BRAKING SYSTEM FOR A MOTOR VEHICLE

Description

[0001] The invention relates to a braking system for a motor vehicle.

[0002] From DE 10 2020 121 082 A1, an electronically controlled, pressure-medium-operated secondary braking system for a commercial vehicle is known. The secondary braking system comprises spring-applied brake cylinders and an electronically controlled brake control valve, by means of which the braking force of the spring-applied brake cylinders can be reduced by supplying pressure medium and increased by draining pressure medium. Furthermore, the secondary braking system includes an electronic brake control unit for controlling the brake control valve depending on the current value of a braking signal. A pressure medium inlet of the brake control valve is connected to a pressure medium source via a supply line, a pressure medium outlet of the brake control valve to a pressure medium sink, and a working port of the brake control valve to the spring-applied brake cylinders via a working line.In addition, a 3 / 2-way solenoid valve and a check valve blocking flow towards the brake control valve are arranged in the working line.

[0003] Furthermore, according to DE 10 2020 121 082 A1, a control input of the check valve can be alternately connected to the hydraulic fluid source or a pressureless hydraulic reservoir via the 3 / 2-way solenoid valve, so that the check valve is open / closed towards the brake control valve when the 3 / 2-way solenoid valve is energized / de-energized. A hand pump is connected to the working line via a pressure line, which allows hydraulic oil to be manually pumped from a pressureless hydraulic reservoir into the spring brake cylinders in the event of a defect in the 3 / 2-way solenoid valve. No redundancy is provided for the 3 / 2-way solenoid valve, so if it opens unintentionally, the spring brake cylinders are vented via the check valve and the brake control valve. The EP 3 536 570 B1, on the other hand, has redundancy in the form of a control valve and a redundancy valve for a parking brake module.This increases safety in the event of electrical failures, but still requires a mechanical interface in the cabin to release pressure from the spring brake cylinders.

[0004] To create redundancy, solutions using bistable valves and redundant control units are also known. Bistable valves typically remain in one position in the event of an electrical or mechanical failure. This means that an emergency function is not possible if the parking brake is accidentally engaged. Even with this solution, the driver still needs a mechanical interface to manually release the pressure if the parking brake is accidentally deactivated. Redundant control units require additional costs for a second control unit and software development. This solution only makes sense if two control units are already in use in the vehicle.

[0005] An object of the present invention is to provide a braking system with reduced hardware and software complexity. The braking system should ensure that a parking lock can be activated in the event of an unintentionally jammed valve. This object is achieved by the subject matter of independent claim 1. Advantageous embodiments are the subject of the dependent claims, the following description, and the figures. The present invention provides a braking system for a motor vehicle. The braking system comprises a first directional control valve designed as a control valve, a second directional control valve designed as a redundancy valve, and a third directional control valve designed as a brake valve. The braking system also includes a brake cylinder. The invention is described below primarily in connection with a brake cylinder.These statements also apply analogously to multiple such brake cylinders, which can be connected in parallel to the brake valve. The brake cylinder, or its piston rod, is mechanically connected to a parking lock. In alternative configurations, the brake system does not have a second-way valve designed as a redundancy valve. Furthermore, the brake system includes a pressure medium source. The pressure medium source (e.g., a tank or accumulator) is designed to dispense a pressure medium. When the vehicle's ignition is switched on, a drive motor of the vehicle can fill the pressure medium source. The pressure medium can be pneumatic (e.g., compressed air) or hydraulic (e.g., oil). Thus, the brake system can also be either pneumatic or hydraulic.Furthermore, the braking system includes an electronic control unit, a parking lock, and a pressureless reservoir. The parking lock is designed to lock at least one wheel of the vehicle when and as long as the parking lock is activated. In particular, a mechanical parking lock can lock the at least one wheel of the vehicle, wherein the mechanical parking lock is pre-tensioned by a parking lock spring such that the parking lock is activated. The piston of the brake cylinder can release the pre-tension of the parking lock spring, thus deactivating the parking lock function. For this to occur, a deactivation pressure must be built up within the brake cylinder.

[0006] When the parking lock is to be released during normal operation, particularly when the electronic control unit is active, both the control valve and the redundancy valve are activated and thus in the open position. The control valve and the redundancy valve then supply the brake valve with pressure and hydraulic fluid, respectively. The brake valve is typically a normally open proportional valve (pressure reduction upon activation), specifically a 3 / 3-way valve. The brake valve is not activated, meaning it transmits pressure to the brake cylinder when in the open position. The pressure status can be monitored via a pressure sensor. Pressure builds up within the brake cylinder until, in the case of a spring-applied brake, it is fully released. The control valve and the redundancy valve remain permanently active as long as the parking lock is released, i.e., while driving.In this sense, the brake system according to the invention is designed such that the control valve and the redundancy valve are mechanically biased in a closed state, whereas the brake valve is mechanically biased in an open state. The electronic control unit is configured to control the control valve and the redundancy valve such that they move into an open state against the mechanical bias. This allows hydraulic fluid to be directed from the hydraulic fluid source, via the control valve and the redundancy valve, and downstream via the brake valve, which is mechanically biased in the open state, into the brake cylinder. The hydraulic fluid builds up a deactivation pressure in the brake cylinder, thus disengaging the parking lock.

[0007] In the event of a mechanical defect in the control valve or the redundancy valve, resulting in a jammed open position of the affected valve, the pressure in the brake cylinder cannot be released through the jammed valve when the parking brake is applied. As long as the ignition is switched on or the electronic control unit for the individual devices is powered, this pressure in the brake cylinder can be released by opening the brake valve, overcoming the constant pressure supply through the defective valve.In this sense, the electronic control unit of the brake system according to the invention is configured to control the brake valve in such a way that it enters a closed state, so that pressure medium flows from the brake cylinder directly into the unpressurized tank via the brake valve and no pressure medium is directed into the brake cylinder via the control valve or via the redundancy valve and the brake valve if the control valve or the redundancy valve remains in the open state due to a mechanical defect, although it should be in the closed state.

[0008] If the electronic control unit were to be switched off, the brake valve would also be deactivated, which would repressurize the brake cylinder and release the parking brake. To avoid such a risky situation, a mechanism, implemented primarily through software, is in place that alternately opens and closes the brake valve. When the vehicle's ignition is switched off, so that the engine is no longer running to power the vehicle, the brake cylinder chamber is alternately filled, pressurized, and vented. This empties the pressure source (tank or reservoir) that supplies the parking brake system until a defined pressure threshold, such as the deactivation pressure, is no longer reached within the brake cylinder.In this sense, one embodiment provides that the electronic control unit is configured to control the brake valve such that it alternately moves between the open and closed states when the vehicle's ignition is switched off. This causes the brake cylinder to be alternately filled and emptied until the pressure medium source is sufficiently depleted that the pressure within the brake cylinder no longer reaches a defined limit during filling. The electronic control unit is specifically configured to switch itself off when the pressure within the brake cylinder no longer reaches the limit during filling.

[0009] While the brake cylinder is pressurized, a pressure sensor can detect a sufficiently low pressure level in the accumulator. Once a specific threshold is reached, ensuring the vehicle comes to a safe stop, the electronic control unit can be switched off. In a further embodiment, the brake system also includes a pressure sensor configured to measure the line pressure within a line connecting the brake valve to the brake cylinder. The processor unit is configured to access the line pressure measured by the pressure sensor and switch itself off if the line pressure falls below the predetermined limit during the brake cylinder filling process.

[0010] According to a further embodiment, the brake system also includes an electronic locking unit, wherein the control valve is forced into the closed position by mechanical preload when the electronic control unit is in an inactive state, so that no hydraulic fluid is directed from the hydraulic fluid source via the control valve towards the brake valve. Accordingly, no hydraulic fluid is directed via the control valve and the brake valve into the brake cylinder to build up the deactivation pressure, thus disabling the parking lock.

[0011] The characteristic "inactive state" can be understood to mean, in particular, that the electronic control unit can no longer control the control valve, the redundancy valve, and the brake valve. Specifically, the electronic control unit no longer controls the energizing of the electromagnets of the control valve, redundancy valve, and brake valve when it is in the inactive state. The electronic control unit is in an inactive state, in particular, when it fails due to a fault. Conversely, the characteristic "active state" can be understood to mean that the electronic control unit controls the control valve, the redundancy valve, and the brake valve.In particular, the electronic control unit controls the current flow to the electromagnets of the control valve, redundancy valve, and brake valve when the electronic control unit is in an active state. The electronic control unit is considered to be in an active state when the vehicle's ignition is switched on and no fault occurs during its operation that would lead to its failure.

[0012] When the electronic control unit is inactive, the electronic locking unit is configured to control the redundancy valve in such a way that the redundancy valve opens. This allows hydraulic fluid from the hydraulic fluid source to flow through the redundancy valve and the mechanically pre-tensioned brake valve (which is open) into the brake cylinder, building up the deactivation pressure in the brake cylinder and thus disengaging the parking lock. This prevents unintentional activation of the parking brake function without the need for two control units, while simultaneously ensuring a correct response in the event of a failure of the electronic control unit. Furthermore, in the event of a failure of the central electronic control unit, the braking system allows the driver to activate the parking lock without an additional mechanical interface.

[0013] The electronic locking unit is specifically designed to store a normal operating control signal, which contains the last valid operating state of the control valve before the electronic control unit became inactive. The last valid operating state of the control valve specifically indicates that the control valve is in the open position. When the control valve is open, hydraulic fluid from the hydraulic fluid source is directed through the control valve and the brake valve into the brake cylinder, building up the deactivation pressure and thus disengaging the parking lock.Furthermore, the electronic locking unit can be configured, when the electronic control unit is inactive, to control the redundancy valve based on the normal operating control signal, such that the redundancy valve is opened. When the redundancy valve is open, hydraulic fluid from the hydraulic fluid source is directed through the redundancy valve and the brake valve into the brake cylinder, building up the deactivation pressure and thus disengaging the parking lock.

[0014] The driver can bring the vehicle to a standstill if the electronic control unit fails by applying the service brake. The driver can then engage the parking lock from the driver's seat by switching off the vehicle's ignition. The function of the electronic locking unit may be dependent on the ignition status, whereby the electronic locking unit can check whether current is flowing through a corresponding pin ("TRM15") on the vehicle's main electronic control unit. If the electronic locking unit detects that the vehicle's ignition is off, it can deactivate the redundancy valve, causing it to enter a closed state.When the redundancy valve is in the closed position, pressure escapes from the brake cylinder via the deactivated brake valve back to the now deactivated redundancy valve and into a pressureless reservoir. In a further embodiment, the locking unit—when the electronic control unit is inactive and the vehicle's ignition is switched off—is configured to control the redundancy valve in such a way that the redundancy valve is closed, preventing any pressure medium from the pressure medium source from flowing through the redundancy valve towards the brake valve. Instead, pressure medium from the at least one brake cylinder is released via the brake valve and the redundancy valve into the pressureless reservoir, thus reducing the deactivation pressure within the at least one brake cylinder and activating the parking lock.

[0015] The redundancy valve is specifically designed as a proportional valve. The speed of the parking brake activation can be limited by intentionally restricting the flow from the redundancy valve to the tank. This prevents potential misuse by the driver, such as performing an ignition cycle while driving, for example, when a red warning light is illuminated. In a further embodiment, the electronic locking unit is configured to control the redundancy valve in such a way that when the redundancy valve is closed, the flow of pressurized fluid released into the unpressurized tank via the redundancy valve is restricted.

[0016] To enable the effect of a secondary brake, the brake valve can be controlled such that the pressure is reduced to the required level to achieve the desired secondary braking force. The secondary brake can be released by increasing the pressure again, thereby deactivating the brake valve. The control valve and the redundancy valve are active during the application of the secondary brake but do not participate in this function. In a further embodiment, the electronic control unit is configured to open the control valve and the redundancy valve.Furthermore, the electronic control unit is configured to control the brake valve in such a way that sufficient hydraulic fluid, which has been routed from the hydraulic fluid source via the control valve and the redundancy valve to the brake valve, reaches the brake cylinder via the brake valve and builds up a secondary brake pressure there, causing the parking lock to generate the intended secondary braking force. The electronic control unit is also configured to close the brake valve when the secondary braking force is no longer required.

[0017] When the parking lock is to be operated or activated during normal operation, i.e., when the electronic control unit is in an active state, the control valve and the redundancy valve are deactivated, i.e., closed, so that the brake cylinder can be vented via the deactivated brake valve. When the brake valve is deactivated, it is in the open state, allowing hydraulic fluid to flow from the brake cylinder through the brake valve, the control valve, and the redundancy valve into the depressurized reservoir. In a further embodiment, the electronic control unit is configured to control the control valve and the redundancy valve in such a way that they close.Furthermore, the electronic control unit is designed to open the brake valve when the electronic control unit is in the active state. This releases hydraulic fluid from the brake cylinder, via the brake valve, the control valve, and the redundancy valve, into the depressurized reservoir, thus reducing the deactivation pressure within the brake cylinder and activating the parking lock.

[0018] If the control valve and the redundancy valve exhibit a low flow rate, the rate of brake cylinder emptying can be increased by simultaneously activating the brake valve, i.e., by closing the brake valve. The brake valve then vents the brake cylinder directly into the depressurized reservoir, bypassing the control valve and the redundancy valve. In this situation, the control valve and the redundancy valve only release the hydraulic fluid on its way from the control valve and the redundancy valve, respectively, to the brake valve, which occurs very quickly.In this sense, according to a further embodiment, the electronic control unit is designed to put the brake valve into the closed state, whereby pressure medium is released from the brake cylinder via the brake valve directly into the unpressurized tank, so that the deactivation pressure within the at least one brake cylinder is reduced and the parking lock is activated.

[0019] In the following, exemplary embodiments of the invention are explained in more detail with reference to the schematic drawing, wherein identical or similar elements are provided with the same reference numeral. Here, Fig. 1 a top view of part of a braking system for a motor vehicle and a trailer, Fig. 2 an enlarged view of part of the braking system according to Fig. 1 and Fig. 3 exemplary state variables of the braking system according to Fig. 1 .

[0020] Fig. 1 Figure 1 shows part of a braking system 1 for a motor vehicle 2 (not shown in detail). The motor vehicle 2 is, for example, an agricultural vehicle, in particular a tractor. The braking system 1 fulfills, in particular, a parking brake function for the wheels 13 of the motor vehicle 2 and optionally a [missing information - likely a specific function]. Fig. 1 The trailer brake 3 of a trailer 4 is only indicated. The functions described in more detail below can be part of a tractor braking system platform, the so-called EBP platform. The EBP platform is intended to ensure the safe operation of the braking system 1 under various failure scenarios.

[0021] The braking system 1 includes an electronically controlled parking brake module 5, details of which are given in Fig. 2 The parking brake module 5 comprises a first 3 / 2-way valve designed as a control valve 6, a second 3 / 2-way valve designed as a redundancy valve 7, a pressure-controlled changeover valve 8, and a 3 / 3-proportional directional control valve designed as a brake valve 10. The parking brake module 5 is supplied with hydraulic fluid via a supply line 11 from a pressure source 9, in the illustrated embodiment with hydraulic pressure fluid. The control valve 6 and the redundancy valve 7 are each connected to the pressure source 9 via the supply line 11 in a parallel hydraulic circuit. The term "connected" means, in particular, that the connected elements are hydraulically or pneumatically connected to each other, i.e., that a pressure medium, e.g., air or a hydraulic fluid, especially oil, can flow from one element to the other and, if necessary,vice versa.

[0022] In the illustrated embodiment, the control valve 6 and the redundancy valve 7 are identical parts, although this is not mandatory. A valve spool 12 of the control valve 6 and the redundancy valve 7 are each located in a valve housing (not shown) by a spring element 34.1, 34.2 in a configuration formed by Fig. 2 The closed switching position shown is pre-tensioned ("normally closed"), which corresponds to a closed state of the control valve 6 and the redundancy valve 7. When the control valve 6 and the redundancy valve 7 are in the closed state, no hydraulic fluid from the hydraulic fluid source 9 is directed through the control valve 6 and the redundancy valve 7 towards the changeover valve 8, the brake valve 10 located further downstream, and a brake cylinder 14. The valve spools 12 of the control valve 6 and the redundancy valve 7 can be moved from the closed switching position to an open switching position, which corresponds to an open state of the control valve 6 and the redundancy valve 7, by energizing a first electromagnet EM1. The energizing of the first electromagnet EM1 is carried out by an electronic control unit 16.When the control valve 6 and the redundancy valve 7 are in the open state, pressure medium from the pressure medium source 9 is directed via the control valve 6 and the redundancy valve 7 and can be directed via the changeover valve 8 and the brake valve 10 located further downstream into the brake cylinder 14.

[0023] On the output side, the control valve 6 and the redundancy valve 7 are each connected to an input 8.1, 8.2 of the changeover valve 8, so that the higher pressure of each of the two valves 6, 7 is output via an output 8.3 of the changeover valve 8 to supply pressure fluid to two spring-loaded brake cylinders 14, each assigned to a wheel 13, via the brake valve 10. Optionally, the trailer brake 3 can also be supplied with pressure. If the control valve 6 fails, the pressure of the redundancy valve 7 can still be used, provided the redundancy valve 7 is functioning. A pressure sensor 15 measures the pressure output via the brake valve 10 and transmits the measured pressure to the electronic control unit 16 of the brake system 1.

[0024] The brake valve 10 comprises a valve housing 21, a valve spool 22, a spring element 23, and a second electromagnet EM2. The valve spool 22 of the brake valve 10 is held within the valve housing 21 by the spring element 23 in a manner Fig. 2 The open switch position shown is pre-tensioned ("normally open"), which corresponds to an open state of the brake valve 10. When the brake valve 10 is in the open state, hydraulic fluid, which has been supplied from the hydraulic fluid source 9 via the open control valve 6 and the open redundancy valve 7, as well as the changeover valve 8, is supplied via the brake valve 10 to the brake cylinder 14. Inside the brake cylinder 14, the hydraulic fluid builds up a deactivation pressure, thus deactivating a parking lock 24. Fig. 2 shows only one of the two brake cylinders 14 after Fig. 1 . However, the statements relating to the description of the figures apply analogously to both brake cylinders 14, which are connected to the brake valve 10 in a hydraulic parallel circuit.

[0025] A piston rod 25 of the brake cylinder 14 is mechanically connected to the parking lock 24. The piston rod 25 of the brake cylinder 14 is mechanically pre-tensioned by a spring element 26 such that the parking lock 24 is activated, thereby locking the wheels 13. The deactivation pressure counteracts the pre-tension provided by the spring element 26 and moves the piston rod 25 such that the parking lock 24 is deactivated, thereby releasing the wheels 13. The electronic control unit 16 can control the energization of the second electromagnet EM2 of the brake valve 10 such that the valve spool 22 of the brake valve 10 is moved from the open switching position, through a neutral position, to an open switching position, which corresponds to a closed state of the brake valve 10.When the brake valve 10 is in the closed state, pressure fluid from the brake cylinder 14 can flow via the brake valve 10 into a pressureless tank T, thus reducing the deactivation pressure and activating the parking lock 24.

[0026] If at least one of the valve spools 12 of the two valves 6, 7 is in its open switching position, then a specified pressure can be routed through the control valve 6 and / or the redundancy valve 7 and discharged through the changeover valve 8. The spring-loaded brake cylinders 14 and the trailer brake 3 can then be actuated via the open brake valve 10 such that the parking lock 24 is released against the spring preload. The wheels 13 of the motor vehicle 2 and / or the trailer 4 are then not locked. If, on the other hand, both valve spools of the two valves 6, 7 are in their closed switching position, then no pressure is routed through the control valve 6 and the redundancy valve 7 and discharged through the changeover valve 8 and the open brake valve 10. The spring-loaded brake cylinders 14 and the trailer brake 3 are then not pressurized as described above, but are instead discharged.The wheels 13 of the motor vehicle 2 and / or the trailer 4 are then locked. In this context, it can be said that the valve arrangement 5 has an inverting switching characteristic. The parking lock 24 of the motor vehicle 2 and the trailer brake 3 are engaged when no pressure is output via the brake valve 10, and released when a sufficiently high pressure is output via the brake valve 10, resulting in the deactivation pressure within the brake cylinder 14 or in the trailer brake 3.

[0027] Fig. 1 Figure 1 shows that the electronic control unit 16 of the brake system 1 can be connected to an electronic (main) control unit 18 of the motor vehicle 2 via a CAN bus 17. In the illustrated embodiment, the electronic (main) control unit 18 of the motor vehicle 2 is connected, in particular, to a human-machine interface 19. Using the human-machine interface 19, a driver or user of the motor vehicle 2 can operate the at least one brake cylinder 14 of the motor vehicle 2 and / or the trailer brake 3 of the trailer 4.

[0028] When the parking lock 24 is to be operated or activated during normal operation, i.e., when the electronic control unit 16 is in an active state, the control valve 6 and the redundancy valve 7 are deactivated, i.e., placed in the closed position, so that the brake cylinder 14 can be vented via the deactivated brake valve 10. When the brake valve 10 is deactivated, it is in the open position, so that hydraulic fluid from the brake cylinder 14 flows via the brake valve 10, the changeover valve 8, the control valve 6, and the redundancy valve 7 into the unpressurized tank T.

[0029] If the control valve 6 and the redundancy valve 7 have a low flow rate, the rate of emptying the brake cylinder 14 can be increased by simultaneously activating the brake valve 10, i.e., by closing the brake valve 10. The brake valve 10 then vents the brake cylinder 14 directly into the unpressurized tank T, thus bypassing the control valve 6 and the redundancy valve 7. In this situation, the control valve 6 and the redundancy valve 7 only release the hydraulic fluid on its way from the control valve 6 and the redundancy valve 7, respectively, to the brake valve 10, which happens very quickly.

[0030] To enable the effect of a secondary brake, the electronic control unit 16 controls the brake valve 10 such that the pressure prevailing in the brake cylinder 14 is reduced to the level required to achieve the desired braking force. The secondary brake can be released by increasing the pressure again, by which the electronic control unit 16 deactivates the brake valve. The control valve 6 and the redundancy valve 7 are active during the application of the secondary brake but do not participate in this function.

[0031] It is possible that the control valve 6 and / or the redundancy valve 7 may have a mechanical defect, resulting in the affected valve 6 and / or 7 becoming stuck in the open position. In this case, the pressure within the brake cylinder 14 cannot be released via the stuck valve 6 and / or 7 when the parking lock 24 is actuated. As long as the ignition of the vehicle 2 is switched on or the electronic control unit 16 for controlling the individual devices is powered, this pressure within the brake cylinder 14 can be released by opening the brake valve 10, overcoming the constant supply through the defective valve 6 and / or 7. The electronic control unit 16 will energize the second electromagnet EM2 of the brake valve 10 in such a way that its valve spool 22 is moved into the closed position.When the valve spool 22 is in the closed position, the brake cylinder 14 is connected to the unpressurized tank T via the brake valve 10, while the control valve 6 and the redundancy valve 7 are disconnected from the brake cylinder 14. As a result, hydraulic fluid flows from the brake cylinder 14 directly into the unpressurized tank T of the brake system 1 via the brake valve 10. Furthermore, no hydraulic fluid from the hydraulic fluid source 9 is directed into the brake cylinder 14 via the control valve 6 or redundancy valve 7, the changeover valve 8, and the brake valve 10.

[0032] If the electronic control unit 16 is also to be switched off, then the second electromagnet EM2 of the brake valve 10 would normally no longer be energized. This would cause the brake valve 10 to enter the pre-tensioned state, i.e., the valve spool 22 would be forced by the spring 23 into the position indicated by Fig. 2 The open switch position shown would be shifted. This would repressurize the brake cylinder 14 and release the parking brake 24. To avoid such a risky situation, the electronic control unit 16 (before it switches itself off or is allowed to be switched off) alternately moves the brake valve 10 between the open and closed states. This occurs when the ignition of the vehicle 2 is switched off, so that the engine no longer runs to power the vehicle 1 and the pressure source is no longer being filled. This causes the brake cylinder 14 to be alternately filled, pressurized, and vented, so that the pressure source 9, which supplies the brake cylinder 14, is emptied to such an extent that the deactivation pressure is no longer reached within the brake cylinder 14 during its filling process.

[0033] Fig. 3 The scenario described above is illustrated by time-dependent changes in state values. For example, a graph in Fig. 3 The first graph shown below, 28, depicts the time course of the state of the control valve 6. Another one in Fig. 3 The second graph 29 shown below depicts the time course of the state of the redundancy valve 7. Above the first and second graphs 28, 29, a third graph 30 shows the time course of the state of the brake valve 10. Above the third graph 30, a fourth graph 31 shows the time course of the relative pressure (0% corresponds to a pressureless state, 100% to the maximum permissible pressure) prevailing within the brake cylinder 14. A pressure limit 32 is also indicated. If the pressure prevailing within the brake cylinder 14 is below the limit 32, then the parking lock 24 is activated. The limit 32 could, for example, be the deactivation pressure described above. Alternatively, a lower value can be chosen to increase safety against unintended deactivation of the parking lock 24.Above the fourth graph 31, a fifth graph 32 shows the time course of an output print of the printing source 9.

[0034] At a first time point t1, the vehicle 2 is stopped, e.g., by means of a service brake. The control valve 6, the redundancy valve 7, and the brake valve 10 remain in their open state, so that a pressure above the limit value 32 continues to exist within the brake cylinder 14, thus keeping the parking lock 24 deactivated. At a subsequent second time point t2, the activation of the parking lock 24 is initiated, e.g., by the driver operating the human-machine interface 19 accordingly. From the second time point t2, the redundancy valve 7 is moved from the open switching position to the closed switching position by its spring element 34.2. However, this does not work for the control valve 6 because a mechanical defect prevents the spring element 34.1 of the control valve 6 from moving its valve spool 12 to the closed position. The control valve 6 therefore remains in the open state.The brake valve 10 remains in its intended open state. The pressure 31 inside the brake cylinder 14 does not decrease because the control valve 6 remains open, so hydraulic fluid from the hydraulic fluid source 9 continues to flow unintentionally into the brake cylinder 14 via the control valve 6, the changeover valve 8, and the brake valve 10.

[0035] At a subsequent third time point t3, the electronic control unit 16 detects that the control valve 6 is in the open state, although it should be in the closed state to activate the parking lock 24. To nevertheless enable activation of the parking lock 24, the electronic control unit 16 energizes the second electromagnet EM2 of the brake valve 10 such that its valve spool 22 moves into the closed switching position. As a result, hydraulic fluid flows from the brake cylinder 14 via the brake valve 10 directly into the unpressurized tank T. This causes the pressure 31 within the pressure cylinder 14 to drop below the limit value 32, and the parking lock 24 is activated.

[0036] At a subsequent fourth time point t4, the ignition of the motor vehicle 2 is switched off, so that the pressure medium source 9 is no longer filled and can be emptied. The electronic control unit 16 now energizes the second electromagnet EM2 of the brake valve 10 such that its valve spool 22 moves alternately between the open and closed switching positions. This causes pressure medium from the emptying pressure medium source 9 to flow into the brake cylinder 14 via the still-open control valve 6, the changeover valve 8, and the brake valve 10, thus building up pressure in the brake cylinder 14. This pressure is then released again in a closing cycle 36 following the opening cycle 35 (in which the brake valve is closed). Fig. 3 It is evident that during a first opening cycle 35 of the brake valve 10 the limit value 32 is still exceeded, but during the following opening cycles 35 it is no longer exceeded.

[0037] As soon as the electronic control unit 16 detects that the limit value 32 is no longer reached during an opening cycle of the brake valve 10, it can switch itself off at a fifth time t 5. In the by Fig. 3 In the illustrated embodiment, the electronic control unit 16 waits for one further opening cycle before initiating its shutdown. When the electronic control unit 16 is switched off, it is in an inactive state, so the brake valve 10 is returned to its mechanically pre-tensioned open state. The redundancy valve 7 remains in its mechanically pre-tensioned closed state. The control valve 6 remains in its jammed open state. However, insufficient hydraulic fluid is now supplied from the at least partially emptied hydraulic fluid source 9 via the control valve 6, the changeover valve 8, and the brake valve 10 to the brake cylinder 14 to build up the deactivation pressure in the brake cylinder 14 and deactivate the parking lock 24. To detect the pressure within the brake cylinder 14, the brake system 1 in the illustrated embodiment includes a pressure sensor 15.The pressure sensor 15 measures the line pressure within a brake cylinder line 37, which connects the brake valve 10 to the brake cylinder 14. The processor unit 16 accesses the line pressure measured by the pressure sensor 15 and can switch off as described above if the line pressure no longer reaches the specified limit value during the filling of the brake cylinder 14 (i.e., during one of the opening cycles 35 described above).

[0038] It is essential to prevent the pressure supply to the brake cylinder 14 and the trailer brake 3 from failing while the motor vehicle 2 and the trailer 4 are in motion, thus preventing the wheels 13 of the motor vehicle 2 or the trailer 4 from locking up. This pressure supply function is controlled during normal operation of the brake system 1 by the electronic control unit 16 of the brake system 1. For this purpose, the electronic control unit 16 of the brake system 1 is connected to the control valve 6 and the redundancy valve 7 via electronic control lines 20. When the electronic control unit 16 of the brake system 1 energizes the first electromagnets EM1 of the control valve 6 and the redundancy valve 7 via the electronic control lines 20, the valve spools 12 of the control valve 6 and the redundancy valve 7 are moved from the closed position to the open position against the spring preload.

[0039] However, if the electronic control unit 16 of the brake system 1 does not function properly in a faulty operation (inactive state of the electronic control unit 16), then this function is controlled by an electronic locking unit 26, which is described in more detail below and is shown in the embodiment below. Fig. 1 The control valve 6 is integrated into the electronic control unit 16. Due to mechanical preload, the control valve 6 closes when the electronic control unit 16 is in the inactive state. Thus, no pressure medium is directed from the pressure medium source 16 through the control valve towards the brake valve 24. Consequently, no pressure medium is directed through the control valve 6 and the brake valve 7 into the brake cylinder 14 to build up the deactivation pressure and thus deactivate the parking lock 24. To counteract this, when the electronic control unit 16 is in the inactive state, the electronic locking unit 26 controls the redundancy valve 7, opening it to the open state.This directs pressure medium from the pressure medium source 9 via the redundancy valve 7 and the brake valve 10, which is mechanically pre-tensioned in the open state, into the brake cylinder 14, building up the deactivation pressure in the brake cylinder 14 so that the parking lock 24 is deactivated.

[0040] To implement this functionality, the electronic interlocking unit 26 stores a normal operating control signal 38. This normal operating control signal 38 contains or describes a last valid operating state of the control valve 6 before the electronic control unit 16 became inactive. The last valid operating state of the control valve 6 specifically includes the information that the control valve 6 is in the open position. When the electronic control unit 16 is in the inactive state, the electronic interlocking unit 26 controls the first electromagnet EM1 of the redundancy valve 7 based on the normal operating control signal 38 such that the valve spool 12 of the redundancy valve 7 is moved into the open position.When the redundancy valve 7 is in the open state, pressure medium from the pressure medium source 9 is directed via the redundancy valve 7, the changeover valve 8 and the brake valve 10, which is mechanically pre-tensioned in the open state, into the brake cylinder 14, building up the deactivation pressure there, so that the parking lock 24 is deactivated.

[0041] If the electronic control unit 16 fails, the driver can bring the vehicle 2 to a standstill by applying the service brake. The driver can then engage the parking lock 24 from the driver's seat by switching off the ignition of the vehicle 2. The function of the electronic locking unit 26 may depend on the ignition status, whereby the electronic locking unit 26 can check whether current is flowing through a corresponding pin ("TRM15") on the electronic control unit 18 of the vehicle 2. If the electronic locking unit 26 detects that the ignition of the vehicle 2 is switched off, it can deactivate the redundancy valve 7, causing the redundancy valve 7 to enter the closed state.When the redundancy valve 7 is in the closed position, pressure escapes from the brake cylinder 14 via the brake valve 10, which is pre-tensioned in the open position, back to the now deactivated redundancy valve 7 and into the unpressurized reservoir T. The activation speed of the parking lock 24 can be limited by intentionally restricting the flow from the redundancy valve 7, which is designed as a proportional valve, to the unpressurized reservoir T. This can be achieved by the electronic locking unit 26 energizing the electromagnet EM1 of the redundancy valve 7 accordingly. In this way, potential misuse by the driver, who might initiate an ignition cycle while driving with a red warning light illuminated, can be prevented. Bezugszeichen

[0042] A1 Pressure medium source connection A2 Tank connection A3 Brake cylinder connection EM1 Electromagnet control valve / redundancy valve EM2 Electromagnet brake valve t 1 first time point t 2 second time point t 3 third time point t 4 fourth time point t 5 fifth time point T unpressurized tank 1 Braking system 2 Motor vehicle 3 Trailer brake 4 Trailer 5 Parking brake module 6 Control valve 7 Redundancy valve 8 Changeover valve 8.1 First inlet changeover valve 8.2 Second inlet changeover valve 8.3 Changeover valve outlet 9 Pressure medium source 10 Brake valve 11 Supply line 12 Valve spool 13 Wheel 14 Brake cylinder 15 Pressure sensor 16 Electronic control unit of the brake system 17 CAN bus 18 Electronic control unit of the motor vehicle 19 Human-machine interface 20 Electronic control line 21 Valve housing 22 Valve spool 23 Spring element 24 Parking lock 25 Piston rod 26 Electronic locking unit 27 Spring element 28 Time course of the control valve state 29 Time course of the redundancy valve state 30 Time course of the Condition of the brake valve 31 Time course brake cylinder pressure 32 Limit pressure 33 Time course output pressure Pressure medium source 34.1 Spring element control valve 34.2 Spring element redundancy valve 35 Opening cycle 36 Closing cycle 37 Brake cylinder line 38 Normal operation control signal.

Claims

1. Brake system (1) for a motor vehicle (2), the braking system (1) comprising - a first directional valve designed as a control valve (6), - a second directional valve designed as a redundancy valve (7), - a third directional valve designed as a brake valve (10), - a brake cylinder (14), - a pressure medium source (9), - an electronic control unit (16), - a parking lock (24), and - a pressureless tank (T), wherein - the control valve (6) and the redundancy valve (7) are mechanically preloaded in a closed state, - the brake valve (10) is mechanically preloaded in an open state, and - the electronic control unit (16) is configured - to control the control valve (6) and the redundancy valve (7) in such a way that they move into an open state, counter to the mechanical preload, whereby pressure medium from the pressure medium source (9) is directed via the control valve (6) and the redundancy valve (7) as well as downstream via the brake valve (10), which is mechanically preloaded in the open state, into the brake cylinder (14) and builds up a deactivation pressure in the brake cylinder (14) such that the parking lock (24) is deactivated, and - to control the brake valve (10) in such a way that it moves into a closed state, such that pressure medium from the brake cylinder (14) flows directly into the pressureless tank (T) via the brake valve (10) and no pressure medium is directed via the control valve (6) or the redundancy valve (7) as well as the brake valve (10) into the brake cylinder (14) if the control valve (6) or the redundancy valve (7) remains in the open state due to a mechanical defect, although it should be in the closed state.

2. Brake system (1) according to Claim 1, wherein, when an ignition of the motor vehicle (2) is switched off, the electronic control unit (16) is configured to control the brake valve (10) in such a way that it alternately moves into the open state and into the closed state, such that the brake cylinder (14) is alternately filled and emptied, until the pressure medium source (9) is emptied in such a way that the pressure inside the brake cylinder (14) no longer reaches a specified limit value pressure (32) during its filling.

3. Brake system (1) according to Claim 2, wherein the electronic control unit (16) is configured to switch off when the pressure inside the brake cylinder (14) no longer reaches the limit value pressure (32) during its filling.

4. Brake system (1) according to Claim 2 or 3, the brake system (1) further comprising a pressure sensor (15), wherein - the pressure sensor (15) is configured to measure a line pressure within a line (37) connecting the brake valve (10) to the brake cylinder (14), and - the processor unit (16) is configured to access the line pressure measured by the pressure sensor (15) and to switch off when the line pressure no longer reaches the specified limit value (32) during the filling (35) of the brake cylinder (14).

5. Brake system (1) according to any one of the preceding claims, the brake system (1) further comprising an electronic locking unit (26), wherein - the control valve (6) is moved into the closed state by the mechanical preload when the electronic control unit (16) is in an inactive state, such that no pressure medium from the pressure medium source (9) is directed via the control valve (6) in the direction of the brake valve (10), and - the electronic locking unit (26), when the electronic control unit (16) is in the inactive state, is configured to control the redundancy valve (7) in such a way that the redundancy valve (7) is moved into the open state, whereby pressure medium from the pressure medium source (9) is directed via the redundancy valve (7) and the brake valve (10), which is mechanically preloaded in the open state, into the brake cylinder (14) and builds up the deactivation pressure in the brake cylinder (14), such that the parking lock (24) is deactivated.

6. Brake system (1) according to Claim 5, wherein the electronic locking unit (26) is configured - to store a normal operation control signal (38) containing a last valid operating state of the control valve (6) before the state of the electronic control unit (16) has become inactive, and - to control the redundancy valve (7), when the electronic control unit (16) is in the inactive state, based on the normal operation control signal (38) in such a way that the redundancy valve (7) is moved into the open state.

7. Brake system (1) according to either of the preceding Claims, 5 or 6, wherein the locking unit (26) is configured to control the redundancy valve (7) in such a way that the redundancy valve (7) is moved into the closed state when the electronic control unit (16) is in the inactive state and when the ignition of the motor vehicle (2) is switched off, such that no pressure medium from the pressure medium source (9) is directed via the redundancy valve (7) in the direction of the brake valve (14), but rather pressure medium is discharged from the at least one brake cylinder (14) via the brake valve (10) and the redundancy valve (7) into the pressureless tank (T), such that the deactivation pressure within the at least one brake cylinder (14) is released and the parking lock (24) is activated.

8. Brake system (1) according to Claim 7, wherein the electronic locking unit (26) is configured to control the redundancy valve (7) in such a way that a volume flow of pressure medium, which is discharged via the redundancy valve (7) into the pressureless tank (T), is restricted when the redundancy valve (7) is moved into the closed state.

9. Brake system (1) according to any one of the preceding claims, wherein the electronic control unit (16) is configured - to move the control valve (6) and the redundancy valve (7) into the open state, and - to control the brake valve (10) in such a way that sufficient pressure medium, which has been directed from the pressure medium source (9) via the control valve (6) and the redundancy valve (7) to the brake valve (10), enters the brake cylinder (14) via the brake valve (10) and builds up a secondary brake pressure there, which leads to the parking lock (24) generating a provided secondary braking force, and - to move the brake valve (10) into the closed state if the secondary braking force is no longer to be generated.

10. Brake system (1) according to any one of the preceding claims, wherein the electronic control unit (16) is configured - to control the control valve (6) and the redundancy valve (7) in such a way that they are moved into the closed state, and - to move the brake valve (10) into the open state when the electronic control unit (16) is in the active state, whereby pressure medium from the brake cylinder (14) is discharged via the brake valve (10) and via the control valve (6) and the redundancy valve (7) into the pressureless tank (T), such that the deactivation pressure inside the brake cylinder (14) is released and the parking lock (24) is activated.