Method for monitoring a brake performance of a vehicle, control unit, vehicle, and computer program

Abstract

The invention relates to a method (100) for monitoring a brake performance (B) of a vehicle (50) having a plurality of friction brake units (10), in particular a utility vehicle (50a), wherein the friction brake units (10) are each designed to brake a wheel (11) of the vehicle (50). A brake parameter (12) correlating with a brake performance (B) of the vehicle (50) is determined (110), and an actual value (13i) of a brake variable (13) is determined (120) on the basis of the brake parameter (12), and the actual value (13i) is compared (130) with a target value (13s) of the brake variable (13). If a permissible maximum deviation (13a) of the actual value (13i) from the target value (13s) of the brake variable (13) is exceeded (140), a brake state criterion (14) of one or more of the plurality of friction brake units (10) is detected (150) and checked (160). Depending on the test result (161, 162), a friction brake unit (10) having a reduced specific brake performance (Bs) is identified (170). The invention also relates to a control device (30) for a vehicle (50), to a vehicle (50) and to a computer program (33).

Description

[0001] Method for monitoring braking performance of a vehicle, control unit, vehicle and computer program

[0002] The invention relates to a method for monitoring the braking performance of a vehicle having multiple friction brake units, in particular a commercial vehicle. The invention further relates to a control unit for a vehicle, as well as to a vehicle and a computer program.

[0003] Methods for monitoring the braking performance of vehicles are known from the prior art. For example, EP 3 753 794 A1 discloses a method for monitoring the braking performance of a vehicle. The method comprises: collecting sensor data from various sensors, the sensor data being associated with braking events; determining at least one braking performance value using the sensor data based on at least one of the following analyses: (i) a statistical analysis based on multiple regression; (ii) a brake force loss analysis based on a comparison of wheel speed values ​​of different wheels; (iii) an air suspension pressure analysis based on a comparison of a change in air suspension pressure during braking. The method further comprises detecting a malfunction of at least one brake of at least one wheel based on the determined at least one braking performance value.

[0004] WO 2016 / 030699 A1 discloses a method for monitoring the braking performance of a vehicle. The method comprises, for at least some of the braking events: determining a braking request; determining a vehicle deceleration; defining a first data set of braking events, wherein each braking event in the data set comprises a specific braking request and a specific vehicle deceleration; applying a statistical trend analysis method to the data set to generate a vehicle deceleration and braking request trend; providing a vehicle deceleration and braking request reference; and comparing at least one trend value with at least one reference value. Known methods for monitoring the braking performance of a vehicle predominantly relate to determining or estimating the overall braking performance of the vehicle in order to enable a performance-related assessment of a braking system of the vehicle as a system unit.Component-specific monitoring of braking performance, in which individual braking units of the vehicle can be checked for reduced braking performance, can be very complex in terms of measurement technology or prone to errors due to purely statistical monitoring approaches.

[0005] Against this background, the object of the invention is to provide a method as well as devices and means for monitoring the braking performance of a vehicle, with which a detection and assignment of a reduced specific braking performance to a friction brake unit of the vehicle is made possible in a practical and reliable manner.

[0006] The object is achieved with a method for monitoring the braking performance of a vehicle having multiple friction brake units according to claim 1, as well as with a control unit, a vehicle, and a computer program according to the independent claims. Advantageous embodiments are disclosed in the subclaims, the description, and the figures.

[0007] According to the features of independent claim 1, a method is proposed for monitoring the braking performance of a vehicle having multiple friction brake units, in particular a commercial vehicle, wherein the friction brake units are each configured to brake one wheel of the vehicle. In the method, a braking parameter correlating with the braking performance of the vehicle is determined, and based on the braking parameter, an actual value of a braking variable is determined and the actual value is compared with a target value of the braking variable. If a permissible maximum deviation of the actual value from the target value of the braking variable is exceeded, a braking state criterion of one or more of the multiple friction brake units is recorded and tested, and depending on the test result, a friction brake unit with a reduced specific braking performance is identified.In other words, the method includes monitoring the overall braking performance of the vehicle based on a braking variable and, upon detection of reduced braking performance, additionally testing at least one further, in particular wheel-specific, criterion in order to locate a friction brake unit of the vehicle that is likely causing the reduced braking performance. In other words, the method can have a first and a second method section, wherein the braking performance of the entire vehicle is tested in the first method section, and, upon detection of reduced overall braking performance, at least the wheel-specific braking performance of the vehicle is tested in the second method section, which follows the first method section. Different criteria can be used for this purpose, as described below in connection with various embodiments.

[0008] The proposed method has the advantage of enabling a simple and practical way to locate a friction brake unit with reduced braking performance. This allows for a differentiated assessment of reduced overall braking performance and an appropriate and targeted response to the detection of a specific reduced braking performance in a friction brake unit. For example, the time for servicing a friction brake unit or the time for a roller dynamometer test of the vehicle can be determined precisely and efficiently based on the actual condition of the friction brake unit(s).By using a braking parameter that correlates with the vehicle's braking performance on the one hand, and by additionally evaluating wheel-specific data to identify a friction brake unit with reduced specific braking performance on the other, the method demonstrates high detection accuracy and reliability with reduced susceptibility to errors. The braking condition criterion used to identify a friction brake unit with reduced specific braking performance can, as explained in more detail below using exemplary braking condition criteria, be detected simply and efficiently using vehicle sensors already provided on the vehicle and / or with easy-to-install and cost-effective sensors.

[0009] Furthermore, since a wheel-specific analysis of the friction brake units is only carried out in the event of a detected reduction in overall performance, the control effort required to carry out the procedure is reduced compared to conventional procedures for individual braking performance monitoring.

[0010] The method for monitoring braking performance relates to a vehicle having a plurality of friction brake units, each of which is configured to brake a wheel of the vehicle. A plurality of friction brake units is understood to mean, in particular, at least two friction brake units. A friction brake unit can, for example, be a pneumatically, in particular electropneumatically, activated friction brake. A friction brake unit can have one or more friction brake elements with a brake pad. Each friction brake unit of the vehicle can be assigned to a wheel of the vehicle. To monitor braking performance, a braking parameter correlating with a braking performance of the vehicle can be determined, particularly during a deceleration process in which the friction brake units are activated, and an actual value of a braking variable can be determined based on the braking parameter, wherein the actual value is compared with a target value of the braking variable.A braking parameter correlating with the vehicle's braking performance can be a measurable dynamic variable that is directly or indirectly related to the braking performance. Such a braking parameter can, for example, be a vehicle deceleration or a change in the bellows pressure of a spring bellows of a compressed air-based suspension system of the vehicle. The determination of a braking parameter correlating with the vehicle's braking performance can also include the recording of a plurality of different braking parameters correlating with the vehicle's braking performance. The braking variable, whose actual value is determined within the framework of the method based on the braking parameter or parameters, can be, for example, a braking force or a deceleration of the vehicle. The target value of the braking variable can, for example, be a value of the braking variable specified by the control system.To monitor braking performance, a repeated, in particular continuous, sequence of determining the braking parameter, determining the actual value of the braking variable, and comparing the actual value with the target value of the braking variable can be provided. The method for monitoring braking performance can be carried out in particular during driving operation of the vehicle, and in particular during a deceleration process of the vehicle. The vehicle can in particular be a commercial vehicle, in particular a trailer vehicle such as a semi-trailer. In principle, however, the method is also applicable to passenger cars or towing vehicles, for example semi-trailer tractors. The friction brake units of the vehicle can, for example, be controlled via an electro-pneumatic braking system of the vehicle.The vehicle may have a control unit for controlling the electropneumatic braking system, so that the friction brake units can be activated jointly or individually by the control unit using electropneumatic signals transmitted from the control unit to the friction brake units via the braking system. The control unit may, for example, be designed as the vehicle's brake control unit.

[0011] According to one embodiment, checking a braking condition criterion of one or more of the multiple friction brake units can include checking a braking condition criterion of all friction brake units. Checking a braking condition criterion can, for example, include comparing a determined instantaneous value representing a current braking condition of the friction brake unit with a predetermined limit value. A braking condition criterion can be a variable or test condition representative of a condition of the friction brake unit. The braking condition criterion can, in particular, be a wheel-specific variable or test condition.For example, the braking condition criterion can be a sensory variable and / or an event criterion that can be evaluated by the control system. For the evaluation of this criterion, stored event data from a maintenance history or a driving stability system, such as stored event data from an ABS (anti-lock braking system), can be used. A specific braking power of a friction brake unit can be a braking power related to an individual friction brake unit. A specific braking power can therefore be distinguished from the overall braking power of the vehicle. The specific braking power can also be referred to as wheel-specific braking power.

[0012] If an evaluation of the braking condition criterion of the friction brake units does not reveal an identifiable friction brake unit with reduced specific braking performance, according to various embodiments, for example, the monitoring of the braking performance can be continued, the braking condition criterion can be checked again, a different braking condition criterion can be used for a supplementary test, or a decision can be made regarding reduced braking performance of the entire vehicle. Reduced braking performance of the entire vehicle can occur, for example, due to a so-called sleepiness of the friction brake units, in which usually several friction brake units of the vehicle are affected by a reduced specific braking performance, for example due to a reduced activation frequency.

[0013] According to one embodiment, the braking condition criterion can be recorded for several or all of the multiple friction brake units of the vehicle, and the braking condition criterion recorded for each of the several or all of the multiple friction brake units can be compared for testing purposes. This makes it easy to assess the braking condition criterion of the friction brake units independently of predefined comparison criteria, thus providing a flexible testing concept. For example, if a friction brake unit significantly deviates from other friction brake units with regard to the tested braking condition criterion, it can be concluded that this friction brake unit has a reduced specific braking performance.

[0014] According to one embodiment, a plurality of different braking condition criteria of one or more of the plurality of friction brake units can be recorded and evaluated in conjunction with one another for testing. This makes it possible to achieve increased reliability and reduced susceptibility to errors when identifying a friction brake unit with reduced specific braking performance. The plurality of different braking condition criteria can be evaluated, in particular, for all friction brake units of the vehicle. At least two different braking condition criteria can be evaluated jointly, for example, with a defined and / or link, a predetermined weighting, or in the form of a verification of a test result of a test of a first braking condition criterion using a test result of a test of a second braking condition criterion.Such verification can, for example, be performed in principle or only if the test of the first braking condition criterion produces an ambiguous or incomplete test result. According to one embodiment, the braking condition criterion can be a temperature value of the friction brake unit. By establishing a direct relationship between a specific braking power and a temperature of the friction brake unit, a reliable identification of a friction brake unit with reduced specific braking power can be achieved. In addition, a temperature of the friction brake unit can be recorded with high accuracy at the friction brake unit. The temperature value can, for example, be a value of a brake disc temperature, a brake caliper temperature, or a brake pad temperature. These can also be recorded and evaluated in combination with one another.To test the braking condition criterion, the temperature value of the friction brake unit can be compared, for example, with a specified limit value and / or with the temperature values ​​of other friction brake units. For example, if a specified minimum temperature value is undershot and / or the temperature value of the friction brake unit is significantly lower than the temperature values ​​of other friction brake units, it can be concluded that the friction brake unit has a reduced specific braking performance.

[0015] According to one embodiment, the braking condition criterion can be a temperature value of the vehicle wheel that the friction brake unit is configured to brake. A direct correlation between a specific braking performance and a wheel temperature can thereby reliably identify a friction brake unit with a reduced specific braking performance. The wheel temperature value can, for example, refer to a tire temperature, a rim temperature, a wheel hub temperature, and / or a wheel bearing temperature of the wheel. The tire temperature or rim temperature of the wheel can, for example, be detected using a tire sensor that is already provided on the vehicle and is additionally assigned to a tire pressure monitoring system and can be configured to monitor a tire pressure and a tire temperature.This allows a temperature value to be recorded efficiently as a braking condition criterion without having to install a separate temperature sensor on the vehicle wheel. Alternatively or additionally, a specially provided temperature sensor for recording a temperature value of the wheel as a braking condition criterion can be arranged on the vehicle wheel. To check the braking condition criterion, the temperature value of the wheel can be compared, for example, with a predetermined limit value and / or with temperature values ​​of other wheels of the vehicle. For example, if a predetermined minimum temperature value is undershot and / or if the temperature value of the wheel is significantly lower than the temperature values ​​of other wheels, it can be concluded that a friction brake unit has a reduced specific braking performance.

[0016] According to one embodiment, the braking condition criterion can be a brake pad condition of the friction brake unit. A direct correlation between the brake pad condition of the friction brake unit and its specific braking performance can thereby achieve reliable identification of a friction brake unit with reduced specific braking performance. The brake pad condition of the friction brake unit is an easily ascertainable and meaningful braking condition criterion. The brake pad condition can be measured, for example, using a brake pad sensor to detect the residual thickness of the brake pad. Alternatively or additionally, the brake pad condition can be determined using data stored in the control system, for example, based on the time of the last brake pad replacement and / or estimated using a braking operation counter.To test the braking condition criterion, the brake pad condition of the friction brake unit can be compared, for example, with a specified limit value and / or with the brake pad conditions of other friction brake units in the vehicle. For example, if the brake pad thickness falls below a specified minimum and / or if the brake pad condition of the friction brake unit differs significantly from the brake pad conditions of other friction brake units, it can be concluded that the friction brake unit has a reduced specific braking performance.

[0017] According to one embodiment, the braking condition criterion can be wheel slip of the wheel of the vehicle for which the friction brake unit is configured to brake. A direct correlation between specific braking power and wheel slip of the wheel can thereby achieve reliable identification of a friction brake unit with reduced specific braking power. The wheel slip can be determined, in particular, based on a wheel speed that can be detected by a speed sensor arranged on the wheel, wherein, in particular, the speeds of several wheels of the vehicle can be evaluated together to determine the wheel slip. Modern vehicles typically have speed sensors on the wheels to monitor the wheel speeds, so that using wheel slip as a braking condition criterion can advantageously be used without the need for an additional sensor for the braking performance monitoring method.To test the braking condition criterion, the wheel slip of the wheel can be compared, for example, with a specified limit value and / or with wheel slip data from other wheels. A comparison with additional wheel slip data can be advantageous in view of complex, for example, driving dynamic, causes of a changed wheel slip. For example, if the wheel slip of the wheel differs significantly from that of other wheels, it can be concluded that a friction brake unit has a reduced specific braking performance.

[0018] According to one embodiment, the braking condition criterion can be a bellows pressure of a spring bellows arranged on the wheel of a vehicle's suspension system. A direct correlation between a specific braking performance and a bellows pressure of a spring bellows on the braked wheel can thereby reliably identify a friction brake unit with a reduced specific braking performance. For example, vehicles with an air-sprung independent wheel suspension can each have a dedicated spring bellows supplied with compressed air and a pressure sensor on several or all wheels of the vehicle, allowing a wheel-specific evaluation of the specific braking performance based on the pressure values ​​of the respective bellows pressure sensors.For example, if the bellows pressure of a wheel's spring bellows differs significantly from that of spring bellows on other wheels, or if the bellows pressure of a wheel's spring bellows deviates from a predetermined limit, it can be concluded that a friction brake unit has reduced specific braking performance. Furthermore, a bellows pressure averaged across all detected bellows pressure sensors of the wheels can be used to assess the braking performance of the vehicle as a whole, so that the bellows pressure sensors provide different evaluation options that can be used for the proposed method. According to one embodiment, the braking state criterion can be related to the dynamic driving behavior of the wheel of the vehicle for which the friction brake unit is configured to brake. For example, an evaluation of detected dynamic driving events, such as an event history of an ABS system, can be carried out to check the braking state criterion.For example, if a wheel of the vehicle is frequently affected by a dynamic driving event or a stability control measure, such as an ABS response, this can indicate a reduced specific braking performance of the friction brake unit assigned to that wheel. In modern vehicles, dynamic driving data can be recorded, and in particular stored, as part of driving stability programs, so that such dynamic driving data and events can be easily incorporated into the control system when monitoring braking performance.

[0019] According to one embodiment, the braking parameter correlating with the braking performance of the vehicle can be a bellows pressure of a suspension system of the vehicle. The braking parameter can, in particular, be a change in the bellows pressure of a spring bellow of an air-pressure-based suspension system of the vehicle. A braking action on the vehicle can lead to a force acting on the spring bellow of the suspension system. A bellows pressure or a change in the bellows pressure can therefore be representative of a braking variable such as a braking force or deceleration of the vehicle. Based on the bellows pressure or the change in the bellows pressure, the overall braking performance of the vehicle can thus be reliably and easily recorded and monitored.The described embodiment enables a comparatively simple, so-called “onboard” determination of braking variables, without the need to place force sensors or strain gauges, for example, to determine a braking variable of the vehicle, the use of which can be associated with high effort and high costs.

[0020] The object underlying the invention is further achieved with a control unit for a vehicle, in particular for a commercial vehicle, which is configured to carry out the method according to one of the features described above. The proposed control unit can also achieve the above-described advantages of a practical and reliable determination and assignment of a reduced specific braking power to a friction brake unit of the vehicle. The control unit can be configured to control an electropneumatic braking system of the vehicle. The control unit can be configured to activate the friction brake units of the vehicle via the electropneumatic braking system. The control unit can be designed, for example, as a brake control unit of the vehicle.The control unit can be signal-connected to one or more sensors or to one or more other control devices of the vehicle, for example, to a temperature sensor, a brake pad sensor, a tire sensor, a speed sensor, a bellows pressure sensor, a suspension system controller, a tire pressure monitoring system controller, and / or a driving stability system controller. The control unit can, for example, be a processor-based control unit. The control unit can, for example, have a computing unit for processing data, in particular for executing machine-readable instructions of a computer program, and a memory unit for storing data, in particular for storing a computer program with machine-readable instructions.Furthermore, comparison and reference values, such as a target value or a limit value according to one of the previously described embodiments, can be stored in the memory unit.

[0021] The object underlying the invention is further achieved with a vehicle, in particular a commercial vehicle, wherein the vehicle has a plurality of friction brake units, each configured to brake a wheel of the vehicle, and a control unit according to one of the above-described features. The above-described advantages of a practical and reliable determination and assignment of a reduced specific braking power to a friction brake unit of the vehicle can also be achieved with the proposed vehicle.

[0022] According to one embodiment, the vehicle can have a temperature sensor, brake pad sensor, tire sensor, and / or speed sensor arranged on a friction brake unit and / or on a wheel of the vehicle. This makes it easy to identify a friction brake unit with reduced specific braking performance as part of monitoring the braking performance of the vehicle using at least one of the aforementioned vehicle sensors. Depending on the embodiment, the vehicle sensor can be signal-connected to another control device of the vehicle in order to supply it with sensor data, thus implementing efficient multiple use of the vehicle sensor. Examples of other control devices that can utilize at least one of the aforementioned vehicle sensors are a tire pressure monitoring system controller and a driving stability system controller of the vehicle.The aforementioned vehicle sensors can be connected or connectable to the control unit. Alternatively or additionally, the control unit can be connected or connectable to at least one further control device, for example, the suspension system control and / or the driving stability system control, via which the acquired sensor data can be communicated to the control unit.

[0023] According to one embodiment, the vehicle can have a suspension system with a spring bellows and a bellows pressure sensor. Based on a bellows pressure or a bellows pressure change that can be detected with the bellows pressure sensor, the braking performance of the vehicle can be reliably and easily detected and monitored and / or a friction brake unit with reduced specific braking performance can be identified. The detected bellows pressure can also be used as a control and regulating variable of the suspension system, so that the bellows pressure sensor has an advantageous multiple function. The bellows pressure sensor can, for example, be connected or connectable to the control unit via signaling. Alternatively or additionally, the control unit can be connected or connectable to a suspension system controller, via which a detected bellows pressure or a bellows pressure change can be communicated to the control unit.

[0024] According to one embodiment, the vehicle can be designed as a trailer. For example, the trailer can be configured as a semi-trailer. The trailer can be connected to a towing vehicle, for example a tractor unit, to form a vehicle combination. With a vehicle according to the proposed features, which is designed as a trailer, it is advantageously possible to monitor the braking performance of the trailer independently of influences from a towing vehicle connected to the trailer. Particularly in commercial vehicle applications in which trailers can have a large number of wheels and friction brake units due to their transport task and their associated dimensions, individual identification of friction brake units with reduced specific braking performance can be associated with economic advantages, for example with regard to more efficient maintenance.

[0025] The object underlying the invention is further achieved with a computer program having machine-readable instructions which, when executed by a computing unit, cause the computing unit to perform the method according to one of the above-described features. The proposed computer program can also achieve the above-described advantages of a practical and reliable determination and assignment of a reduced specific braking power to a friction brake unit of the vehicle. The computing unit can, for example, be a computing unit of the above-described control unit of the vehicle. The computer program can, for example, be stored in a memory unit of the control unit. The invention can further comprise a machine-readable storage medium on which the above-described computer program is stored.

[0026] In general, unless explicitly defined otherwise, the words “ein / eine” are not to be understood as numbers, but as indefinite articles with the literal meaning of “at least one”.

[0027] The invention permits various embodiments and is explained in more detail below using an exemplary embodiment with the accompanying drawings. They show schematically:

[0028] Fig. 1 is a schematic diagram of a vehicle combination with a vehicle having several friction brake units in a side view;

[0029] Fig. 2 is a simplified flow diagram of a method for monitoring a braking performance of the vehicle; and

[0030] Fig. 3 shows a schematic diagram of a control unit of the vehicle for implementing the method. Fig. 1 shows a schematic diagram of a vehicle combination 53 with a towing vehicle 52 and a vehicle 50 configured as a trailer 51. According to the exemplary embodiment shown, the vehicle combination 53 is configured as a semitrailer, with the towing vehicle 52 being a tractor unit and the trailer 51 being a semitrailer. The towing vehicle 52 and the trailer 51 can be considered commercial vehicles 50a.

[0031] As can be seen from Fig. 1, the vehicle 50 has a plurality of friction brake units 10, which are shown by way of example on two wheels 11 of different vehicle axles 58 of the vehicle 50. The friction brake units 10 are each designed to brake the wheel 11 on which they are arranged. The friction brake units 10 can in particular be electropneumatically activated friction brakes. The friction brake units 10 can each have one or more friction brake elements (not shown in detail) with a brake pad. According to the selected exemplary embodiment, a temperature sensor 20 and a brake pad sensor 22 are each arranged on the friction brake units 10. According to the selected exemplary embodiment, a tire sensor 21 and a speed sensor 23 are each arranged on the wheels 11. The vehicle 50 has a control unit 30 for carrying out the method 100 described below for monitoring a braking power B of the vehicle 50.The control unit 30 can, for example, be designed as a brake control unit of the vehicle 50. The control unit 30 is connected to the friction brake units 10 via signal connections 57 and an electropneumatic brake system (not shown in detail) for activating the friction brake units 10. The control unit 30 is also signal-connected or connectable to the aforementioned temperature sensors 20, brake pad sensors 22, tire sensors 21, and speed sensors 23, whereby related signal connections are not shown in detail in Fig. 1 for reasons of clarity. The control unit 30 is further connected via a trailer interface 54 and signal connections 57 to a towing vehicle control system 55 of the towing vehicle 52, in particular to receive a deceleration signal and activate the friction brake units 10.The towing vehicle control 55 of the towing vehicle 52 can further be configured to activate a friction brake unit 10 of a wheel 11 of the towing vehicle 52. The control unit 30 is further connected via signal connections 57 to a driving stability system control 24 and a suspension system control 27 to a bellows pressure sensor 26 of a suspension system 25 of the vehicle 50, said sensor being arranged in or on a spring bellows 26b.

[0032] According to the exemplary embodiment shown, the control unit 30 and the vehicle 50 designed as a trailer vehicle 51 are designed to carry out the method 100 for monitoring a braking power B of the vehicle 50, which is described below with reference to FIG. 2 in conjunction with FIG. 3.

[0033] For this purpose, Fig. 2 shows a simplified flow diagram of the method 100 for monitoring the braking power B. Fig. 3 shows a schematic diagram of the control unit 30 of the vehicle 50. The control unit 30 according to the exemplary embodiment shown has, for example, a processor-based computing unit 31, a memory unit 32, a plurality of signal inputs 35 and a plurality of signal outputs 36. A computer program 33 can be stored in the memory unit 32, which includes machine-readable instructions 34 which, when the instructions 34 are executed by the computing unit 31, cause the computing unit 31 to carry out the method 100 explained below.

[0034] The method 100 begins, as illustrated in Fig. 2, with the method start 101 of the method 100. The method start 101 occurs in particular during driving operation of the vehicle 50 and can be triggered, for example, by receipt of a deceleration request at the control unit 30 for activating the friction brake units 10. The friction brake units 10 are then activated and, in a step 110, a braking parameter 12, which correlates with a braking power B of the vehicle 50 and is shown schematically in Fig. 3, is determined by means of the control unit 30, in particular continuously. Based on the braking parameter 12, an actual value 13i of a braking variable 13 is determined by means of the control unit 30 in a step 120, as shown schematically in Fig. 3, and in a further step 130 is compared with a target value 13s of the braking variable 13, which is stored, for example, in the memory unit 32 of the controller 30.The braking parameter 12 can be a measurable dynamic variable that is directly or indirectly related to a braking performance B of the vehicle 50, for example, a vehicle deceleration of the vehicle 50 or, as explained below, a change in a bellows pressure 26a of a spring bellows 26b of the air suspension system 25 of the vehicle 50. The braking variable 13 derived therefrom can be, for example, a braking force or deceleration of the vehicle 50.

[0035] If the comparison results in a comparison result 141 that a permissible maximum deviation 13a between the actual value 13i and the target value 13s is not exceeded, the method 100 can return to step 110 and continue with the determination of the braking parameter 12. If the comparison results in a comparison result 140 that a permissible maximum deviation 13a between the actual value 13i and the target value 13s is exceeded, at least one braking state criterion 14 of one or more of the plurality of friction brake units 10 is detected in a subsequent step 150 and checked in a further step 160, for example, for an undershoot or overshoot of a predetermined limit value and / or for a deviation of a friction brake unit 10 from other friction brake units 10 with regard to the braking state criterion 14 or the braking state criteria 14.In particular, the braking condition criterion 14 can be recorded for all friction brake units 10 of the vehicle 50 and compared with each other for testing. If, for example, the test results in test result 161, a significant deviation of one friction brake unit 10 from other friction brake units 10 with regard to the braking condition criterion 14 or the braking condition criteria 14, the deviating friction brake unit 10 is identified in a step 170 as a friction brake unit 10 with a reduced specific braking power Bs. If the test results in test result 162, no significant deviation of a friction brake unit 10, an overall reduced braking power B of the vehicle 50 can be determined in a step 171. Alternatively, it is conceivable, for example, to continue monitoring the braking power B, to test the braking condition criterion 14 or the braking condition criteria 14 again, or to evaluate other braking condition criteria 14.The described test results 161 , 162 regarding a reduced braking performance B and / or a reduced specific braking performance B. s can, for example, be output in a manner perceptible to a driver of the towing vehicle 52 via a display device 37 shown in Fig. 3, which is connected or connectable to a signal output 36 of the control unit 30 and / or can be forwarded externally to the vehicle via a communication interface 38, for example to a fleet operator of the vehicle 50. The method 100 is concluded with the end of the method 180.

[0036] Fig. 3 schematically shows examples of sensor variables and event data that can be evaluated by the control unit 30 as braking state criterion 14. The described braking state criterion 14 can, for example, be a temperature value 20a of the friction brake unit 10. The temperature value 20a can be provided by a temperature sensor 20, shown schematically in Figs. 1 and 3, arranged on the friction brake unit 10 and, as shown in Fig. 3, fed to the control unit 30 via a signal input 35. The temperature value 20a can, for example, be compared with a limit value and / or with temperature values ​​20a of other friction brake units 10 of the vehicle 50. The described braking state criterion 14 can, for example, be a temperature value 21a of the wheel 11, which the friction brake unit 10 is configured to brake.The temperature value 21a can, for example, refer to a tire temperature, a rim temperature, a wheel hub temperature, or a wheel bearing temperature of the wheel 11. The temperature value 21a can, for example, be provided by a tire sensor 21 arranged on the wheel 11, shown schematically in Figs. 1 and 3, and can be fed to the control unit 30 via a signal input 35, as shown in Fig. 3. The temperature value 21a can, for example, be compared with a limit value and / or with temperature values ​​21a of other wheels 11 of the vehicle 50. The described braking state criterion 14 can, for example, be a brake pad state 22a of the friction brake unit 10. The brake pad state 22a can be provided by a brake pad sensor 22 arranged on the friction brake unit 10, shown schematically in Figs. 1 and 3, and can be fed to the control unit 30 via a signal input 35, as shown in Fig. 3.The brake pad condition 22a can, for example, be compared with a limit value and / or with brake pad conditions 22a of other friction brake units 10 of the vehicle 50. The described braking condition criterion 14 can, for example, be a wheel slip 23b of the wheel 11 of the vehicle 50, which the friction brake unit 10 is configured to brake. The wheel slip 23b can be determined by the control unit 30 based on a rotational speed 23a, which can be detected by a rotational speed sensor 23 arranged on the wheel 11, shown schematically in Figs. 1 and 3. The wheel slip 23b can, for example, be compared with a limit value and / or with wheel slip values ​​of other wheels 11. By means of the various sensor variables that can be transmitted to the control unit 30 and used as braking state criteria 14, several different braking state criteria 14 of the friction brake units 10 can advantageously be detected and evaluated for testing, in particular in conjunction with one another.Alternatively or in addition to the described direct connection between the aforementioned vehicle sensors and the control unit 30, the control unit 30 can be connected or connectable via signal technology to other control devices of the vehicle 50 in order to receive sensor variables usable as braking state criteria 14 or, for example, event data via the other control devices. Thus, as shown in Figs. 1 and 3, the control unit 30 can be connected or connectable via a signal connection 57 to a driving stability system controller 24 of the vehicle 30 in order to be able to evaluate a braking state criterion 14 related to a driving dynamic behavior 24a of the wheel 11 of the vehicle 50.For example, stored event data from a driving stability system embodied as an ABS device can be used for this purpose, for example in order to be able to use the more frequent impact of a wheel 11 by a driving stabilization measure compared to other wheels 11 as a braking state criterion 14. Furthermore, the control unit 30, as shown in Figs. 1 and 3, can be connected or connectable via a signal connection 57 to a tire pressure monitoring system controller 56 of the vehicle 30 in order, for example, to receive and evaluate a temperature value 21a of the wheel 11 detected by a tire sensor 21 of a tire pressure monitoring system. Furthermore, the control unit 30, as shown in Figs. 1 and 3, can be connected or connectable via a signal connection 57 to a towing vehicle controller 55 of the towing vehicle 52 in order to receive a deceleration signal representing a deceleration request for activating the friction brake units 10.Furthermore, as shown in Figs. 1 and 3, the control unit 30 can be connected or connectable via a signal connection 57 to a suspension system controller 27 and / or to a bellows pressure sensor 26 of a suspension system 25 in order to be able to use a bellows pressure 26a as a braking parameter 12 correlating with the braking performance B of the vehicle 50 for determining the braking variable 13. Alternatively or additionally, a bellows pressure detected by the bellows pressure sensor 26 or a detected bellows pressure change can be used as a braking state criterion 14 for identifying a friction brake unit 10 with a reduced specific braking performance B. s be used.

[0037] With the method 100 described above, the control unit 30, the vehicle 50 and the computer program 33, the braking power B of the vehicle 50 can advantageously be monitored, with which a determination and allocation of a reduced specific braking power Bs to a friction brake unit 10 of the vehicle 50 can be achieved in a practical and reliable manner. The localization of a friction brake unit 10 with reduced specific braking power Bs made possible in this way allows a differentiated assessment of an overall reduced braking power B of the vehicle 50 and a targeted reaction to the detection of the reduced specific braking power B sFor example, a maintenance time for the affected friction brake unit 10 can be determined precisely and efficiently depending on the detected reduced specific braking power Bs. Furthermore, since a wheel-specific analysis of the friction brake units 10 only takes place when a reduced braking power B of the vehicle 50 is detected, the control effort required to implement the method 100 is reduced compared to conventional methods for individual braking performance monitoring. Due to data from vehicle sensors of other vehicle systems that can be used as braking state criterion 14, the invention can advantageously be implemented without additional sensor installations according to some embodiments.

[0038] Reference symbol (part of the description)

[0039] 10 Friction brake unit

[0040] 11 wheels

[0041] 12 braking parameters

[0042] 13 Brake size

[0043] 13a Maximum permissible deviation actual value / setpoint

[0044] 13i Actual value of brake variable

[0045] 13s setpoint brake size

[0046] 14 Brake condition criterion

[0047] 20 Temperature sensor

[0048] 20a Temperature value friction brake unit

[0049] 21 Tire sensor

[0050] 21a Temperature value wheel

[0051] 22 Brake pad sensor

[0052] 22a Brake pad condition

[0053] 23 Speed ​​sensor

[0054] 23a speed

[0055] 23b Wheel slip

[0056] 24 Driving stability system control

[0057] 24a driving dynamics

[0058] 25 Suspension system

[0059] 26 Bellows pressure sensor

[0060] 26a Bellows pressure

[0061] 26b Bellows

[0062] 27 Suspension system control

[0063] 30 Control unit

[0064] 31 computing unit

[0065] 32 storage units

[0066] 33 computer program

[0067] 34 instructions

[0068] 35 Signal input

[0069] 36 Signal output

[0070] 37 Display device 8 Communication interface 0 Vehicle 0a Commercial vehicle 1 Trailer 2 Towing vehicle 3 Vehicle combination 4 Trailer interface 5 Towing vehicle control 6 Tire pressure monitoring system control 7 Signal connection 8 Vehicle axle

[0071] 100 procedures

[0072] 101 Start of procedure

[0073] 110 Determination of braking parameters

[0074] 120 Determination of actual value of brake size

[0075] 130 Comparison of actual value / setpoint brake size

[0076] 140 Exceeding the permissible maximum deviation

[0077] 141 no exceeding of permissible maximum deviation

[0078] 150 Detection of brake condition criterion

[0079] 160 Test brake condition criterion

[0080] 161 significant deviation

[0081] 162 no significant deviation

[0082] 170 Identification of friction brake unit with reduced specific braking performance

[0083] 171 Determination of overall reduced braking performance

[0084] 180 End of procedure B Braking power Bs specific braking power

Claims

Patent claims 1. A method (100) for monitoring a braking performance (B) of a vehicle (50), in particular a commercial vehicle (50a), having a plurality of friction brake units (10), wherein the friction brake units (10) are each configured to brake a wheel (11) of the vehicle (50), wherein a braking parameter (12) correlating with a braking performance (B) of the vehicle (50) is determined (110), and an actual value (13i) of a braking variable (13) is determined (120) based on the braking parameter (12), wherein the actual value (13i) is compared (130) with a target value (13s) of the braking variable (13), characterized in that if a permissible maximum deviation (13a) of the actual value (13i) from the target value (13s) of the braking variable (13) is exceeded (140), a braking state criterion (14) of one or more of the plurality of friction brake units (10) is recorded (150) and tested (160) and that depending on the test result (161, 162) a friction brake unit (10) with a reduced specific braking power (Bs ) is identified (170).

2. Method (100) according to claim 1, characterized in that the braking state criterion (14) is recorded (150) for several or all of the plurality of friction brake units (10) of the vehicle (50) and is compared with one another for testing (160) for the friction brake units (14).

3. Method (100) according to claim 1 or 2, characterized in that several different braking state criteria (14) of one or more of the plurality of friction brake units (10) are recorded (150) and evaluated in conjunction with one another for testing (160).

4. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is a temperature value (20a) of the friction brake unit (10).

5. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is a temperature value (21a) of the wheel (11) of the vehicle (50) for the braking of which the friction brake unit (10) is configured.

6. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is a brake pad state (22a) of the friction brake unit (10).

7. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is a wheel slip (23b) of the wheel (11) of the vehicle (50) for the braking of which the friction brake unit (10) is configured.

8. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is a bellows pressure (26a) of a spring bellows (26b) of a suspension system (25) of the vehicle (50) arranged on the wheel (11).

9. Method (100) according to one of the preceding claims, characterized in that the braking state criterion (14) is related to a driving dynamic behavior (24a) of the wheel (11) of the vehicle (50) for the braking of which the friction brake unit (10) is configured.

10. Method (100) according to one of the preceding claims, characterized in that the braking parameter (12) correlating with the braking performance (B) of the vehicle (50) is a bellows pressure (26a) of a suspension system (25) of the vehicle (50).

11. Control unit (30) for a vehicle (50), in particular a commercial vehicle (50a), which is designed to carry out the method (100) according to one of claims 1 to 10.

12. Vehicle (50), in particular a commercial vehicle (50a), with a plurality of friction brake units (10), each of which is configured to brake a wheel (11) of the vehicle (50), and a control unit (30) according to claim 11.

13. Vehicle (50) according to claim 12, characterized in that the vehicle (50) has a temperature sensor (20), brake pad sensor (22), tire sensor (21) and / or speed sensor (23) arranged on a friction brake unit (10) and / or on a wheel (11) of the vehicle (50).

14. Vehicle (50) according to claim 12 or 13, characterized in that the vehicle (50) has a suspension system (25) with a bellows (26b) and a bellows pressure sensor (26).

15. Vehicle (50) according to one of claims 12 to 14, characterized in that the vehicle (50) is designed as a trailer vehicle (51).

16. Computer program (33) comprising machine-readable instructions (34) which, when the instructions (34) are executed by a computing unit (31), cause the computing unit (31) to carry out the method (100) according to one of claims 1 to 10.

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