Method and brake system for actuating a brake actuator in order to reduce tensioning of a vehicle

Abstract

In a method for actuating a brake actuator (8) in a braked stationary vehicle (100), a state variable (Z1, Z2, Z3) which characterizes the loading state of the vehicle (100) is monitored, and a tensioning in the vehicle (100) produced by a change in level is detected. The state variable (Z1, Z2, Z3) is compared with a defined value range, and the brake actuator (8) is initiated in response to the detection of a tensioning. If the state variable (Z1, Z2, Z3) is to be assigned to the defined value range, a first target braking is actuated and / or if the state variable (Z1, Z2, Z3) is not to be assigned to the defined value range, a second target braking is actuated. The invention additionally relates to a brake system and to a vehicle.

Description

[0001] METHOD AND BRAKING SYSTEM FOR CONTROLLING A BRAKE ACTUATOR TO RELIEVE TENSION IN A VEHICLE

[0002] The present invention relates to a method for controlling at least one brake actuator by a braking system in a braked, stationary vehicle with the aim of reducing a tension in the vehicle caused by a change in level.

[0003] Such a vehicle can, in particular, be a commercial vehicle. Vehicles or commercial vehicles of the type mentioned above are equipped with a suspension to cushion a vehicle body. Such a suspension can, for example, be a mechanical suspension or a pneumatic suspension. Due to the suspension, the height of the vehicle body above the wheels or axles is not constant. When loading, the height decreases, and when unloading, the height increases. The change in the height of the vehicle body relative to the wheels or axles is also referred to as level change. Particularly in vehicles with pneumatic suspension, it is possible to actively adjust the height using pneumatic level control, for example by manually or automatically actuating the pneumatic suspension. This also applies to trailer vehicles and truck-trailer combinations.

[0004] In many vehicles, the wheel axles are mounted on longitudinally aligned axle swing arms or trailing arms. With every change in level, caused by a change in the height of an axle, the affected axle swing arm moves on a fraction of a circular path. This can result in a change in the wheelbase, i.e. a change in the distance between the rear and front wheels, depending on the position of the axle swing arm on its circular path. The changed wheelbase leads to tension, whereby the wheels must turn through a small angle to compensate for the tension on at least one axle. Loading vehicles typically takes place with the vehicle braked and stationary. In this case, the wheels of each of the vehicle's axles are preferably braked. The axles or wheels are braked by a brake actuator which is designed to provide a braking function, preferably a service braking function or a parking braking function.

[0005] For example, to provide a parking brake function, the brake actuator is applied in such a way that a number of brake pads can be freely pressed mechanically against a corresponding brake disc or brake drum by spring force, without the brake actuator applying a counteracting force. Braking force can also be applied by applying the brake actuator itself, for example, electrically.

[0006] By providing a braking function through the brake actuator, the wheels are no longer rotatable, meaning a change in wheelbase cannot be compensated for. This results in varying degrees of tension in the vehicle, depending on the respective level change.

[0007] The problem of distortion also occurs in a truck / trailer combination, i.e., a combination of tractor and semitrailer. The relevant factor is the wheelbase between the rear wheels of the tractor and the wheels of the semitrailer. Finally, the described distortion can occur in any vehicle or truck / trailer combination where a change in level results in a change in the wheelbase, for example, in a combination of a tractor and a drawbar trailer.

[0008] EP 1 800 916 B1 discloses a method for compensating for the described tension. If the level of the vehicle body relative to the wheels changes during or after the change, the tension is automatically reduced by alternating, complete release of the brake actuator. A disadvantage of this known method is the relatively high air consumption due to the complete release and re-locking of the brake actuator.

[0009] DE 1002014 012 549 describes a method that solves the problem of increased air consumption by releasing the brake actuators on both sides while maintaining a minimum deceleration. However, this minimum deceleration is not tailored to the actual load conditions of the vehicle. The maintained minimum deceleration is therefore often oversized to comply with legal requirements. As a result, severe tensions may not be completely relieved because the maintained minimum deceleration is too high to ensure sufficient wheel rotation.

[0010] The object of the present invention is therefore to overcome at least one of the disadvantages known from the prior art. In particular, the object of the present invention is to more effectively, and preferably completely, eliminate the tensions generated by a change in vehicle level.

[0011] The invention solves the underlying problem by a method according to claim 1, a braking system according to claim 15 and a vehicle according to claim 18.

[0012] With regard to a method of the type mentioned at the outset for controlling a brake actuator - wherein a plurality of brake actuators can be controlled - the invention proposes that the method comprise the following steps: a) monitoring a state variable that characterizes a load state of the vehicle - wherein a plurality of state variables can be monitored -, b) detecting a tension in the vehicle generated by a change in level, c) comparing the state variable with a predefined value range and d) releasing the brake actuator in response to the detection of a tension, wherein in the event that the state variable can be assigned to the predefined value range, a first target braking is controlled, and / or if the state variable cannot be assigned to the predefined value range, a second target braking is controlled.

[0013] For the purposes of the invention, a load condition is any condition of the vehicle or a truck / trailer combination that has a direct or at least indirect influence on the required braking force. A state variable in this context is a directly or indirectly measurable value that characterizes the load condition and thus also directly or at least indirectly allows a conclusion to be drawn about the required braking force. Target braking, in this case, is understood to mean a reduced braking compared to the full braking of the vehicle, expressed as a percentage. A level change, for the purposes of the invention, is understood to mean both an active and a passive level change.

[0014] In the sense of the invention, a state variable is not to be assigned to a predefined value range in the event that it lies outside the value range or cannot be clearly determined.

[0015] In a stationary vehicle with brakes applied, it is necessary to temporarily reduce the braking force to relieve tension, thus allowing at least one axle of the vehicle to rotate. Releasing the brake actuator in this context refers to reducing the braking force by controlling the brake actuator accordingly.

[0016] In the method according to the invention, in addition to detecting tension in the vehicle, additional information, namely the current state variable, is monitored and processed. This enables precise control of the brake actuator, taking into account the current load state of the vehicle. Thus, when releasing the brake actuator, it is possible to react to varying load conditions. By releasing the brake actuator while controlling a second predefined target deceleration depending on the detected state variable, the method according to the invention also takes into account situations in which the load state does not allow the target deceleration to be determined as a function of the state variable.

[0017] The initial target deceleration can be defined as a function of the state variable. This allows for more precise and load-dependent release of the brake actuator as an immediate response to changing vehicle load conditions. Safety-related over-dimensioning of the deceleration due to a lack of precise knowledge of the vehicle's load condition is thus no longer necessary.

[0018] It is preferred that step b) be performed before step c). Further preferably, steps a) to d) are performed successively. Thus, a comparison of the continuously monitored state variable with the predefined value range only takes place if stress is detected in step b).

[0019] According to one embodiment, at least step a), in particular step a) and step b), is carried out continuously and steps c) and d) are carried out in the event that a tension is detected in step b).

[0020] According to a further embodiment, the state variable is a first state variable which characterizes a first load state and which is compared in step c) with a first predefined value range, wherein in step a) a second state variable which characterizes a second load state of the vehicle is further monitored.

[0021] In particular, the second state variable can be compared with a second predefined value range in step c). Thus, different value ranges are taken into account and the brake actuator is controlled depending on two different state variables and corresponding value ranges.

[0022] According to an alternative, the first state variable and a second state variable characterize the load state, and both state variables are compared with the first predefined value range in step c). This allows for better monitoring of the vehicle's load state and, in particular, allows interactions between the state variables to be taken into account.

[0023] Furthermore, in step d), the first target deceleration can be controlled in the event that the first state variable can be assigned to the first predefined value range and the second target deceleration to the second predefined value range, and in step d), a third target deceleration can be controlled in the event that the second state variable (Z2) cannot be assigned to the second predefined value range. In this case, the first state variable is preferably assigned to the first value range. Thus, the influence of both state variables on the required braking force and thus the target deceleration to be controlled is taken into account. In this case, the invention advantageously recognizes that in situations in which at least the first state variable can no longer be assigned to the first value range, a second target deceleration different from the first target deceleration must be controlled.In addition, the invention recognizes that in situations in which at least the second state variable cannot be assigned to the second value range, this individual load state can also be taken into account by controlling a third predefined target deceleration, which is different from the first target deceleration and the second target deceleration. In the event that neither the first state variable nor the second state variable can be assigned to the predefined value range, a fourth target deceleration can be controlled. Thus, the safety of the vehicle is increased by the individual adjustment to the different load states and, at the same time, tensions can be effectively reduced. In particular, at least one load state is a position state and the state variable is an angle of inclination of the vehicle relative to the horizontal.In this case, a positional state is understood to mean the inclination of the vehicle relative to the horizontal, which is caused, for example, by a gradient in the road.

[0024] Furthermore, the inclination angle can be monitored by sensing the vehicle's acceleration via a sensor unit. Depending on the current position, downhill forces act on the vehicle, which directly influence the required braking force. The braking force must overcome the downhill force, which is a function of the inclination angle. Thus, by monitoring the vehicle's acceleration, the inclination angle can be determined, which can then be continuously monitored. The brake actuator can then be controlled depending on the inclination angle, and the inclination angle can be compared with the predefined value range, particularly when tension is detected, and used, if necessary, to determine the target braking rate.

[0025] According to a further development of the method, the predefined value range includes inclination angles in a range of |0° < a < | ± 90°|, in particular from 0° < a < | ± 12°|. Furthermore, the predefined value range can include inclination angles in a range of 0° < a < | ± 7°| or | ± 7°| < a < | ± 10°|.

[0026] In particular, the first target deceleration can be defined as the quotient of the braking force m ■ g ■ sin a and the weight force f = m ■ g in % and the second target deceleration can assume a value < 1 %. Thus, the first f

[0027] Target braking is defined as ^-^ and a first target braking is determined as a function of the angle of inclination for a value range of 0° < a < | ± 90°|, in particular a value range of 0° < a < | ± 12°|. If the state variable lies outside this value range or cannot be determined, it cannot be assigned to it. In this case, the brake actuator is controlled with a second target braking. This is the case, for example, with a vehicle stationary on a level surface, with the angle of inclination corresponding to 0°. In this case, no downhill forces act on the vehicle and the second target braking can assume a discrete value < 1% or the brake actuator can be completely released. In this way, the vehicle's tension is completely removed quickly and efficiently, since the wheels are only braked with a second target braking of < 1%.

[0028] According to a further embodiment, at least one load condition is a loading condition, and the state variable is a pressure that characterizes the loading condition of the vehicle. In this case, a loading condition of the vehicle is understood to mean the weight and / or the distribution of the load and the associated distribution of the axle load of the vehicle.

[0029] The level of the vehicle or vehicle body can be actively controlled by controlling the pressure in a pressure-regulated vehicle suspension. This is used, for example, to react to changes in the loading conditions. At the same time, a changed arrangement or weight of the load leads to a change in the axle load distribution and thus to a change in the pressure in the suspension. Monitoring the pressure thus allows conclusions to be drawn about the vehicle's loading condition. By monitoring the pressure, a more precise release of the brake actuator is possible in the method according to the invention. However, the weight or distribution of the load, for example when loading an empty vehicle, may not be determinable by monitoring the pressure. When loading the vehicle, the vehicle body may be lowered by the suspension.In this case, the pressure cannot be clearly assigned to a predefined value range, so a second predefined target deceleration is triggered. This can, for example, correspond to the so-called loading characteristic, i.e., the deceleration required for a fully loaded vehicle. It is possible that the loading condition is monitored by sensing the air bellows pressure of a pneumatic suspension or the hydraulic pressure of a vehicle's hydraulic suspension using a sensor unit.

[0030] A pneumatic suspension or air suspension system of a vehicle comprises an air supply and a bellows connection for connecting one or more air bellows to the air supply, as well as a valve, in particular a solenoid valve, for blocking or opening a connection between the air supply and the bellows connection. The pneumatic suspension or air suspension system can comprise several valves. The level of the vehicle or vehicle body can be actively controlled by controlling the pressure in the air bellows. In addition to this active level change or level control, a passive control of the level of the vehicle body above the axles can take place through the vehicle load. As a result of this passive level change due to a changed arrangement or changed weight of the load, as well as with an active level change, the pressure in the air bellows changes, whereby the pressure in the air bellows is monitored by the sensor unit.To control the brake actuator of an air-sprung vehicle, sensing the air spring bellows pressure allows conclusions to be drawn about a change in the weight of the load and, in particular, its distribution. Thus, the sensor unit is designed to detect tension caused by both active and passive level changes.

[0031] In particular, the predefined value range in a pneumatic suspension or air suspension system can include pressures in a range of 0.1 bar < p < 10 bar, in particular in a range of 1 bar < p < 6 bar. Furthermore, the second target deceleration can correspond to the maximum target deceleration for a fully loaded vehicle.

[0032] In the case of hydraulic suspension of the vehicle body, the sensor unit also monitors the hydraulic pressure in the method according to the invention. Differences in the hydraulic pressure are used to monitor passive level changes caused by changes in the position or weight of the vehicle body's load. Furthermore, the pressure for an active level change can be actively controlled. A change in the hydraulic pressure allows conclusions to be drawn about a change in the vehicle weight or the distribution of the vehicle's load. Thus, the first target deceleration can be determined depending on this state variable.

[0033] In particular, the predefined value range of a hydraulic suspension can include pressures in a range of 2.5 bar < p < 200 bar. Furthermore, the second target deceleration can correspond to the maximum target deceleration for a fully loaded vehicle.

[0034] In particular, at least one load condition can be a loading condition, and the state variable can be a deflection of a mechanical suspension, which characterizes the loading condition of the vehicle. In the case of mechanical suspension of the vehicle or the vehicle body, the vehicle body, or in particular an axle assembly, deflects when the weight or distribution of the load of the vehicle or the vehicle body changes. Monitoring the change in this deflection by a sensor unit thus enables the provision of a suitable state variable, depending on which a target deceleration can be controlled by the brake actuator.

[0035] Furthermore, in step b), a tension of the vehicle can be detected if the following conditions are met: a) the vehicle is stationary and b) the vehicle is braked and c) a limit value for a level change is exceeded or undershot.

[0036] Whether the vehicle is braked can be determined from the status of at least one brake actuator, and in the case of an electropneumatically actuated brake actuator, in particular also from the brake control pressure. In particular, the brake actuators can be controlled by a control unit of a braking system to activate a parking brake function, and the activation can be detected to detect a braked state of the vehicle. The level change results from the signals of a displacement sensor assigned to an axle. The level change is calculated as the difference between a currently detected level and the neutral position, whereby the neutral position is detected and stored when the service brake or parking brake is released. The level change should preferably be at least + / - 20 mm compared to an initial position. The initial position is also referred to below as the neutral position.

[0037] In particular, the conditions are queried successively one after the other and the subsequent condition is only queried when the previous condition is met.

[0038] In particular, the vehicle has at least one axle, each axle being assigned two brake actuators that are controlled simultaneously in step d). It should be understood that simultaneous control of the two brake actuators is to be understood as temporal and also includes control with different control pressures and target decelerations.

[0039] The invention has been described above in a first aspect with respect to a method.

[0040] The invention achieves the object mentioned at the outset in a second aspect by means of a braking system, in particular an electronically controllable pneumatic braking system, for a vehicle for controlling a brake actuator, comprising a sensor unit for monitoring a state variable that characterizes a load state of the vehicle - wherein the sensor unit can be configured to monitor a plurality of state variables -, a displacement sensor for detecting a tension in the vehicle generated by a change in level, and a control unit that is connected in a signal-conducting manner to the sensor unit and the displacement sensor and is configured to release the brake actuator in response to the detection of a tension and, in the event that the state variable can be assigned to the predefined value range, to control a first target braking, and / or, if the state variable cannot be assigned to the predefined value range, to control a second target braking.

[0041] In particular, the first target deceleration can be defined as a function of the state variable.

[0042] Because the control unit is signal-conductingly connected to the sensor unit and the displacement sensor and is configured to release the brake actuator as a function of the monitored state variable by controlling a first target deceleration or a second target deceleration, the braking system according to the invention incorporates the advantages described with respect to the method according to the first aspect of the invention. Possible embodiments with respect to the first aspect of the invention are also possible embodiments with respect to the second aspect of the invention, and vice versa.

[0043] In particular, the braking system can be configured to carry out a method according to the first aspect of the invention.

[0044] The braking system may be an electronically controllable pneumatic braking system and the braking actuator may be an electronically controlled pneumatic braking actuator.

[0045] The electropneumatic braking system can comprise a, particularly single-circuit, electropneumatic system component with the control unit, an axle modulator assigned to one of the axles, a brake signal transmitter, and two ABS valves assigned to one of the axles. Such a control unit is also referred to as a central module. The brake actuator can comprise a brake cylinder, and the axle modulator can be connected to the control unit via a signal-conducting connection. The control unit can be configured to control the axle modulator depending on the signal from the brake signal transmitter, so that the axle modulator regulates the brake cylinder pressure on both sides of one or two axles.

[0046] If the vehicle is coupled to a trailer, the electropneumatic system component also includes an electropneumatic trailer control valve. Electrical control and monitoring are preferably carried out by the control unit.

[0047] The brake actuator can be configured to provide a service braking function, wherein the braking by the service braking function of a braked vehicle is reduced by releasing the brake actuator by controlling a first target braking or the second target braking.

[0048] The braking system can be an electric braking system, and the brake actuator can be an electric brake actuator, such as an actuator. An electric brake actuator reduces response times.

[0049] Furthermore, the brake actuator can be configured to provide a parking brake function, wherein the deceleration by the parking brake function of a braked vehicle is reduced by releasing the brake actuator by controlling a first target deceleration or the second target deceleration. Such a parking brake function, which is automatically activated when the vehicle is stationary, is also referred to as a parking brake function. Furthermore, at least one load state can be a position state and at least one state variable can be an angle of inclination of the vehicle relative to the horizontal, wherein the sensor unit has an acceleration sensor for monitoring the angle of inclination. An acceleration sensor enables the monitoring of the longitudinal acceleration acting on the vehicle, which depends on the slope force and thus the angle of inclination of the vehicle relative to the horizontal.By monitoring the acceleration of the stationary vehicle using an acceleration sensor, the vehicle's inclination angle can be reliably monitored.

[0050] According to a further embodiment, at least one load condition is a loading condition and at least one state variable is a suspension pressure, and wherein the sensor unit comprises a pressure sensor for monitoring the pressure. In vehicles with pneumatic suspension, the pressure sensor is a bellows pressure sensor, also referred to as an axle load sensor. By detecting the bellows pressure in one or more air spring bellows, this enables the axle loads to be determined and thus the vehicle's loading condition to be reliably monitored. It is only known to use this signal to adapt the braking forces to different loading conditions. The inventors also recognized that monitoring the pressure in a braked, stationary vehicle can also advantageously serve to release the brake actuators to reduce tension by triggering a suitable target braking.The target braking is selected and controlled accordingly by a control-technical case differentiation of the loading condition, i.e. by comparing the bellows pressure with a predefined value range.

[0051] In the case of a hydraulically sprung vehicle, a pressure sensor for monitoring the hydraulic pressure of the suspension also enables reliable monitoring of the load condition. It is also possible for at least one load condition to be a load condition and at least one state variable to be a spring deflection of a mechanical suspension, in particular an axle assembly. The sensor unit has, in particular, a travel sensor for monitoring the spring deflection. In this application, the travel sensor delivers a signal proportional to the spring deflection and thus, in particular, to the current axle load. Monitoring the spring deflection enables simple and reliable monitoring of the load condition in mechanically sprung vehicles.

[0052] The invention achieves the aforementioned object in a third aspect by a vehicle, preferably a commercial vehicle, with at least one axle suspended on trailing arms or semi-trailing arms and a braking system according to the second aspect of the invention for controlling a brake actuator assigned to the axle. The vehicle according to the invention with a braking system according to the second aspect incorporates the advantages described with reference to the first and second aspects, respectively. Advantages and possible embodiments of the first and second aspects of the invention are likewise advantages and possible embodiments with reference to the third aspect of the invention, and vice versa.

[0053] In particular, the vehicle can be a semitrailer truck, in particular an air-sprung semitrailer truck, comprising a tractor unit with at least one axle suspended by trailing arms or semi-trailer arms, and a semitrailer connectable to the tractor unit with at least one axle suspended by trailing arms or semi-trailer arms. The braking system can be configured to control the brake actuator of the tractor unit and / or the semitrailer.

[0054] According to an alternative embodiment, the vehicle is a tractor with an axle suspended on trailing arms or semi-trailing arms and a trailer connectable to the tractor, with an axle suspended on trailing arms or semi-trailing arms and a dedicated brake actuator associated with the axle, with an electropneumatic trailer control valve. The brake actuator of the trailer, in particular the trailer control valve, can be configured for control in a method according to the first aspect of the invention, wherein the control can be carried out in particular by the control unit of the tractor.

[0055] According to a fourth aspect, the invention further relates to the use of an acceleration sensor in a method for controlling a brake actuator according to the first aspect of the invention, wherein the load state is a positional state and the state variable is an inclination angle of the vehicle relative to the horizontal, and wherein the acceleration sensor is configured to monitor the state variable. Advantages and possible embodiments of the first aspect of the invention are also advantages and possible embodiments with respect to the fourth aspect of the invention, and vice versa.

[0056] Embodiments of the invention will now be described below with reference to the drawings. These are not necessarily intended to represent the embodiments to scale; rather, the drawings are schematic and / or slightly distorted where this is useful for explanation. With regard to additions to the teachings immediately apparent from the drawings, reference is made to the relevant prior art. It should be noted that numerous modifications and changes to the form and detail of an embodiment can be made without deviating from the general idea of ​​the invention. The features of the invention disclosed in the description, in the drawings and in the claims can be essential for the further development of the invention, both individually and in any combination.Furthermore, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. The general idea of ​​the invention is not limited to the exact form or detail of the preferred embodiments shown and described below, or limited to an object that would be more limited than the object claimed in the claims. For specified dimensioning ranges, values ​​within the stated limits are also intended to be disclosed as limit values ​​and to be used and claimed as desired. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar functions.

[0057] Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings, which show:

[0058] Fig. 1 a tractor unit with a semitrailer, the semitrailer being lowered, schematically in a side view,

[0059] Fig. 2 a tractor unit with a semi-trailer, with the semi-trailer raised, schematically in a side view,

[0060] Fig. 3 shows a tractor-trailer combination with a semi-trailer, the tractor-trailer combination standing on a sloping surface, schematically in a side view,

[0061] Fig. 4 shows the truck combination according to Figs. 1 to 3 more schematically in a plan view, and

[0062] Fig. 5 shows a second embodiment of a truck combination more schematically in a plan view.

[0063] Figures 1 to 3 show a vehicle 100. The vehicle 100 is in this case a semitrailer truck, which here consists of a tractor 11 with a fifth wheel plate 12 and a semitrailer 13 with a kingpin 14.

[0064] The tractor 11 has a front axle 15 and a rear axle 16. The semi-trailer 13 has an axle 17 which is mounted on an axle swing arm 18. The axle swing arm 18 can be pivoted about a bearing point 19 and forms a trailing longitudinal control arm for the axle 17. The height of the axle 17 is adjustable by an air bellows 20 which acts on the axle swing arm 18 opposite the bearing point 19. In Fig. 1, the air bellows 20 is minimally inflated, while Fig. 2 and Fig. 3 show a maximally inflated air bellows 20. Accordingly, the level of the semi-trailer 13 in Fig. 1 is significantly lower than in Fig. 2 and Fig. 3, respectively. The term level here refers to the distance between the axle 17 and the vehicle body 21 of the semi-trailer 13.

[0065] The semitrailer 100 has an electropneumatic braking system 10 and a suspension 3. In the illustrated embodiment, the suspension 3 is an electronically controlled pneumatic suspension. This enables automatic level control during loading as well as targeted adjustment of the height of the vehicle body 21 to a loading ramp.

[0066] For example, tension occurs between the states shown in Fig. 1 and Fig. 2 or Fig. 3. In Fig. 1, the level of the trailer 13 is lowered for driving. The wheelbase, or here the distance between the axle 17 and the kingpin 14, is represented by a double arrow a.

[0067] In Fig. 2 and Fig. 3, the level of the semi-trailer 13 is raised. Accordingly, the axle rocker 18 is pivoted downward. This creates a new, shorter distance, as indicated by the double arrow b (cf. Fig. 2), between the axle 17 and the kingpin 14. When the wheels 23, 24 of the rear axle 16 and the axle 17 are braked, this results in severe tension in the semi-trailer 13, which may be so pronounced that, based on Fig. 1, the state according to Fig. 2 or Fig. 3 is not achievable. In the meantime, it is necessary to relieve the tension by at least slightly releasing the parking brake 25 (cf. Figs. 4 and 5) by controlling the respective brake actuator 8 of the electro-pneumatic braking system 10 via the braking system 1.

[0068] Fig. 4 shows the vehicle floor 22 of the semitrailer truck 100 according to Figures 1 to 3 in detail. The electropneumatic braking system 10 shown in detail in Fig. 4 comprises an electronically controllable pneumatic braking system 1 in conjunction with a number of electronically controlled pneumatic brake actuators 8 and a compressed air supply (not shown) for the brake actuators 8, with at least two brake actuators 8 being assigned to the rear axle 17.

[0069] The braking system 1 is configured to detect a tensioning of the semitrailer 100 and to release the brake actuator 8 of the electropneumatic braking system 10 to reduce the tension by controlling a target braking.

[0070] The braking system 1 comprises, in particular, a single-circuit electropneumatic system component with the control unit 6, an axle modulator 25 assigned to one of the axles 17, a brake value sensor (not shown), and two ABS valves (not shown) assigned to one of the axles 17. The axle modulator 25 is thus connected to the control unit 6 in a signal-conducting manner. Such a control unit 6 is also referred to as a central module. The brake actuators 8 preferably each comprise a brake cylinder (not shown).

[0071] The control unit 6 is configured to control the axle modulator 25 depending on the signal from the brake value sensor, so that the axle modulator 25 regulates in particular the brake cylinder pressure on both sides of the rear axle 17.

[0072] The braking system 1 further comprises a sensor unit 5 and wheel speed sensors 7, which are connected to the control unit 6.

[0073] The pneumatic suspension 3 is electronically controlled and includes a travel sensor 4, which detects the actual level of the axle 17 and changes in the level. The travel sensor 4 is preferably connected to the braking system 1, preferably to the control unit 6, in a signal-conducting manner. The control unit 6 preferably continuously evaluates the signals from the travel sensor 4, as well as the signals from the wheel speed sensors 7.

[0074] The control unit 6 also receives information about the activation of a braking function, preferably a parking brake function or a service brake function. The control unit 6 preferably stores the current level (actual level) of axle 17 at regular intervals or under certain conditions, namely as long as or as soon as the wheels 24 of axle 17 are not braked. This stored actual level is referred to as the neutral position.

[0075] Starting from the neutral position, the braking system 1, preferably the control unit 6, is configured to detect tension by means of the signals from the travel sensor 4.

[0076] In the present case, the braking system 1 of the semi-trailer 13 is equipped with an additional function for reducing the tension, which essentially lies in the function and software of the control unit 6. This detects tension in the semi-trailer 13 in the manner described above. Furthermore, the braking system 1 monitors at least one state variable Zi, Z2 via the sensor unit 5, wherein the braking system 1 is configured with the control unit 6 to release the brake actuators 8 depending on the monitored state variable Z1, Z2 in the event that tension is detected. To reduce the detected tension by releasing the brake actuators 8, the braking system 1 and in particular the control unit 6 triggers a first target braking or second target braking by the brake actuator 8, in particular by correspondingly controlling the respective brake cylinder (not shown) or any brake valves (not shown).This additional function of the braking system 1 makes it possible to control the brake actuator 8 of the semi-trailer 100 as needed in the various load states shown in Figs. 2 and 3. The state variable Zi monitored by the sensor unit 5 is, in particular, an inclination angle α, and the load state characterized by the inclination angle α is a positional state of the semi-trailer 100. The sensor unit 5 comprises an acceleration sensor 5.1 for monitoring the inclination angle α.

[0077] In Fig. 2, the semi-trailer 100 is on a level surface with an inclination angle a = 0°. In Fig. 3, however, the semi-trailer 100 is on a slope with an inclination angle a = 10°. These two positions of the semi-trailer 100, characterized by the angle a, each require a coordinated minimum deceleration to prevent the semi-trailer 100 from rolling away unintentionally when the brake actuators 8 are released.

[0078] The control unit 6 is also connected to an electronic system of the tractor 11 (not shown in detail) via a standardized data connection, in this case a CAN bus system 9. The function, components, and interaction of these systems are generally known. Only the components relevant to understanding the invention are shown in the figures.

[0079] The release of brake actuator 8 is intended only for a short time. After the tension is released, the brake pressure is increased back to the original value. The period during which the reduction in braking effect lasts is approximately 0.2 to 2 seconds. Depending on the vehicle geometry and the properties of the systems involved, this period may also be longer.

[0080] In the following, the method according to the invention is described by way of example with reference to the load conditions shown in Figures 1 to 3, as well as the execution of the method in a braking system 1 for a vehicle 100 according to the embodiment shown in Figure 4.

[0081] In the state shown in Fig. 2, the braking system 1 (cf. Fig. 4) monitors, in particular continuously, the inclination angle α by means of the acceleration sensor 5.1. This inclination angle α is either continuously compared with a predefined value range of 0° < α < 90°, in particular with a predefined value range of 0° < α < 12°, by the control unit 6 or only in the event that a tension is detected by the displacement sensor 4. In response to a detected tension, the brake actuators 8 are released by the control unit 6 triggering a second target braking, since the inclination angle α = 0° and thus lies outside the predefined value range.

[0082] In the embodiment shown in Fig. 3, the semitrailer 100 is on a slope inclined by an angle a = 10°. In this case, the braking system 1 (cf. Fig. 4) and in particular the control unit 6 will, in response to a detected tension, release the brake actuators 8 by controlling a first target deceleration by the control unit 6, since the angle of inclination a = 10° and thus lies within the predefined value range. The first target deceleration can be defined, in particular, as a function of the state variable Zi, i.e., the angle of inclination a. The first target deceleration is determined as the quotient of the necessary braking force ö(c ) = m ■ g ■ sin a and the weight force f (g = m - g. This results in a first target braking of 17.4% at an inclination angle a = 10°. Thus, the brake actuator 8 can be released by the electric braking system 1 with the control unit 6 exactly as a function of the detected state variable Zi, in this case the inclination angle.

[0083] Furthermore, the sensor unit 5 can comprise another sensor, in particular a pressure sensor 5.2, in addition to the acceleration sensor 5.1. In this case, two load states, namely a position state and a load state, are taken into account when controlling the brake actuators 8. The braking system 1 is configured to monitor a first state variable Zi, in this case an inclination angle α, by means of the acceleration sensor 5.1 of the sensor unit 5 and further to monitor a second state variable Z2, for example an air spring bellows pressure of the air spring bellows 20 (cf. Figs. 1 to 3), by means of the pressure sensor 5.2 of the sensor unit 5.

[0084] In this case, the braking system 1 is further configured to release the brake actuators 8 as a function of the first monitored state variable Zi and the second monitored state variable Z2 by controlling a first target braking in the event that the first state variable Zi, i.e. the inclination angle a, corresponds to the first predefined value range of 0° < a < + / -90 0 , in particular of 0° < a < + — 12°, and the second target braking, i.e. the air bellows pressure, is to be assigned to the second predefined value range of 0.1 bar < p < 10 bar, controlling a second target braking in the event that the first state variable Zi cannot be assigned to the second predefined value range, and controlling a third target braking in the event that the second state variable Z2 cannot be assigned to the second predefined value range.

[0085] The second target deceleration can be, in particular, < 2% and > 0%, in particular < 1% and > 0%. In this case, the semi-trailer 100 is on level ground.

[0086] The air spring bellows pressure cannot be clearly determined, especially when loading an empty semitrailer 100 with the trailer 13 lowered, and thus cannot be assigned to the second predefined value range. In this case, the third target deceleration is activated, which is, in particular, a value corresponding to the so-called loading characteristic curve. This is a deceleration that must be applied in the case of a fully loaded semitrailer 100.

[0087] Fig. 5 shows a further embodiment of the vehicle 100, which in this case is a semi-trailer truck. The vehicle floor 22 of the semi-trailer truck 100 with the electropneumatic braking system 10 is shown in detail. The vehicle 100 shown in Figure 5 differs from the embodiment shown in Figures 1 to 4, firstly, in the suspension 3, which is designed as a mechanical suspension.

[0088] The electropneumatic brake system 10 comprises, in a known manner, an electronically controllable pneumatic brake system 1 in conjunction with a number of electronically controlled pneumatic brake actuators 8 and a compressed air supply (not shown) for the brake actuators 8, with at least two brake actuators 8 being assigned to the rear axle 17. The electronically controllable pneumatic brake system 1 comprises the control unit 6, with the axle modulator 25 being integrated into the control unit 6 in this exemplary embodiment.

[0089] The load state monitored in this exemplary embodiment is a loading state, and the state variable Z3 is a spring deflection of the mechanical suspension 3. In the mechanical suspension 3 of the vehicle 100 or the vehicle body 21, the vehicle 100 or the vehicle body deflects when the weight or distribution of the load of the vehicle 100 or the vehicle body changes, so that the loading state is characterized by the spring deflection Z3.

[0090] To reduce tension in the braked, stationary vehicle 100, the braking system 1 comprises, in a known manner, a braking system 1 having a control unit 6 with an integrated axle modulator, to which, among other things, wheel speed sensors 7 are connected for detecting tension in the vehicle 100 caused by a change in level. The braking system 1 can be controlled by means of the braking system 1. Furthermore, the braking system 1 comprises a sensor unit 5 with at least one height sensor 5.3 for monitoring the spring deflection Z3, wherein the brake actuator 8 controls a target deceleration depending on the spring deflection Zs. Within the meaning of the invention, the sensor unit 5 can also have a combination of the sensors shown in Figures 4 and 5 and an acceleration sensor 5.1 for monitoring the first state variable Zi, a pressure sensor 5.2 for monitoring the second state variable Z2, and a height sensor 5.3 for monitoring the third state variable Z3, wherein the brake system 1 can be configured to release the brake actuator as a function of the first state variable Z1, the state variable Z2 and the third state variable Zs.

[0091] List of reference symbols (part of the description):

[0092] 1 braking system

[0093] 3 Suspension

[0094] 4 displacement sensor

[0095] 5 Sensor unit

[0096] 5.1 Acceleration sensor

[0097] 5.2 Pressure sensor

[0098] 5.3 Altitude sensor

[0099] 6 Control unit

[0100] 7 Wheel speed sensor

[0101] 8 Brake actuator

[0102] 9 CAN bus system

[0103] 10 electropneumatic braking system

[0104] 11 tractor

[0105] 12 saddle plate

[0106] 13 trailers

[0107] 14 kingpins

[0108] 15 front axle

[0109] 16 Rear axle

[0110] 17 Axis

[0111] 18 axle swing

[0112] 19 bearing point

[0113] 20 air spring bellows

[0114] 21 Vehicle body

[0115] 22 Vehicle floor

[0116] 23 wheels

[0117] 24 wheels

[0118] 25 Axle modulator 100 Vehicle a Wheelbase b Wheelbase a Tilt angle Zi first state variable

[0119] Z2 second state variable

[0120] Z3 third state variable

Claims

Patent claims 1. A method for controlling a brake actuator (8) in a braked, stationary vehicle (100), comprising the steps of: a) monitoring a state variable (Z1, Z2, Z3) which characterizes a load state of the vehicle (100), b) detecting a tension in the vehicle (100) generated by a change in level, c) comparing the state variable (Z1, Z2, Z3) with a predefined value range and d) releasing the brake actuator (8) in response to the detection of a tension, wherein in the event that the state variable (Z1, Z2, Z3) can be assigned to the predefined value range, a first target braking is controlled and in the event that the state variable (Z1, Z2, Z3) cannot be assigned to the predefined value range, a second target braking is controlled.

2. Method according to claim 1, characterized in that the first target deceleration is defined as a function of the state variable (Z1, Z2, Z3) and the second target deceleration is a discrete value.

3. The method according to claim 1 or 2, characterized in that the state variable is a first state variable (Z1) which characterizes a first load state and which is compared in step c) with a first predefined value range, wherein furthermore at least one second state variable (Z2) is monitored which characterizes a second load state of the vehicle (100) and which is compared in step c) with a second predefined value range.

4. Method according to claim 3, characterized in that in step d) the first target deceleration is controlled in the event that the first state variable (Zi) is to be assigned to the first predefined value range and the second target deceleration (Z2) is to be assigned to the second predefined value range, and in that in step d) a third target deceleration is controlled in the event that the second state variable (Z2) is not to be assigned to the second predefined value range.

5. Method according to one of the preceding claims, characterized in that a load state is a position state and a state variable (Z1) is an angle of inclination (α) of the vehicle (100) relative to the horizontal.

6. The method according to claim 5, characterized in that the angle of inclination (a) is monitored by sensing an acceleration of the vehicle (100) by a sensor unit (5).

7. Method according to one of claims 5 or 6, characterized in that the predefined value range comprises inclination angles (a) in the range 0° < a < | ± 90°| , in particular 0° < a < | ± 12°|, in particular 0° < a < | ± 7°| or | ± 7°| < a < | ± 10°|.

8. Method according to one of claims 5 to 7, wherein the first target braking is the quotient of the braking force / h (a) = m ■ g - sin a and the weight force f (g = m - g is defined in percent, and the second target deceleration takes a value < 1 %.

9. Method according to one of the preceding claims, characterized in that a load state is a loading state and a state variable (Z2) is a pressure of a suspension (3).

10. The method according to claim 9, characterized in that the loading state is monitored by sensing an air bellows pressure of a pneumatic suspension (3) or a hydraulic pressure of a hydraulic suspension by a sensor unit (5).

11. Method according to one of claims 9 or 10, characterized in that the predefined value range comprises pressures in a range 0.1 bar < p < 200 bar, wherein the suspension (3) is in particular a pneumatic suspension and the predefined value range comprises pressures in a range 0.1 bar < p < 10 bar, or the suspension (3) is in particular a hydraulic suspension and the predefined value range comprises pressures in a range 2.5 bar < p < 200 bar, and wherein the second target braking corresponds to the maximum target braking when the vehicle (100) is fully loaded.

12. Method according to one of the preceding claims, characterized in that a load state is a loading state and a state variable (Z3) is a compression travel of a mechanical suspension (3).

13. Method according to one of the preceding claims, characterized in that in step b) a tension of the vehicle (100) is detected in the event that the following conditions are met: i) the vehicle (100) is stationary, and ii) the vehicle (100) is braked, and iii) a limit value of a level change is exceeded or undershot.

14. Method according to one of the preceding claims, characterized in that the vehicle (100) has at least one axle (15, 16, 17), and wherein two brake actuators (8) are assigned to each axle (15, 16, 17), which are controlled simultaneously in step d).

15. Braking system (1), in particular an electronically controllable pneumatic braking system, for a vehicle (100) for controlling a brake actuator (8) in a braked, stationary vehicle (100), comprising a sensor unit (5) for monitoring a state variable (Z1, Z2, Z3) that characterizes a load state of the vehicle (100), a displacement sensor (4) for detecting a distortion in the vehicle (100) caused by a change in level, and a control unit (6) that is connected in a signal-conducting manner to the sensor unit (5) and the displacement sensor (4), which is configured to release the brake actuator (8) in response to the detection of a distortion and, in the event that the state variable (Z1, Z2, Z3) is to be assigned to the predefined value range, to control a first target braking, and / or not to assign the state variable (Z1, Z2, Z3) to the predefined value range. is to control a second target braking.

16. Braking system (1) according to claim 15, characterized in that a load state is a position state and a state variable (Z1) is an angle of inclination (α) of the vehicle (100) relative to the horizontal, and wherein the sensor unit (5) has an acceleration sensor (5.1) for monitoring the angle of inclination (α).

17. Brake system (1) according to one of claims 15 or 16, characterized in that a load condition is a loading condition and a state variable (Z2) is a pressure of a suspension (3), and wherein the sensor unit (5) has a pressure sensor (5.2) for monitoring the pressure.

18. Braking system (1) according to one of claims 15 to 17, characterized in that a load condition is a loading condition and a state variable (Z3) is a compression travel of a mechanical suspension (3), and wherein the sensor unit (5) has a travel sensor (5.3) for monitoring the compression travel.

19. Vehicle (100), in particular commercial vehicle, with an axle (15, 16, 17), and a braking system (1) according to one of claims 15 to 18 for controlling a brake actuator (8).

20. Vehicle (100) according to claim 19, characterized in that the vehicle (100) is a truck combination, in particular an air-sprung truck combination, with a tractor (11) with an axle (15, 16) suspended on longitudinal control arms or semi-trailing arms, and a trailer connectable to the tractor (11) with an axle (17) suspended on longitudinal control arms or semi-trailing arms.

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