Method, device, and computer program for determining a holding power of a parking brake unit

Abstract

The invention relates to a method for determining a holding power of a parking brake unit (10) of a vehicle combination (1) with an operating brake unit (60). The method comprises the following steps: a) providing (S1) an actual holding force (25); b) when the vehicle combination (1) is at a standstill, determining (S2) a minimum target holding force (35), wherein determining the minimum target holding force (35) comprises: b1) reducing (S2.1) the actual holding force (25), detecting and storing actual holding force values (45); b2) if a vehicle movement (55) is registered, increasing (S2.2) the actual holding force (25); b3) determining (S2.3) the target holding force (35) from at least one stored actual holding force value (45) and a safety margin (S); and b4) setting (S2.4) the actual holding force (25) to a value which corresponds at least to the determined minimum target holding force (35); c) comparing (S3) the determined minimum target holding force (25) with a threshold holding force (65) of the parking brake unit (10); and d) determining (S4) the holding power (75) of the parking brake unit (10). The invention further relates to a computer program for carrying out the method and to a device for determining a holding power.

Description

[0001] METHOD, DEVICE AND COMPUTER PROGRAM FOR DETERMINING THE HOLDING CAPACITY OF A PARKING BRAKE UNIT

[0002] The present invention relates to a method for determining the holding capacity of a parking brake of a vehicle combination, the vehicle combination comprising a towing vehicle and a trailer unit, with a service brake unit, wherein the service brake unit comprises a towing vehicle service brake unit and / or a trailer service brake unit. It further relates to a device for determining the holding capacity of a parking brake unit of a vehicle combination and a computer program for determining the holding capacity of a parking brake unit of a vehicle combination. Vehicle combinations, particularly commercial vehicles, generally have various braking systems: commercial vehicles with trailers typically have a service brake system for the towing vehicle and a separate service brake system for the trailer.A parking brake system is usually designed as a spring-applied brake system and is intended to secure a vehicle combination that has been brought to a standstill and is to be parked against rolling away.

[0003] In some cases, the trailer control system for commercial vehicles is designed so that, when stationary, braking force is provided by the parking brake of the towing vehicle and the service brake of the trailer. However, in the event of a failure of the service brake unit, the parking brake of the towing vehicle must be able to hold the vehicle combination and, if applicable, the trailer safely, even without the braking force of the service brake unit. Therefore, commercial vehicle drivers check whether the vehicle combination remains safely stationary when engaging the parking brake, even if only the parking brake force is applied by spring-applied parking brakes in the towing vehicle and not the service brake force. During extended periods of inactivity, a loss of pressure can occur in the trailer's service brake system. If the vehicle combination cannot be held solely by the parking brake force of the towing vehicle, the required braking force may no longer be provided.For example, on a slope, the vehicle combination could roll away uncontrollably. Therefore, if the driver's inspection reveals that the parking brake unit is unable to hold the vehicle and any trailer independently, the driver must take further safety measures: placing wheel chocks under the tires, applying additional brakes on the trailer, and / or repositioning the vehicle combination.

[0004] This established procedure is prone to error: Human error can lead to the parking brake's holding power being overlooked, or even if the check is performed and reveals insufficient holding power, the vehicle combination is parked without additional securing measures. The commercial vehicle driver may assume that there will be no pressure loss in the trailer's pneumatic service brake system. The driver may not be familiar with the service brake's design in detail and may underestimate the risk of pressure loss. Extended periods of parking a commercial vehicle are particularly common towards the end of a shift or even before the weekend. This is usually preceded by a long, strenuous workday or a long workweek.After prolonged periods of concentration while driving, the ability to focus when parking may be reduced, increasing the risk of inattention when checking the holding power. Such checks must be performed not only when driving without assistance systems, but especially when driving with various levels of automation, up to and including autonomous driving. Therefore, there is a need for new methods to support commercial vehicle drivers in this check or even to perform it entirely. Furthermore, there is a need to develop a device and a computer program to determine the holding power of a parking brake unit on a vehicle combination.

[0005] One object of the invention is to support the parking of vehicle combinations and in particular the determination of the holding capacity of the parking brake, and thus to increase road safety.

[0006] This problem is solved by a method according to claim 1. It is further solved by a device according to claim 16 and a computer program according to claim 17. According to the invention, a method for determining the holding capacity of a parking brake unit of a vehicle combination, the vehicle combination comprising a towing vehicle and a trailer unit, with a service brake unit, wherein the service brake unit comprises a towing vehicle service brake unit and / or a trailer service brake unit, comprises the steps: a) providing an actual holding force by means of the service brake unit and / or the parking brake unit; b) when the vehicle combination is stationary, determining a minimum target holding force, wherein determining the minimum target holding force comprises: b1) reducing the actual holding force, acquiring and storing actual holding force values; b2) upon detection of vehicle movement, increasing the actual holding force;b3) Determining the minimum target holding force from at least one stored actual holding force value and a safety margin; and b-4) Setting the actual holding force to a value that is at least equal to the determined minimum target holding force; c) Comparing the determined minimum target holding force with a threshold holding force of the parking brake unit; and d) Determining the holding capability of the parking brake unit, wherein holding capability exists if the threshold holding force is greater than or equal to the target holding force and wherein no holding capability of the parking brake unit exists if the threshold holding force is less than the target holding force.

[0007] In a first step, an actual holding force is provided to brake the vehicle combination. The service brake unit comprises the various service brake circuits of both the towing vehicle (towing vehicle service brake unit) and any optionally coupled trailer (trailer service brake unit). In addition to or instead of the service brake unit, the actual holding force can also be provided by the parking brake unit. The actual holding force is the sum of the applied braking forces of the parking brake unit and the service brake unit.

[0008] Once the actual holding force is sufficiently high and the vehicle combination has come to a standstill, the minimum target holding force is determined in a second step. The minimum target holding force is the force that the braking system must apply in the given situation to reliably secure the vehicle combination against rolling. The minimum target holding force is situation-dependent: it varies depending on factors such as weather, gradient, load, etc., so it must be determined anew each time the vehicle is parked. During this determination, the actual holding force is reduced, and the corresponding values ​​are recorded and stored until the vehicle combination begins to roll. As soon as such rolling is detected, it is stopped by increasing the actual holding force.Based on at least one actual holding force value and optionally an additional safety margin, the required minimum target holding force is determined, and an actual holding force is set that is at least equal to the minimum target holding force. Advantageously, the at least one actual holding force value is, for example, the last stored value before a roll-in is registered – due to a further reduction in the actual holding force. However, a specific number of stored values ​​around the time of the roll-in can also be used, from which an actual holding force is then calculated, for example, as the mean, median, or maximum of the measured values.

[0009] The safety margin is an additional measure to ensure that the vehicle combination is not only held with a force that is just sufficient to hold the vehicle combination, but with a higher force, so that, for example, even under changing conditions such as an increase in load, snowfall or rain or the onset of wind, the vehicle combination remains secure.

[0010] To determine the required minimum target holding force, the actual holding force value is preferably multiplied by the actual safety margin, or the actual safety margin is added to the actual holding force value. It is also possible to first multiply the minimum target holding force by a first safety margin and then add a second safety margin. Accordingly, the safety margin can be a force value or a dimensionless factor, depending on the calculation. The minimum target holding force can also be determined by combining the safety margin with the actual holding force value in a non-linear manner using mathematical operators, particularly in a progressive or degressive manner.

[0011] In a further process step, the determined minimum target holding force is compared with the threshold holding force of the parking brake unit. If the threshold holding force is greater than or equal to the target holding force, then the parking brake unit is able to hold the vehicle combination. Otherwise, it is unable to do so (the parking brake is not capable of holding). Preferably, the process further comprises, and prior to the step of determining the minimum target holding force from at least one stored actual holding force value and a safety margin, the step of determining a safety margin based on at least one vehicle characteristic and / or based on at least one environmental characteristic. The safety margin can then advantageously be determined and selected depending on the situation. For example, it can be chosen to be larger on steeper slopes, with a heavy load on a busy road, or in residential areas.

[0012] Particularly preferred are vehicle parameters such as vehicle mass, a wear parameter of the parking brake unit, vehicle load, brake disc temperature, tire pressure, actual holding force value, and / or a parameter of a trailer unit of the vehicle combination. These parameters may influence the holding capacity and can then advantageously be used to calculate the safety margin. A vehicle mass can, for example, be the unladen mass without load or the permissible gross vehicle weight, which are advantageously known and stored in a vehicle computer system without needing to be determined separately. It can also be the actual mass of the loaded vehicle combination, which is then, for example, detected by sensors or entered by the driver via a user interface. The mass and / or type of vehicle load can also constitute a vehicle parameter. A wear parameter of the parking brake unit can, for example, be...Existing maintenance information systems can be used as vehicle parameters. Additionally or alternatively, further sensors are provided to determine wear. Heated brake discs or temperatures of other brake components can deform upon cooling and potentially affect braking force, making this parameter another possible vehicle parameter for determining a safety margin. Tire pressure affects the contact area of ​​a tire on the road surface and can advantageously be used as another possible vehicle parameter for calculating holding power. A measured actual holding force, e.g., the force at which rolling was detected, can also be used to calculate a safety margin, so that the safety margin is chosen to be larger, for example, for high actual holding force values.The described vehicle characteristics can be determined analogously for the trailer unit and used as vehicle characteristics. It is possible to use vehicle characteristics of only one towing vehicle, only the trailer unit, or both the towing vehicle and the trailer unit.

[0013] It is also preferred that the environmental parameter be a terrain gradient, an ambient temperature, a location position, and / or a parameter characterizing the ground beneath the vehicle combination. The terrain gradient directly influences what proportion of the weight force acts against the braking force and how much the vehicle combination accelerates when the braking force is released or partially released. The ambient temperature can thermally stress brake components and / or influence the brake's cooling behavior and can therefore advantageously be taken into account when determining the safety margin. A location position, e.g., via GPS, can allow conclusions to be drawn as to whether the truck is in an area where particularly high safety margins might be required. Furthermore, the ground conditions can also advantageously be used to calculate the safety margin. This can, for example,by camera sensors and computer-aided image processing methods, by sensors to determine soil moisture or sensors to determine the reflectance of the soil at certain wavelengths, and used in calculating a safety margin.

[0014] Preferably, following the step of setting the actual holding force to a value that at least corresponds to the determined minimum target holding force, the additional step of checking for a vehicle standstill for a predetermined time interval and, if the vehicle is not stationary within the time interval, repeating the steps of reducing the actual holding force, recording and storing actual holding force values; upon detection of vehicle movement, increasing the actual holding force; determining the minimum target holding force from at least one stored actual holding force value and a safety margin; and setting the actual holding force to a value that at least corresponds to the determined minimum target holding force. This step advantageously provides an additional safety level. It ensures during the predetermined time interval that the determined minimum target holding force is maintained.The set actual holding force, which corresponds at least to the determined target holding force, is actually suitable for securely holding the towing vehicle and any attached trailers. The predetermined time interval is preferably in the range of 0.5 to 10 seconds. Furthermore, it is preferred that the method includes an additional step: applying a predetermined force impulse to at least one drive shaft of the towing vehicle by a drive motor of the towing vehicle at a time during the predetermined time interval. In a sense, the actual holding force is subjected to an additional load test by this force impulse. Advantageously, this method therefore provides a further additional safety level. The magnitude of the force impulse is particularly preferably less than or equal to the calculated safety margin. This method step can then be used to verify whether the safety margin was appropriately determined.This is not the case if the vehicle combination moves in response to the force impulse.

[0015] In a preferred embodiment, the threshold holding force is a predetermined constant. It is preferably stored on the vehicle's system. Advantageously, this allows for a simple comparison of the minimum target holding force with the threshold holding force, which remains constant at all times.

[0016] However, it is also preferred that the threshold holding force be determined based on a vehicle parameter and / or an environmental parameter. Advantageously, it is taken into account that the threshold holding force may depend on a vehicle parameter and / or an environmental parameter.

[0017] It is particularly advantageous to determine the threshold holding force based on the wear condition of the parking brake unit. This is because the holding force of the parking brake can decrease as the parking brake unit wears down. This can be advantageously taken into account when the threshold holding force is determined considering the wear condition.

[0018] It is further preferred to perform the method steps according to claim 1 in a temporal sequence as listed in claim 1. Alternatively, and also preferably, the step of determining the minimum target holding force from at least one stored actual holding force value and a safety margin can be performed simultaneously with or before the step of increasing the actual holding force upon detection of vehicle movement. It is also preferred that the step of determining a minimum target holding force when the vehicle combination is stationary further comprises: checking that the vehicle combination is stationary, wherein checking that the vehicle combination is stationary and the step of reducing the actual holding force, acquiring and storing actual holding force values ​​are performed iteratively until vehicle movement is detected and / or until the actual holding force is zero.By iteratively performing the steps of checking for a standstill of the vehicle combination, reducing the actual holding force, and recording and storing actual holding force values, it is advantageously possible to clearly assign the actual holding force value for which a standstill was last recorded. This value and / or values ​​within this range are suitable stored actual holding force values ​​for determining the minimum target holding force in step b3).

[0019] It is also preferred to perform the additional step b1.2) between steps b1) and b2), namely, detecting the motion state of the vehicle combination and, upon detection of vehicle movement, providing a motion signal, wherein the motion signal is a signal to execute step b2). This advantageously ensures that a corresponding signal to increase the actual holding force is transmitted directly upon detection of vehicle movement. The braking force can then be increased directly, so that any rolling of the vehicle combination is immediately stopped and the vehicle combination is advantageously prevented from accelerating.

[0020] Furthermore, it is preferred that the monitoring of a standstill of the vehicle combination and / or the registration of vehicle movement is carried out based on motion signals output by wheel speed sensors, optical sensors and / or acceleration sensors, in particular by at least one inertial measuring unit. Such sensors are already installed in many vehicles, especially commercial vehicles, so that, advantageously, corresponding motion signals can be used to carry out the method without installing additional sensors for monitoring a standstill or registering vehicle movement.

[0021] Furthermore, it is preferable that the actual holding force is provided exclusively by the towing vehicle. Braking systems of existing trailer units are often only functional when the compressed air supply is sufficiently full. However, when parked, the possibility of a drop in pressure must be taken into account. If the actual holding force is provided exclusively by the towing vehicle, then the actual holding force is advantageously independent of the specific braking system of the trailer unit. In this case, no interfaces between the trailer unit and the towing vehicle are required to transmit the respective braking force of the trailer in such a way that the total applied actual holding force can be easily determined.

[0022] Particularly preferably, the method includes an additional step following the step of determining the holding capability of the parking brake unit: outputting information on the determined holding capability to a communication unit, wherein the communication unit is configured to transmit information to a vehicle driver and / or to an automated vehicle control unit. Preferably, the vehicle driver and / or the automated vehicle control unit can then initiate further steps based on the information, e.g., locking the vehicle combination if holding capability is present, or e.g., reparking the vehicle combination if holding capability is not present.

[0023] According to the invention, a device for determining the holding capacity of a parking brake unit of a vehicle combination comprises a service brake unit and / or a parking brake unit for providing and varying an actual holding force; a service brake force detection unit for detecting and providing actual holding force values; a motion state detection unit for determining the motion state of the vehicle combination and for providing information about the motion state; and a processor unit for determining a minimum target holding force from at least the information about the motion state, a stored actual holding force value, and a safety margin, wherein the processor unit is configured to iteratively process information from the motion state detection unit and to control the service brake unit, wherein the processor unit is configured toto compare the minimum target holding force with a predetermined threshold holding force and to determine the holding capability of the parking brake unit. A computer program according to the invention for determining the holding capability of a parking brake unit of a vehicle combination comprises commands which, when the computer program is executed by a central control unit, execute a method according to one of the preferred embodiments of a method for determining the holding capability of a parking brake unit of a vehicle combination with a service brake unit as described above, according to the first aspect of the invention. It should be understood that the method according to the first aspect of the invention and the computer program according to the third aspect of the invention have the same and similar sub-aspects.as they are set out in particular in the dependent claims. In this respect, for preferred embodiments and further developments of the computer program according to the third aspect of the invention, full reference is made to the preferred further developments and embodiments of the method according to the first aspect of the invention.

[0024] Embodiments of the invention are now described below with reference to the drawings. These drawings are not necessarily intended to represent the embodiments to scale; rather, where this is helpful for clarification, the drawings are presented in a schematic and / or slightly distorted form. With regard to additions to the teachings directly apparent from the drawings, reference is made to the relevant prior art. It should be noted that numerous modifications and changes concerning the form and details of an embodiment can be made without deviating from the general idea of ​​the invention. The features of the invention disclosed in the description, the drawings, and the claims can be essential for the further development of the invention, both individually and in any combination.Furthermore, the invention encompasses all combinations of at least two of the features disclosed in the description, the drawings, and / or the claims. The general idea of ​​the invention is not limited to the exact shape or detail of the preferred embodiments shown and described below, nor is it limited to an object that would be restricted compared to the object claimed in the claims. For specified dimensioning ranges, values ​​lying within the stated limits are also disclosed as limit values ​​and are freely usable and claimable. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar functions. Further advantages, features, and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings; these are shown in:

[0025] Further advantages of the invention are described below using exemplary embodiments. These show:

[0026] Fig. 1 shows a first exemplary sequence of steps for carrying out the procedure;

[0027] Fig. 2 shows a diagram of the actual holding force over time during steps S1 to S2.4;

[0028] Fig. 3 shows a device for determining the holding capacity of a parking brake unit;

[0029] Fig. 4 shows a vehicle combination with a central control unit;

[0030] Fig. 5 shows a second exemplary sequence of steps for carrying out the procedure;

[0031] Fig. 6 shows a further development of the second sequence of steps for carrying out the procedure;

[0032] Fig. 7 shows a third exemplary sequence of steps for carrying out the procedure; and

[0033] Fig. 8 shows a further development of the device according to Fig. 3.

[0034] Figure 1 shows a first sequence of the process steps. A driver or an automated control system of the vehicle combination 1, comprising the towing vehicle 2 and the trailer unit 100 (see Fig. 4), has identified a possible position for parking and stopping the vehicle combination 1 and has driven the vehicle combination 1 to this position. At this position, the process starts with step S1 by providing an actual holding force 25 with the service brake unit 60 and / or the parking brake unit 10. The service brake unit 60 comprises both the towing vehicle service brake unit (60.1) of the towing vehicle 2 and the trailer service brake unit (60.2), see Fig. 4. The vehicle combination 1 is braked in this position and brought to a standstill 85. The actual holding force 25 can be provided at a constant level during braking or gradually increased or decreased until the vehicle combination 1 comes to a standstill.It is also possible to initially use only the service brake unit 60 and provide additional braking force from the parking brake unit 10 at a later time or even when the vehicle is stationary 85. A motion state detection unit 30 monitors the vehicle's stationary state 85 or its movement 55. This unit preferably comprises acceleration sensors 150, wheel speed sensors 130, optical sensors 140, and / or an inertial measuring unit 160. When the vehicle is stationary 85, the second process step begins: determining S2 a minimum target holding force 35. In the embodiment shown here, this step is subdivided into four substeps S2.1–S2.4. In the first substep S2.1, the actual holding force 25 is reduced, and actual holding force values ​​45 are recorded and stored. The reduction S2.1 of the actual holding force 25 can be gradual or in discrete steps.The recording and storage of actual holding force values ​​45 can be continuous. However, if the actual holding force 25 is reduced in stages, the respective actual holding force value 45 can also be recorded and stored once or several times per stage. It is also possible that, during sub-step S2.1, actual holding force values ​​45 are recorded and stored at defined time intervals, e.g., at intervals of 10, 50, 100, 200, or 500 ms. Step S2.1 is carried out until a vehicle movement 55, i.e., the vehicle combination 1 starting to roll, is registered. As soon as this occurs, the actual holding force 25 is increased again (S2.2). A force equilibrium exists during the transition from step S2.1 to step S2.2. Forces acting on this force equilibrium include those in the direction of rolling, in particular a component of the weight force if the vehicle combination 1 is on a slope. This is counteracted by factors such as frictional forces and the actual holding force.Increasing the actual holding force 25 in step S2.2 ensures that it is sufficiently high to quickly stop any vehicle movement 55 of the vehicle combination 1 and prevent the vehicle combination 1 from accelerating in the direction of travel. The increase in the actual holding force 25 can be in one step or gradually. For example, the actual holding force 25 can be increased by a predetermined amount or to the amount that was provided at the end of step S1. In the next step S2.3, the minimum target holding force 35 is determined from the actual holding force values ​​45 recorded and stored in step S2.1 and a safety margin S. This is done using computer-aided means, preferably with a processor unit 40 of the vehicle combination 1. The processor unit 40 can be part of a device 5 for determining the holding capability 75 of a parking brake unit 10.For example, based on the trend of the determined and stored actual holding force values ​​45, a value or range can be identified in which a force equilibrium no longer exists when reducing S2.1 of the actual holding force 25. The minimum target holding force 35 must be greater than such a value or values ​​within such a range.

[0035] In step S2.4, the actual holding force 25 is adjusted from time t3 to a value that is at least equal to the determined minimum target holding force 35. The actual holding force value 25 can also be higher than the determined minimum target holding force 35.

[0036] The actual holding force 35 is preferably provided additively at this point from the braking forces of the service brake unit 60 and the parking brake unit 10. In step S3, the threshold holding force 65 of the parking brake unit 10 is preferably compared with the determined minimum target holding force 35. The purpose of this comparison is, in particular, to determine in the subsequent step S4 whether the parking brake unit 10 can independently generate an actual holding force 25 that is greater than the determined minimum target holding force 35. It is capable of doing so if a threshold holding force 65 of the parking brake unit 10 is greater than or equal to the determined target holding force 35. In this case, the parking brake 10 has a holding capacity 75. Otherwise, it does not have a holding capacity 75. The threshold holding force 65 is a value stored on the vehicle side, for example in a central control unit 50 of the vehicle combination 1 (see

[0037] Fig. 4) is shown. The threshold holding force 65 indicates the maximum force for which the parking brake unit 10 is designed.

[0038] An exemplary curve of the braking force during steps S1 to S2.4 is shown in Fig. 2. A device 5 (see Fig. 3) is used to carry out the procedure. The actual holding force 35 is increased linearly during the first step S1. At time t1, the vehicle combination 1 is stationary. It is also possible that the vehicle combination 1 is stationary before time t1, for example, upon reaching a force Fron. The force Fron is the force at which the vehicle combination 1 actually begins to roll. This force Fron is not known a priori and depends on a multitude of parameters and influencing factors. Such parameters include one or more environmental characteristics 80 (e.g. terrain gradient 80.1, ambient temperature 80.2, location position 80.3 and / or characteristic(s) 80.4 for characterizing a substrate) or one or more vehicle characteristics 90 (e.g. wear parameter 90.2 of the parking brake unit 10, vehicle load 90).3, brake disc temperature 90.4, tire pressure 90.5, an actual holding force value 45 and / or a characteristic value 90.6 of a trailer unit 100 of the vehicle combination 1 ).

[0039] This means that in the first step S1, a higher actual holding force 25 can initially be provided than would actually be necessary for the vehicle to stand still 85. At time t1, the process step S2 starts with substep S2.1. From time t1 to time t2, the actual holding force 25 is reduced in stages. A brake force detection unit 20 detects the actual holding force 25 at each stage. At each stage, the motion state detection unit 30 checks whether the vehicle combination 1 is moving. Both the motion state detection unit 30 and the brake force detection unit 20 are configured to communicate with the processor unit 40.

[0040] The motion state detection unit 30 detects a vehicle movement 55 at time t2, at which the brake force detection unit 20 detects a value less than Fron. This information 145 is processed as a motion signal 125 by the processor unit 40, which then controls the service brake unit 60 and / or the parking brake unit 10 in such a way that the actual holding force 45 is increased (S2.2) and the vehicle combination 1 is brought back to a vehicle standstill 85.

[0041] While the minimum target holding force 35 is determined in step S2.3, the actual holding force 25 remains at a constant plateau in the example shown here. Determining the minimum target holding force 35 in step S2.3 is preferably carried out using a computer program C at the central control unit 50 (see Figure 4) within a very short time, e.g., within less than one millisecond. It should therefore be understood that the time axis in Figure 2 is distorted to better illustrate step S2.3. Furthermore, it should be understood that, unlike what is shown in Figure 2, steps S2.2 and S2.3 can also occur in parallel. While the minimum target holding force 35 is being determined by the processor unit 40 (S2.3), the brake pressure can be increased simultaneously, for example, to increase the braking force of the service brake unit 60.The computer program C can, for example, use the motion signals 125 recorded and stored by the motion state detection unit 30 and the actual holding force values ​​45 recorded and stored by the braking force detection unit 20 to create a log file containing timestamps, actual holding force values ​​45, and information 145 about the motion state. Information 145 about the motion state can be in binary form as "vehicle stationary" 85 or "vehicle moving" 55, or in more detail, e.g., based on current speeds and / or accelerations.

[0042] The log file can be used to determine the actual holding force value 25 for which the end of the vehicle standstill 85 was first recorded. It is also possible that the processor 40 executing the computer program C uses several actual holding force values ​​25 over a certain period to compensate for measurement errors and / or outliers. In the example shown in Figure 2, movement of the vehicle combination 1 was first registered at time t2 because the actual holding force 25 had fallen below the force Fron. To determine the minimum target holding force Fmin-target 35, a safety margin S is added to the actual holding force 25 registered at time t2. The sum of the actual holding force 25 recorded at time t2 and the safety margin S is then the minimum target holding force 35. In step S2.4, the actual holding force 25 is adjusted to a value that corresponds to the determined target holding force 35.Based on this example and by examining the graph in Fig. 2, it becomes clear that the actual holding force 25 measured at time t2 is lower than the force Fron. This is primarily because the detection of movement by the motion state detection unit 30 is discrete in this embodiment. Therefore, to determine the minimum target holding force Fmin-soii 35, another of the determined and stored actual holding force values ​​45 can also be used, preferably, e.g., the last or penultimate value before a movement is registered. Alternatively, several values ​​can be used; for example, a mean, maximum, or median value can be determined from all actual holding force values ​​45 that were recorded and stored within a specific period before a vehicle movement 55 was registered.The choice of a suitable approach depends on the temporal acquisition densities of the motion state determination unit 30 and the braking force acquisition unit 20: If these each acquire measured values ​​at a high temporal density, fewer of the most recently determined and stored actual holding force values ​​45 can be used to determine the minimum target holding force 35. If the acquisition densities are lower, more determined and stored actual holding force values ​​45 may need to be used to determine the minimum target holding force 35.

[0043] In the device 5 shown in Figure 3 for determining the holding capacity 75 of a parking brake unit 10, the processor unit 40 transmits control signals 15 to the service brake unit 60 and the parking brake unit 10. The processor unit 40, in turn, receives information 145 about the state of motion from the state of motion determination unit 30 and actual holding force values ​​45 from the brake force detection unit 20. Dashed arrows indicate that changes in the actual holding force 25, which are provided by the service brake unit 60 and the parking brake unit 10, can affect both the actual holding force values ​​45 detected by the brake force detection unit 20 and the information 145 about the state of motion detected by the state of motion determination unit 30.

[0044] Another embodiment of the claimed method is shown in Fig. 5. In step S1, the actual holding force 25 is provided. The diamond shape indicates that the motion state detection unit 30 detects the two states "vehicle movement" 55 and "vehicle standstill" 85. As long as it detects a vehicle standstill 85, step S2.1, i.e., reducing the actual holding force and detecting and storing actual holding force values ​​45, is carried out until the motion state detection unit 30 detects a vehicle movement 55.

[0045] Then, the path to step S2.2 is selected in the decision tree shown in Fig. 5, i.e., the actual holding force 25 is increased when a vehicle movement 55 is registered. In this embodiment, the movement state is checked by the movement state detection unit 30, and the actual holding force 25 is reduced iteratively by the parking brake unit 10 and / or service brake unit 60. In other embodiments, however, the movement state can also be continuously monitored by the movement state detection unit 30, whereby a movement signal 125 is provided when a vehicle movement 55 is registered in order to increase the actual holding force 25. Steps S2.3 and S2.4 are carried out analogously to the procedure sequence shown in Fig. 1. In the embodiment of the procedure shown in Fig. 5, the additional step S2.5 follows S2.4. After step S2.Once the actual holding force value 45 has been set to at least the value of the determined target holding force 35, step S2.5 uses the motion state determination unit 30 to check whether the vehicle combination 1 is actually stationary for the entire duration of a predefined time interval. If this is not the case, steps S2.2 to S2.4 are repeated analogously to the procedure shown and described in Fig. 1, and a further test for vehicle standstill 85 is then performed in step S2.5. Step S2.5 is thus a safety step in which, after the theoretical determination of the minimum target holding force 35 using the safety margin S in S2.4, an additional practical test is carried out for a predefined time interval 95.

[0046] Another embodiment with a further additional safety level is shown in Fig. 6. Here, during step S2.5, at a predetermined time interval 95, an additional force impulse 105 is exerted by the drive motor 120 of the towing vehicle 1 on a drive shaft 110 of the towing vehicle 1 at time t4. The magnitude of the force impulse 105 is preferably less than the safety margin S, preferably 10%, 30%, or 50% of the safety margin S. This advantageously tests whether, taking the safety margin S into account, the system is actually capable of ensuring a minimum target holding force 35 to guarantee a vehicle standstill 85, even if there is an increase in external, additional forces contrary to the actual holding force 25. Such an increase in external additional forces can occur, for example, if the vehicle mass 90...The force increases, for example due to additional loading or weather conditions such as snow and / or rain. Wind may arise and exert a wind force on the vehicle combination 1. By providing a predetermined force impulse 105, it is advantageously tested whether the holding capacity 75 of the parking brake unit 10 is also given under an additional force impulse 105.

[0047] Another embodiment of carrying out a method according to the invention is illustrated in Fig. 7 by means of a flowchart. The provision S1 of an actual holding force 25 is the start of the method. Subsequently, additional preconditions, S100, which must be met to continue the method, are checked. For example, such a precondition could be a query to the commercial vehicle driver as to whether the method should be carried out. Alternatively, it could be checked whether the parking brake unit 10 and / or service brake unit 60 are already activated and whether the vehicle combination 1 is stationary. This is preferably carried out iteratively until all preconditions are met. The braking force is then optionally redistributed, S110, so that axles of any trailer unit 100 and / or axles without Tristop actuators are not braked.A tristop actuator is designed to provide both a pneumatic service brake force and a mechanical parking brake force via spring forces, thus comprising both a service brake actuator and a spring-applied brake cylinder. In the event of a failure and / or reduction of compressed air in the service brake system, such axles with tristop actuators can provide a parking brake force. If, in the method, the threshold holding force 65 of the parking brakes 10 is compared with the minimum target holding force, it is advantageous to determine the minimum target holding force solely based on braking forces acting on axles with tristop actuators. Therefore, the additional step of redistributing the braking force S110 is preferably provided here.Subsequently, the vehicle's standstill status 85 is checked again (S120) to determine whether the redistribution of braking forces has resulted in any vehicle movement 55. If the vehicle combination 1 is not stationary, the actual holding force 25 on the axles with Tristop actuators is increased again (S170). If it is now determined that the actual holding force 25 of the spring-applied brakes on these axles is insufficient (S140) to achieve a vehicle standstill 85, it can already be concluded that holding the vehicle combination 1 in the selected position is not possible (S150). The procedure can then be terminated at this point (S180), and the communication unit 70 informs the commercial vehicle driver or the (semi-)autonomous central control system 50 of the vehicle combination 1 that holding capability 75 is not present. Preferably, the communication unit 70 requests the commercial vehicle driver or the (semi-)autonomous central control system 50 of the vehicle combination 1.The (semi-)autonomous central control system 50 of the vehicle combination 1 is instructed to select a different parking position, e.g., with a gentler slope 80.1, for parking the vehicle combination 1. If, however, no vehicle movement 55 is detected by the motion state determination unit 30 during the standstill check in S 120, then the vehicle standstill 85 is checked alternately in S 130, and the actual holding force 25 is reduced in S 2.1, until vehicle movement 55 is detected instead of vehicle standstill 85. The procedure is then continued analogously to the process steps S 2.2 to S 2.5 described in Fig. 5. If no vehicle standstill 85 is detected within the predetermined time interval 95 in step S 2.5, steps S 2.2 to S 2.5 are repeated. Before repeating step S2.2, the safety margin S is additionally increased in the embodiment shown in Fig. 7, S160.The safety margin S can, for example, increase by a predetermined amount. Or the current actual holding force value 45 is multiplied by a predetermined factor, e.g., by 1.02, 1.05, or 1.1. The value of the minimum target holding force 35 calculated in step S2.3 is correspondingly higher than in the previous iteration loop. Once the iteration loop, comprising steps S160, S2.2, S2.3, S2.4, and S2.5, has been executed so many times that the standstill check in step S2.5 results in a vehicle standstill 85 after the predetermined time interval 95, the minimum target holding force 35 determined in the last iteration loop is compared in the subsequent step S3 with the threshold holding force 65 of the parking brake unit 10. Based on this comparison, it is then determined in step S4 whether a holding capability 75 of the parking brake unit 10 is given (S4.1 ) or not (S4.2 ).The procedure is then terminated, S180.

[0048] The termination S180 of the process here comprises transmitting information 135 to the commercial vehicle driver and / or the (partially) autonomous central control system 50 of the vehicle combination 1, based on the result of step S4, indicating whether the vehicle combination 1 is capable of stopping or not. For transmitting this information 135, the device 5 may include an additional communication unit 70. Such a further development of the device 5 is shown in Fig. 9. This communication unit 70 may preferably be a display, an indicator light, a haptic signal transmitter, and / or an acoustic signal transmitter, each configured to communicate with the commercial vehicle driver. In addition to the result of the stopping capability test according to step S4, a display or an acoustic signal preferably also transmits a recommendation for action to the commercial vehicle driver.Depending on the result of the holding capability test 75, such a recommendation for action could, for example, be to repark the vehicle combination 1 or to park and lock the vehicle combination 1 at the selected position. For communication with an automated central control unit of a vehicle combination 1, the communication unit 70 is preferably a device for transmitting data to the autonomous driving system. Reference symbol (part of the description).

[0049] 1 vehicle combination

[0050] 2 Towing vehicle

[0051] 5 Device

[0052] 10 Parking brake unit

[0053] 15 Control signal

[0054] 20 Braking force detection unit

[0055] 25 Actual holding force

[0056] 30 Motion State Determination Unit

[0057] 35 minimum target holding force

[0058] 40 processor units

[0059] 45 Actual holding force value

[0060] 50 central control unit

[0061] 55 Vehicle movement

[0062] 60 Service brake unit

[0063] 60.1 Tractor unit service brake

[0064] 60.2 Trailer service brake unit

[0065] 65 Threshold holding force

[0066] 70 communication unit

[0067] 75 holding capacity

[0068] 80 Environmental parameter

[0069] 80.1 Terrain slope

[0070] 80.2 Ambient temperature

[0071] 80.3 Location position

[0072] 80.4 Parameter for characterizing a subsurface

[0073] 85 Vehicle standstill

[0074] 90 Vehicle characteristic

[0075] 90.1 Vehicle mass

[0076] 90.2 Wear parameters

[0077] 90.3 Vehicle loading

[0078] 90.4 Brake disc temperature

[0079] 90.5 tire pressure

[0080] 90.6 Key parameter of the trailer unit

[0081] 95 Time interval 100 Trailer unit

[0082] 105 Force impulse

[0083] 110 drive shaft

[0084] 120 drive motor

[0085] 125 Movement signal

[0086] 130 Wheel speed sensor

[0087] 135 Information on holding capacity

[0088] 140 optical sensor

[0089] 145 Information on the state of movement

[0090] 150 Accelerometer

[0091] 160 inertial measurement units

[0092] C computer program

[0093] K constant

[0094] S safety surcharge

[0095] 51 Providing actual holding power

[0096] 52 Determining a minimum target holding force

[0097] 52.1 Reducing the actual holding force,

[0098] Recording and storing actual holding force values

[0099] 52.2 Increasing the actual holding force

[0100] 52.3 Determining the minimum target holding force from a stored actual holding force value and a safety margin

[0101] 52.4 Adjusting the actual holding force to at least the minimum target holding force

[0102] 52.5 Checking a vehicle standstill for a predetermined time interval

[0103] 53. Comparing the determined minimum target holding force with a threshold holding force of the parking brake unit

[0104] 54 Determining the holding capacity of the parking brake unit

[0105] 54.1 Holding capacity is present

[0106] 54.2 Holding capacity is not present

[0107] S110 Redistributing the actual holding force

[0108] S120 Checking for a vehicle standstill

[0109] S130 Detecting the vehicle's state of motion

[0110] S140 Testing the holding capacity of brakes on axles with Tristop actuators

[0111] S150 Determining inability to park

[0112] S160 Increasing the safety margin

[0113] S170 Increasing braking force on brakes on axles with Tristop actuators S180 Completion

Claims

Patent claims 1. Method for determining the holding capacity of a parking brake unit (10) of a vehicle combination (1), the vehicle combination comprising a towing vehicle (2), a trailer unit (100), and a service brake unit (60), wherein the service brake unit (60) comprises a towing vehicle service brake unit (60.1) and / or a trailer service brake unit (60.2), comprising the steps: a) providing (S1) an actual holding force (25) by means of the service brake unit (60) and / or the parking brake unit (10); b) when the vehicle combination (1) is stationary, determining (S2) a minimum target holding force (35), wherein determining the minimum target holding force (35) comprises: b1) reducing (S2.1) the actual holding force (25), acquiring and storing actual holding force values ​​(45); b2) upon registering a vehicle movement (55), increase (S2.2) the actual holding force (25); b3) determine (S2.3) the minimum target holding force (35) from at least one stored actual holding force value (45) and a safety margin (S); and b4) setting (S2.4) the actual holding force (25) to a value that is at least equal to the determined minimum target holding force (35); c) comparing (S3) the determined minimum target holding force (35) with a threshold holding force (65) of the parking brake unit (10); and d) determining (S4) the holding capability (75) of the parking brake unit (10), wherein holding capability (75) is present if the threshold holding force (65) is greater than or equal to the minimum target holding force (35) and wherein no holding capability (75) of the parking brake unit (10) is present if the threshold holding force (65) is less than the minimum target holding force (35).

2. Method according to claim 1, further comprising prior to step b3): • Determining a safety margin (S) based on at least one vehicle characteristic (90) and / or based on at least one environmental characteristic (80).

3. Method according to claim 2, wherein a vehicle characteristic (90) is a vehicle mass (90.1), a wear parameter (90.2) of the parking brake unit (10), a vehicle load (90.3), a brake disc temperature (90.4), a tire pressure (90.5), an actual holding force value (45) and / or a characteristic (90.6) of a trailer unit (100) of the vehicle combination (1).

4. Method according to claim 2, wherein an environmental parameter (80) is a terrain gradient (80.1), an ambient temperature (80.2), a location position (80.3) and / or a parameter (80.4) for characterizing a subsurface below the vehicle combination (1).

5. Method according to one of the preceding claims, further comprising following step b4): • Check (S2.5) for a vehicle standstill (85) for a predetermined time interval (95) and, if no vehicle standstill (85) occurs within the time interval (95), repeat steps b1 , b2 , b3 and b4.

6. The method of claim 5, further comprising: • Applying a predetermined force impulse (105) to at least one drive shaft (110) of the towing vehicle (2) by a drive motor (120) of the towing vehicle (2) at a time (t4) during the predetermined time interval (95).

7. Method according to any of the preceding claims, wherein the threshold holding force (65) is a predetermined constant (K).

8. Method according to one of the preceding claims, wherein the threshold holding force (65) is determined based on a vehicle characteristic (90) and / or an environmental characteristic (80).

9. Method according to one of the preceding claims, wherein the threshold holding force (65) is determined based on a wear condition (90.2) of the parking brake unit (10).

10. The method of claim 1, wherein the steps are carried out in a temporal sequence according to the enumeration of steps in claim 1.

11. Method according to one of the preceding claims, wherein step b) further comprises: b1.1 ) checking (S120) a standstill of the vehicle combination (1), wherein steps b1 .1 ) and b1 ) are performed iteratively until a vehicle movement (55) is registered and / or until the actual holding force (45) is equal to zero.

12. Method according to one of the preceding claims, wherein step b) between b1) and b2) further comprises: b1.2) detecting (S130) a motion state of the vehicle combination (1) and, upon detection of a vehicle motion (55), providing a motion signal (125), wherein the motion signal (125) is a signal to perform step b2).

13. Method according to one of the preceding claims, wherein the monitoring (S120) of a standstill of the vehicle combination (1 ) and / or the detection (S130) of a vehicle movement (55) is carried out based on wheel speed sensors (130), optical sensors, (140) and / or acceleration sensors (150), in particular on motion signals (125) output by at least one inertial measuring unit (160).

14. Method according to one of the preceding claims, wherein the provision (S1) of the actual holding force (25) is carried out exclusively by the towing vehicle (2).

15. Method according to any of the foregoing claims, further comprising in accordance with S4: Output of information (135) on the determined holding capability (75) to a communication unit (70), wherein the communication unit (70) is designed to transmit information (135) to a vehicle driver and / or to an automated central control unit (50) of the towing vehicle (2).

16. Device (5) for determining a holding capability (75) of a parking brake unit (10) of a vehicle combination (1) , wherein the vehicle combination comprises a towing vehicle (2) and a trailer unit (100), the device (5) comprising: • a service brake unit (60), wherein the service brake unit (60) is a towing vehicle service brake unit (60.1) and / or a trailer service brake unit (60.2), and / or a parking brake unit (10) for providing and varying an actual holding force (25); • a service brake force detection unit (20) for detecting and providing actual holding force values ​​(45); • a motion state determination unit (30) for determining the motion state of the vehicle combination (1) and for providing information (145) about the motion state; and • a processor unit (40) for determining a minimum target holding force from at least the information about the state of motion (145), a stored actual holding force value (45) and a safety margin (S), • wherein the processor unit (40) is configured to iteratively process information (135) from the motion state detection unit (30) and to control the service brake unit (10), • wherein the processor unit (40) is configured to compare the minimum target holding force (35) with a predetermined threshold holding force (65) and to determine a holding capability (75) of the parking brake unit (10).

17. Computer program (C) for determining a holding capability (75) of a parking brake unit (10) of a vehicle combination (1) , comprising commands which, when the computer program (C) is executed by a central control unit (50), perform a method according to one of claims 1-15.

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