25 within the CAN bus 23 by the control unit 24.

[0051] In the Fig. 2 to 4 are different states of the braking system 1 from Fig. 1 shown, whereby only the components currently actively participating in a braking process are shown. Fig. 2a state of the braking system 1 when the service brake is used, wherein the brake actuation devices 21 and 22 are actuated by a vehicle driver. In this case, an actuation of the individual brake actuation devices 21 or 22 is converted at the valve block 14 into a setting of a corresponding pressure in the lines 12 and 13. The service brake actuators 9 and 10 subsequently actuate the two brake devices 5 and 6, so that the vehicle wheels 2 and 3 are braked accordingly. In this case, the vehicle driver can also actuate the brake actuation devices 21 and 22 differently, or just one of the brake actuation devices 21 or 22, in order to implement the function of a steering brake of the commercial vehicle by a one-sided stronger or only one-sided actuation and via one of the brake devices 9 or 10.

[0052] Out of Fig. 3A further state of the brake system 1 emerges, where Fig. 3 The situation is shown in which the actuating device 27 is actuated by the vehicle driver and the auxiliary braking system 28 is operated as a parking brake. The respective degree of actuation of the actuating device 27 is detected by the control unit 24 and transmitted via the CAN bus 23 to the control unit 25, which then controls the auxiliary brake actuator 29 in order to actuate the braking devices 5 and 6 via the bridge 31 via the auxiliary brake actuator 29 in a manner corresponding to the degree of actuation of the actuating device 27. As the degree of actuation of the actuating device 27 increases, the control unit 25 initiates an increasing pressure relief of the fluid cylinder 30.

[0053] Finally, Fig. 4the state of the braking system 1 in emergency operation due to at least a partial failure of the service braking system 8. The reason for the failure of the service braking system 8 could be a failure of the pressure source 15, leaks in the area of ​​the lines 12 and 13, or even a failure of one or both service braking actuators 9 and 10. In particular, the first two reasons for failure are detected by the control unit 7 using the pressure sensor 18, with the control unit 7 then initiating emergency operation upon detecting an excessively low fluid pressure in the brake circuit 11. This is preferably also indicated to the driver visually by means of a warning lamp and / or acoustically via a warning signal.

[0054] As a special feature, when the brake actuation devices 21 and 22 are actuated, the control unit 7 then independently ensures that the braking of the vehicle wheels 2 and 3 specified by the driver at the brake actuation devices 21 and 22 is brought about. For this purpose, the control unit 7 initiates an actuation of the auxiliary brake actuator 29 via the control unit 25 by means of the CAN bus 23, whereby an actuation of the brake devices 5 and 6 is implemented via the auxiliary brake actuator 29 in accordance with the driver's specification at the brake actuation devices 21 and 22. The control unit 7 detects the degree of actuation of the brake actuation devices 21 and 22, whereby the control unit 7, by means of the control unit 25, brings about an increasing pressure relief of the fluid cylinder 30 of the auxiliary brake actuator 29 with increasing degree.Ultimately, in emergency operation, a braking command from the driver on the brake actuation devices 21 and 22 is automatically converted by means of the auxiliary braking system 28 into a required braking of the vehicle wheels 2 and 3 of the vehicle axle 4.

[0055] This means that in the event of only a partial pressure failure in the service brake system 8, the braking request is automatically calculated in such a way that only a missing difference to the driver's request is fed via the auxiliary brake system 28.

[0056] The braking force applied via the auxiliary brake system 28 is mechanically added to the forces generated by the residual pressure in the service brake system 8 via the service brake actuators 9 and 10. This occurs automatically and dynamically. Even if the pressure in the service brake system 8 continues to drop during braking, the compensating braking demand to the auxiliary brake system 28 is automatically adjusted. In the event of a complete loss of pressure in the service brake system 8, this control system ensures that the driver's braking request is transmitted 100% to the auxiliary brake system 28.

[0057] By means of a method according to the invention for operating a braking system, reliable braking of a commercial vehicle can still be achieved with a compact design in the event of at least a partial failure of a service braking system. Reference symbol

[0058] 1 Brake system 2 Vehicle wheel 3 Vehicle wheel 4 Vehicle axle 5 Brake device 6 Brake device 7 Control unit 8 Service brake system 9 Service brake actuator 10 Service brake actuator 11 Brake circuit 12 Line 13 Line 14 Valve block 15 Pressure source 16 Tank 17 Pressure accumulator 18 Pressure sensor 19 Line 20 Line 21 Brake actuation device 22 Brake actuation device 23 CAN bus 24 Control unit 25 Control unit 26 Transmission 27 Actuation device 28 Auxiliary brake system 29 Auxiliary brake actuator 30 Fluid cylinder 31 Bridge 32 Pressure source

Claims

1. Method for operating a brake system (1) of a commercial vehicle, wherein the brake system (1) comprises a service brake system (8), a brake control unit (7), an auxiliary brake system (28) and brake devices (5, 6) for vehicle wheels (2, 3) of a vehicle axle (4) of the commercial vehicle, wherein the vehicle axle (4) is a rear axle of the commercial vehicle, wherein, in the case of the service brake system (8), at least one associated service brake actuator (9, 10) is actuated in normal operation when at least one brake actuating device (21, 22) is actuated, via which service brake actuator with actuation an actuation, corresponding to the actuation of the at least one brake actuating device (21, 22), of the respective associated brake device (5, 6) is carried out, wherein the auxiliary brake system (28) is provided in normal operation for the generation of a parking brake function, wherein, in the auxiliary brake system (28), an actuation of at least one of the brake devices (5, 6) can be initiated via at least one transmission control unit (25), and wherein emergency operation is carried out when an at least partial failure of the service brake system (8) is detected in the form of a failure of a pressure source (15) of the service brake system (8), leaks in the area of lines (12, 13) or a failure of one or both service brake actuators (9, 10), characterized in that, in the auxiliary brake system (28), the actuation of the at least one brake device (5, 6) is initiated via the transmission control unit (25) by actuating at least one auxiliary brake actuator (29), in that, in the course of emergency operation, the auxiliary brake actuator (29) is accessed by the brake control unit (7) with detection of the actuation of the at least one brake actuating device (21, 22), and in that an adjustment of an actuation of the at least one brake device (5, 6) oriented to a degree of the actuation of the at least one brake actuating device (21, 22) is carried out by the brake control unit (7) by means of the auxiliary brake actuator (29), wherein the auxiliary brake actuator (29) and the service brake actuators (9, 10) act on the same brake device (5, 6).

2. Method according to Claim 1, characterized in that, in the course of emergency operation, a required brake torque is determined based on the degree of the actuation of the at least one brake actuating device (21, 22), wherein the required brake torque is subsequently used for the setting of the actuation of the at least one auxiliary brake actuator (29).

3. Method according to Claim 1 or 2, characterized in that, as an at least partial failure, an at least too low pressure supply of the at least one associated service brake actuator (9, 10) via a pressure source (15) is detected, to which pressure source the at least one associated service brake actuator (9, 10) is connected when the actuation of the at least one brake actuating device (21, 22) is detected.

4. Method according to Claim 3, characterized in that the at least too low pressure supply in the service brake system (8) is detected via a pressure sensor (18).

5. Method according to one of the preceding claims, characterized in that the actuation of the at least one auxiliary brake actuator (29) is initiated via the brake control unit (7), to which end a data transmission is carried out in a data transmission system between the brake control unit (7) and the transmission control unit (25), wherein the actuation of the auxiliary brake actuator (29) is carried out via the transmission control unit (25) according to a specification of the first brake control unit (7).

6. Method according to one of the preceding claims, characterized in that, in the auxiliary brake system (28), an actuation of the at least one brake device (5, 6) is carried out by, in the case of the at least one auxiliary brake actuator (29), a fluid cylinder (30) in each case being depressurized, which is equipped with an actuating piston preloaded into an actuating position.

7. Brake control unit (7) which is designed to initiate, in an auxiliary brake system (28) of a brake system (1) of a commercial vehicle, an actuation of at least one auxiliary brake actuator (29) for the actuation of at least one brake device (5, 6) of in each case one vehicle wheel (2, 3), wherein the brake control unit (7) is further designed to initiate emergency operation when an at least partial failure of a service brake system (8) of the brake system (1) is detected, to access the at least one auxiliary brake actuator (29) in the course of emergency operation upon detection of an actuation of at least one brake actuating device (21, 22) of the service brake system (8) via a transmission control unit (25), and in the process to initiate an actuation of the at least one brake device (5, 6) oriented to a degree of an actuation of the at least one brake actuating device (21, 22) via the auxiliary brake actuator (29).

8. Brake system (1) for a commercial vehicle, comprising a service brake system (8), an auxiliary brake system (28), brake devices (5, 6) for vehicle wheels of a vehicle axle (4) of the commercial vehicle, wherein the vehicle axle (4) is a rear axle of the commercial vehicle, and a brake control unit (7), a vehicle control unit (24) and a transmission control unit (25), wherein the service brake system (8) has at least one brake actuating device (21, 22), via which in each case at least one associated service brake actuator (9, 10) can be actuated upon actuation in normal operation, wherein the at least one associated service brake actuator (9, 10), upon actuation in normal operation, performs an actuation of the respective associated brake device (5, 6) which corresponds to the actuation of the at least one brake actuating device (21, 22), characterized in that the brake control unit (7) is connected in a data transmission system to the transmission control unit (25), and the auxiliary brake system (28) has an auxiliary brake actuator (29), wherein the auxiliary brake actuator (29) and the service brake actuators (9, 10) act on the same brake device (5, 6), wherein the auxiliary brake actuator (29) can be actuated in normal operation via the transmission control unit (25) and, in emergency operation, an actuation of the auxiliary brake actuator (29) can be initiated by the brake control unit (7) via the transmission control unit (25) in order to brake the vehicle wheels (2, 3).

9. Brake system (1) according to Claim 8, characterized in that the auxiliary brake actuator (29) has a fluid cylinder (30) with an actuating piston which is preloaded into an actuating position, wherein the actuating piston can be transferred into an open position by the pressurized supply of the fluid cylinder (30) with fluid, in which open position the actuation of the at least one brake device (5, 6) via the auxiliary brake actuator (29) is cancelled.

10. Brake system (1) according to one of Claims 8 and 9, characterized in that, in the service brake system (8), the at least one associated service brake actuator (9, 10) is arranged in in each case one brake circuit (11), in which, in normal operation, control of the in each case corresponding service brake actuator (9, 10) takes place in a manner dependent on the actuation of the at least one brake actuating device (21, 22).

11. Brake system (1) according to one of Claims 8 to 10, characterized in that, in the service brake system (8), a sensor system is provided in at least one brake circuit (11), in which the service brake actuators (9, 10) are controllable, via which sensor system a pressure of fluid of the at least one brake circuit (11) can be monitored.

12. Commercial vehicle comprising a brake system (1) according to one of Claims 8 to 11.