Method and trailer braking system for correcting the clutch force control (CFC correction) in commercial vehicles with conventional commercial vehicle trailers

Abstract

The invention relates to a method for adjusting the braking effect of a conventional, non-powered trailer (2) of a vehicle combination with a front towing vehicle (1) during braking requested by the towing vehicle (1). According to the invention, the following steps are provided: a) Receiving a braking request (u) from the towing vehicle (1) via a communication interface (3); b) Measuring a longitudinal coupling force (F) acting in the longitudinal direction (L) of the vehicle by means of a sensor-equipped kingpin (7) on the trailer (2); c) Determining a deviation between the measured longitudinal coupling force (F) and a reference coupling force; d) Calculating a correction parameter limited in magnitude and / or slope as a function of at least the determined deviation and at least one state parameter of the trailer (2); e) Modulating a target braking parameter (u') within the trailer based on the braking request (u) using the calculated correction parameter.f) Controlling an EBS actuator (5) of the trailer (2) with the modified target braking value (u'); g) Deactivating or suppressing the modulation by a gating unit (6) when an ABS / ASR condition (12) is present, when at least one speed threshold is undershot (13) and / or when negative sensor diagnostic data (14) are present.;

Description

The invention relates to a method for adjusting the braking effect of a conventional trailer according to the preamble of claim 1, a trailer braking system according to claim 13, a computer program product according to claim 14 and a retrofit kit according to claim 15. The present invention relates generally to the control of electronically controlled braking systems of conventional semi-trailers / semi-trailers in road vehicle combinations. In particular, a coupling force-based correction of the trailer's internal braking effect is described, in which the longitudinal coupling force acting in the vehicle's longitudinal direction at the kingpin is continuously evaluated and used to modulate a target braking value for the trailer. In existing systems, trailer braking is predominantly based on target braking values ​​transmitted via bus systems (e.g., ISO 11992). However, tolerances (pad condition, temperature, pressure losses, nonlinearities) unfortunately lead to deviations between the requested braking effect and the actual trailer braking force generated. Robust, direct feedback of the measured longitudinal coupling force, including signal processing, plausibility checks, and safety-oriented gating (ABS / ASR priority, speed / diagnostic criteria), is currently neither possible nor established in operation with conventional trailers. This results in deficiencies in accuracy and robustness, as well as unnecessary longitudinal force fluctuations within the vehicle combination. DE 10 2023 117 135 A1 relates, for example, to a method for the autonomous control of a braking system of a trailer vehicle of a semi-trailer truck, in which a force acting on a kingpin of the trailer vehicle is determined, depending on which a brake signal for setting a braking force in the trailer vehicle is determined. DE 42 20 991 A1 describes a method and a device for electrical coupling force control in multi-part vehicles, in particular in fifth wheel couplings of a semi-trailer truck, in which high thrust forces occur during the braking process. DE 102 61 547 A1 further relates to a method for controlling the tensioning energy of a vehicle combination comprising a towing vehicle with at least one front axle and rear axle and a trailer vehicle with at least one trailer axle, wherein at least the towing vehicle has an electronically controlled braking system (EBS) that performs vehicle deceleration control (Z-control) and coupling force control (KKR). DE 42 43 245 A1 relates to a method for braking a vehicle train consisting of at least two individual vehicles. The object of the present invention is therefore to overcome the aforementioned disadvantages and to provide a method or trailer braking system that can transfer the deceleration requested by the towing vehicle to the conventional trailer with low tolerance, robustness, and without vibration excitation. In particular, ABS / ASR priority, compliance with compatibility bands, and reliable diagnostic / fallback strategies should be maintained. The main features of the invention are specified in the characterizing part of claim 1 and in claims 13, 14 and 15. Embodiments are the subject of claims 2 to 12. According to the invention, a method for adjusting the braking effect of a conventional, non-powered trailer of a vehicle combination with a front towing vehicle during braking requested by the towing vehicle comprises the following steps: a) Receiving a braking request from the towing vehicle via a communication interface; b) Measuring a longitudinal coupling force acting in the longitudinal direction of the vehicle by means of a sensor-equipped kingpin on the trailer; c) Determining a deviation between the measured longitudinal coupling force and a reference coupling force; d) Calculating a correction parameter limited in magnitude and / or slope as a function of at least the determined deviation and at least one state parameter of the trailer; e) Modulating an internal trailer braking setpoint based on the braking request using the calculated correction parameter; f) Controlling an EBS actuator of the trailer with the modified braking setpoint;g) Deactivating or suppressing modulation by a gating unit when an ABS / ASR condition is present, when at least one speed threshold is undershot and / or when negative sensor diagnostic data is present. In the context of the present invention, a "conventional trailer" is understood to be a towed cargo trailer or commercial vehicle trailer without its own electric or hybrid drive. It is exclusively "passively" connected to the towing vehicle and receives its braking commands via the standardized interface to the towing vehicle. Its braking effect is therefore entirely determined by external signals and is not supplemented by its own drive or recuperation systems. The trailer is typically mounted to the fifth wheel coupling of the towing vehicle via a kingpin. The "brake request" is the target braking torque or target braking pressure signal generated by the towing vehicle, which is transmitted to the trailer via a standardized data interface, in particular according to ISO 11992. It represents the desired deceleration by the driver or the vehicle system and forms the basis for the brake control in the trailer. The "communication interface" is the electrical and logical connection between the towing vehicle and trailer, through which braking requests, control data, and diagnostics are exchanged. It implements transmission according to standardized communication protocols and ensures the connection for all trailer-related control commands and feedback. The "sensor-equipped kingpin" is the central connecting element between the towing vehicle and the semi-trailer, which is additionally preferably equipped with at least one integrated sensor for measuring forces. In the invention, it serves to detect the longitudinal coupling force acting in the longitudinal direction of the vehicle, which directly provides information about the actual braking force transmission between the towing vehicle and the trailer. The "longitudinal coupling force" is the force acting in the direction of travel on the kingpin between the towing vehicle and the trailer due to driving dynamic loads. It results from the forces transmitted during braking and thus represents the real physical quantity used to determine deviations between the desired and actually achieved trailer braking performance. The "reference coupling force" is a target value derived from the deceleration requested by the towing vehicle and other vehicle dynamics parameters such as vehicle mass, speed, and gradient. It serves as the comparative value for the measured longitudinal coupling force and thus as the basis for determining deviations in brake force transmission. The deviation (abbreviated with the symbol e) is determined by subtracting the reference coupling force component from the longitudinal coupling force component. The "correction value" is a calculated control variable determined from the deviation between the measured longitudinal coupling force and the reference coupling force. Its magnitude and slope are limited to ensure system stability and compliance with compatibility bands, and it modulates the internal target braking value of the trailer. The "trailer-internal target brake value" is a target signal for brake application generated by the trailer's control unit. It is based on the brake request received from the towing vehicle, but is adjusted by the correction value so that the actual braking effect of the trailer corresponds as closely as possible to the deceleration desired by the towing vehicle. The "EBS actuators" typically comprise the valves, actuators, and pressure modulators of the trailer's electronic braking system, which translate the modified target braking force into a specific braking force applied to the trailer's wheels. They are the implementing element of the control system. The "gating unit" is a logical safety module that monitors the modulation of the target braking force and suppresses or deactivates it if necessary. It intervenes when ABS or ASR conditions are present, when the speed falls below a certain threshold, or when sensor diagnostics indicate faulty data. This ensures that modulation remains active only during safe and effective operating conditions. The inventive method or trailer braking system offers a number of advantages that contribute to solving the aforementioned problem. By measuring the actual longitudinal coupling force acting on the sensor-equipped kingpin in the vehicle's longitudinal direction, the resulting load transfer between the towing vehicle and trailer is directly recorded. This advantageously enables direct feedback of the actual forces into the trailer's braking control system. Deviations due to tolerances, aging, or non-linear components in the trailer braking system are effectively compensated for, resulting in a more precise implementation of the towing vehicle's braking request. Calculating a correction factor limited in magnitude and / or slope advantageously ensures that the modulation of the target braking force is not undamped, but rather controlled and smoothly adjusted. This prevents unwanted oscillations or unstable control responses in the vehicle combination, increasing driving stability and improving comfort for both driver and cargo.Longitudinal force fluctuations are effectively reduced. By incorporating state variables such as speed v, ABS / ASR states, or diagnostic parameters into the calculation of the correction value, the control system remains robust against changing road conditions, brake pad conditions, pressure fluctuations, or other external influences. This ensures that the braking effect is reliably maintained even under difficult conditions. The gating unit provided according to the invention advantageously ensures that the modulation of the target braking value is automatically deactivated or suppressed in the event of ABS or ASR intervention, at low speeds, or in the case of detected sensor defects. This prevents incorrect control, protects against overbraking, and ensures that safety systems are prioritized and take precedence at all times.Since the method precisely regulates the longitudinal coupling force to a low-tolerance level, the peak mechanical loads on the coupling, frame, and brake components are reduced. This directly contributes to less material fatigue and a longer service life for the vehicle components. The driver of the towing vehicle benefits from a smooth deceleration response across the entire vehicle combination. The risk of the trailer "pushing" or "pulling" is effectively minimized, resulting in improved directional stability, smoother handling, and increased subjective driving safety. According to the invention, the core logic of a coupling force-based brake correction is already defined. This can easily be extended later—for example, for fleet optimization, predictive control and operating strategies, or an enhanced coupling force control (CFC) system interacting with the towing vehicle.The invention thus does pioneering work and advantageously provides a basic technology for future-proof trailer braking systems. According to a further aspect of the invention, a trailer braking system can be provided for carrying out the method, comprising a communication interface, a sensor-equipped kingpin, a signal processing unit, a correction unit, a gating unit, an EBS actuator and a central electronic control unit, wherein the control unit can be configured to perform the steps of the method. The specific system architecture, comprising a communication interface, kingpin sensor, signal processing, correction and gating unit, and EBS actuator, provides a fully integrated trailer braking system. This enables a compact and standardized implementation, reduces implementation effort, and simplifies retrofitting. Furthermore, all relevant functional blocks can work together in a harmonized unit, thereby improving robustness and operational reliability. Preferably, the reference coupling force can be adaptively determined from a target deceleration, an estimated total vehicle mass and / or a road or track gradient, with the option of additional temperature- or speed-dependent parameterization. The adaptive determination of the reference coupling force advantageously allows for dynamic adjustment to current vehicle and environmental conditions such as mass, gradient, temperature, and speed. This ensures precise brake control even when the load or road conditions change. This significantly improves the accuracy and reliability of deceleration implementation. Preferably, the signal processing unit can be configured to filter the sensor signal of the measured longitudinal coupling force and to perform a dynamic offset or zero-point adjustment. The signal processing unit with filtering and dynamic offset adjustment advantageously ensures that the measured coupling force can be robustly and reliably incorporated into the control system. This results in reliable force measurement without systematic errors or drift, which stabilizes the control performance and reduces maintenance requirements. According to a preferred embodiment, the correction factor can be calculated from the determined deviation using PL and / or PID control with anti-windup measures. By using a PI or PID controller with combined anti-windup, corrections are implemented quickly, stably, and without overdriving. This advantageously results in very high control accuracy with rapid adaptation to deviations and simultaneous avoidance of instabilities. Consequently, the overall driving stability of the entire train or semi-trailer combination is improved. According to another design variant, the correction value can be limited by map-based and / or rule-based saturations, so that compatibility bands of the trailer braking system are maintained. Limiting the correction value within predefined compatibility bands prevents the trailer from being oversteered and simultaneously ensures interchangeability with different tractor units. This advantageously enables cross-manufacturer and cross-fleet interoperability as well as increased operational reliability. Preferably, the gating unit can additionally perform a plausibility check of the longitudinal coupling force against pressure or torque estimates derivable from the EBS actuator, whereby the modulation can be deactivated if a plausibility violation is detected. The plausibility check of the coupling force against pressure or torque estimates from the EBS actuator advantageously enables the automatic detection of faulty sensor data. This results in a high level of functional reliability, as erroneous measurements are immediately detected and compensated for, effectively preventing unintended interventions. According to another preferred embodiment, the activation of the modulation can take place above a speed threshold, for example at about 10 km / h, while the deactivation below this speed threshold can be achieved by hysteresis based on the vehicle speed. Activating and deactivating the modulation based on a speed threshold, e.g., at 10 km / h, prevents incorrect control during standstill or shunting operations. This results in robust and practical functionality that is only activated when actually needed. Preferably, if a predetermined warning threshold for the correction parameter is exceeded, a driver or workshop message can be issued, and a diagnostic data set can also be stored in the sensor diagnostic data. Issuing warning messages when a correction threshold is exceeded, as well as storing this information in diagnostic data, creates transparency and advantageously supports predictive maintenance. The main benefit is increased availability of the vehicle combination through early detection and reporting of wear or malfunctions. Preferably, the sensor-equipped kingpin can comprise at least one strain gauge, magnetoelastic, piezoelectric, fiber optic or SAW sensor, wherein the sensor-equipped kingpin can be designed as an interchangeable retrofit component for existing conventional trailers. The sensor-equipped kingpin, as a replaceable component, allows for the easy retrofitting of existing trailer fleets. The advantage is a cost-effective modernization without interfering with the existing brake architecture, making the invention suitable for large-scale application. The at least one sensor ensures that the longitudinal coupling force can be measured. According to a preferred embodiment, the communication interface can utilize a bus system for trailer braking functions, preferably according to ISO 11992, and additionally provide diagnostic and warning messages to the front towing vehicle. The use of a standardized bus system for trailer braking functions ensures compatibility with existing tractor units. This advantageously allows for easy integration into current commercial vehicle architectures while simultaneously providing reliable diagnostic and warning messages to the driver. According to a further design variant, the correction parameter can be used exclusively for internal adjustment of a trailer-internal braking characteristic curve, without changing the braking requirements transmitted by the towing vehicle. Using only the correction parameter for internal adjustment of the brake characteristic curve prevents any changes to the brake signal requested by the towing vehicle. This creates a clear system separation: the towing vehicle remains unchanged, while the trailer is internally optimized. This advantageously increases legal certainty and minimizes interventions in existing vehicle architectures. According to a preferred embodiment, the central electronic control unit can calculate a control variable for coupling force control from the longitudinal coupling force and the reference coupling force, which can be provided to the front towing vehicle for control via the communication interface. Providing a control variable for coupling force regulation in the towing vehicle expands the system's functionality. The resulting key advantage is comprehensive vehicle combination control, which allows for an even more harmonious distribution of braking force between the towing vehicle and trailer. According to another aspect of the invention, a computer program product can be provided which is executable on the central electronic control unit and, when executed, performs the method, additionally enabling an over-the-air update of parameters of the signal processing unit and the correction unit. The software-based computer program advantageously allows for implementation on the control unit and easy updates via over-the-air mechanisms. This offers the advantage of high future-proofing and adaptability without requiring physical modifications to the hardware. According to another aspect of the invention, a retrofit kit can be provided which, when installed in an existing trailer, provides the trailer braking system, wherein the kit can include the sensor-equipped kingpin, the central electronic control unit, a signal processing unit, a correction unit, and connection means for the communication interface and the EBS actuator. The retrofit kit enables the simple equipping of existing standard trailers with the braking system according to the invention for carrying out the method according to the invention. This advantageously achieves a broad market launch without the need to develop complete new trailer braking systems, thus allowing existing fleets to be modernized quickly. Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. Figure 1 shows a schematic representation of the trailer braking system according to the invention, adapted to a towing vehicle-trailer combination for carrying out the method according to the invention. Fig. 1 schematically shows a method or braking system for adjusting the braking effect of a conventional, non-powered trailer 2 of a vehicle combination with a front towing vehicle 1, during a braking action requested by the towing vehicle 1. It is provided that a braking request u is received from the towing vehicle 1 via a communication interface 3. Furthermore, it is shown schematically that a longitudinal coupling force F acting in the longitudinal direction L of the vehicle is measured on the trailer 2 by means of a sensor-equipped kingpin 7. From the measured longitudinal coupling force F, a deviation from a reference coupling force is then determined. Depending on at least the determined deviation and at least one state variable of the trailer 2, a correction value limited in magnitude and / or slope is calculated. Based on the braking demand u and using the calculated correction value, a target braking value u' is modulated for the trailer. The trailer's EBS actuator 5 is controlled with the modified target braking value u'. A gating unit 6 deactivates or suppresses the modulation if an ABS / ASR condition 12 is present, if at least one speed threshold 13 is undershot, and / or if negative sensor diagnostic data 14 is present. In a further aspect, the invention relates to the schematically depicted trailer braking system, generally designated by 10. The trailer braking system 10 is configured to carry out the method according to the invention. This can comprise a communication interface 3, a sensor-equipped kingpin 7, a signal processing unit 8, a correction unit 9, a gating unit 6, an EBS actuator 5, and a central electronic control unit 11, which can be configured to execute the method steps a) to g). The reference coupling force can be adaptively determined from a target deceleration, an estimated total vehicle mass and / or a road or track gradient, with the option of additional temperature- and speed-dependent parameterization. The signal processing unit 8 can filter the sensor signal of the measured longitudinal coupling force F and perform a dynamic offset or zero point adjustment. Furthermore, the correction factor can be calculated from the determined deviation using PI and / or PID control with anti-windup measures. Furthermore, the correction value can be limited by map-based and / or rule-based saturations so that compatibility bands of the trailer braking system 10 are maintained. The gating unit 6 can additionally perform a plausibility check of the longitudinal coupling force F against pressure or moment estimates derivable from the EBS actuator 5, whereby the modulation can be deactivated if a plausibility violation is detected. Furthermore, the activation of the modulation can occur above a speed threshold 13, for example at 10 km / h, while the deactivation below this speed threshold can be achieved through hysteresis based on the vehicle speed v. If a predefined warning threshold is exceeded, a driver or workshop message can be issued for the correction parameter and a diagnostic data set can be stored in sensor diagnostic data 14. The sensor-equipped kingpin 7 can include at least one strain gauge, magnetoelastic, piezoelectric, fiber optic or SAW sensor and can be designed as an interchangeable retrofit component for existing conventional trailers 2. Furthermore, the communication interface 3 can utilize a bus system for trailer braking functions, in particular according to ISO 11992, whereby diagnostic and warning messages can be provided to the front towing vehicle 1. The correction parameter can only be used for internal adjustment of a trailer's internal braking characteristic curve, without changing the braking requirements u transmitted by the towing vehicle 1. Furthermore, the central electronic control unit 11 can calculate a control variable for coupling force control from the longitudinal coupling force F and the reference coupling force, which can be provided to the front towing vehicle 1 for control via the communication interface 3. Furthermore, a computer program product may be provided that is executable on the central electronic control unit 11 and, when executed, effects the procedure, additionally enabling an over-the-air update of parameters of the signal processing unit 8 and the correction unit 9. Finally, a retrofit kit can be provided which, when installed in an existing trailer 2, provides the trailer braking system 10 and includes the sensor-equipped kingpin 7, the central electronic control unit 11, a signal processing unit 8, a correction unit 9 and connection means for the communication interface 3 and the EBS actuator 5. Reference symbol list L Longitudinal direction of travel and vehicle Q Lateral direction of vehicle (perpendicular to the longitudinal direction of travel and vehicle) u Brake request (via ISO 11992 interface) u' Trailer-internal target brake force (modified) F Longitudinal coupling force (at the sensor-equipped kingpin) 1 Front towing vehicle (tractor unit of a commercial vehicle) 2 Towed trailer (conventionally towed, without its own drive) 3 Communication interface 5 EBS actuator (actuator of the trailer's electronic braking system) 6 Gating unit 7 Sensor-equipped kingpin (with at least one sensor) 8 Signal conditioning unit (with filter and offset estimator) 9 Correction unit 10 Trailer braking system (for vehicle combination of towing vehicle / trailer) 11 Central electronic control unit (trailer ECU, CFC correction logic) 12 ABS / ASR states 13 Speed ​​threshold 14 Sensor diagnostic data

Claims

Method for adjusting the braking effect of a conventional, non-powered trailer (2) of a vehicle combination with a front towing vehicle (1) during braking requested by the towing vehicle (1), characterized by the following steps: a) Receiving a braking request (u) from the towing vehicle (1) via a communication interface (3); b) Measuring a longitudinal coupling force (F) acting in the longitudinal direction (L) of the vehicle by means of a sensor-equipped kingpin (7) on the trailer (2); c) Determining a deviation between the measured longitudinal coupling force (F) and a reference coupling force; d) Calculating a correction quantity limited in magnitude and / or slope as a function of at least the determined deviation and at least one state variable of the trailer (2); e) Modulating a trailer-internal braking setpoint (u') based on the braking request (u) using the calculated correction quantity;f) Controlling an EBS actuator (5) of the trailer (2) with the modified target braking value (u'); g) Deactivating or suppressing the modulation by a gating unit (6) when an ABS / ASR condition (12) is present, when at least one speed threshold (13) is undershot and / or when negative sensor diagnostic data (14) is present.; Method according to claim 1, characterized in that the reference coupling force is adaptively determined from a target deceleration, an estimated total vehicle mass and / or a road / track gradient and / or is parameterized depending on temperature and speed. Method according to one of the preceding claims, characterized in that a signal conditioning unit (8) is configured to filter the sensor signal of the measured longitudinal coupling force (F) and to perform a dynamic offset / zero point adjustment. Method according to one of the preceding claims, characterized in that the correction quantity is calculated from the deviation formed by means of PI and / or PID control with anti-windup measures. Method according to one of the preceding claims, characterized in that the correction quantity is limited by map-based and / or rule-based saturations, such that compatibility bands of the trailer braking system (10) are maintained. Method according to one of the preceding claims, characterized in that the gating unit (6) additionally performs a plausibility check of the longitudinal coupling force (F) against pressure / torque estimates derivable from the EBS actuator (5), wherein the gating unit (6) deactivates the modulation upon detection of a plausibility violation. Method according to one of the preceding claims, characterized in that the activation of the modulation above the speed threshold (13), preferably of 10 km / h, and the deactivation below the speed threshold (13), preferably by means of hysteresis based on a vehicle speed, takes place. Method according to one of the preceding claims, characterized in that, when a predetermined warning threshold for the correction parameter is exceeded, a driver / workshop message is issued and a diagnostic data set is stored in sensor diagnostic data (14). Method according to one of the preceding claims, characterized in that the sensor-equipped kingpin (7) comprises at least one strain gauge, magnetoelastic, piezoelectric, fiber optic or SAW sensor, wherein the sensor-equipped kingpin (7) is designed as an interchangeable retrofit component for existing conventional trailers (2). Method according to one of the preceding claims, characterized in that the communication interface (3) uses a bus system for trailer braking functions and provides diagnostic / warning messages to the front towing vehicle (1). Method according to one of the preceding claims, characterized in that the correction parameter is used exclusively for the internal adjustment of a trailer-internal braking characteristic curve, without changing the braking requirements (u) of the towing vehicle (1). Method according to one of claims 1 to 10, characterized in that the central electronic control unit (11) calculates a control variable for coupling force control from the longitudinal coupling force (F) and the reference coupling force and provides this control variable to the front towing vehicle (1) for control via the communication interface (3). Trailer braking system (10), designed and equipped to carry out the method according to one of the preceding claims, comprising a communication interface (3), a sensor-equipped kingpin (7), a signal conditioning unit (8), a correction unit (9), a gating unit (6), an EBS actuator (5) and a central electronic control unit (11) configured to perform steps (a) to (g) of the method. Computer program product that is executable on the central electronic control unit (11) and, when executed, performs the method according to one of claims 1 to 12. Retrofit kit (kit-of-parts) for retrofitting a conventional trailer (2) with the trailer braking system (10) according to claim 13, wherein the retrofit kit, when installed in an existing trailer (2), provides the trailer braking system (10) according to claim 13, comprising the sensor-equipped kingpin (7), the central electronic control unit (11), a signal processing unit (8), a correction unit (9), and connection means for the communication interface (3) and the EBS actuator (5).

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