Brake device and method for controlling the braking process of a vehicle / trailer combination

Abstract

The invention relates to a method for controlling the braking process of a brake system of a vehicle / trailer combination, the vehicle / trailer combination consisting of a towing vehicle and at least one trailer, wherein in addition to the actuation of the brake of the towing vehicle, a target pressure for the brake of the trailer is set on the basis of a braking request, the target pressure correlating to an associated vehicle deceleration. During a normal operation, a target pressure for the trailer is assigned to the braking request in a first step. The method is characterized in that in a second step, the activation of an anti-lock braking system of the towing vehicle is regarded as a trigger to switch from an open-loop control mode to a closed-loop control mode of the brake system; in a third step, the actual deceleration of the towing vehicle is determined in the closed-loop control mode; and in a fourth step, the target pressure for the trailer is reduced so as to correspond to the assigned target pressure of a virtual braking request while taking into consideration the actual deceleration of the towing vehicle.

Description

[0001] ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16

[0002] Braking device and method for braking a vehicle

[0003] The present invention relates to a braking device and a method for controlling the braking of a vehicle combination consisting of a towing vehicle and at least one trailer. In particular, the vehicle combination is an agricultural vehicle combination consisting of an agricultural machine as the towing vehicle and at least one agricultural trailer. The agricultural machine can, for example, be a tractor, whereas the agricultural trailer, instead of being a trailer per se, can also be a braked implement for tillage or harvesting. Agricultural trailers are, in particular, loading wagons, platform trailers, tipper trailers, hooklift trailers, or transfer wagons, which can be designed as turntable or center-axle trailers with typically one to three axles.The invention also encompasses towing vehicles for road traffic, in particular trucks with at least one trailer. Specifically, the present invention relates to a method for controlling the braking of a vehicle combination of the type mentioned above, wherein the towing vehicle has a brake slip detection system and an anti-lock braking system (ABS). These systems counteract the locking of the braked wheels by automatically reducing the brake pressure, thus maintaining the vehicle's steerability and directional stability even under heavy braking or slippery road conditions.

[0004] Various braking systems and methods for brake control are known from the prior art. For example, DE 10 2013 007 881 A1 discloses a method for braking a towing vehicle-trailer combination in which a brake slip control is provided for the towing vehicle's braking system and either no brake slip control or a brake slip control is provided for the trailer's braking system. The trailer's braking system is controlled by the towing vehicle's braking system, and during braking, it is determined whether the trailer is at risk of, is about to, or has already begun to oscillate relative to the towing vehicle. The trailer's braking force or the trailer's braking performance is reduced if it is determined that the trailer is at risk of, is about to, or has already begun to oscillate. Furthermore, a braking device of a towing vehicle—ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16

[0005] A trailer combination is described in which the towing vehicle's braking system is equipped with a brake slip control system, and the trailer's braking system either lacks brake slip control or is equipped with brake slip control, with the trailer's braking system being controlled by the towing vehicle's braking system. The braking device includes a control and evaluation unit for determining, during braking, whether the trailer is at risk of, is about to, or has already begun to oscillate relative to the towing vehicle. The control and evaluation unit is designed to reduce the trailer's braking force or deceleration if, during braking, it is determined that the trailer is at risk of, is about to, or has already begun to oscillate.

[0006] Based on the known state of the art, the technical problem to be solved is to provide an improved method for controlling the braking of a vehicle combination. This problem is solved by the method according to the invention. The vehicle combination consists of a towing vehicle and one or more trailers. Depending on a braking request, a target pressure for the trailer's brake is set in addition to the application of the towing vehicle's brake. The towing vehicle's brake can be hydraulic, pneumatic, or electromechanical. The brake of at least one trailer is pneumatic or hydraulic. The braking request corresponds, for example, to a pedal travel of a brake pedal or a brake pressure specified via the brake pedal and is thus primarily specified by an operator of the towing vehicle.The braking request can also be triggered by a sensor system, in particular by a sensor system of an assistance system or a corresponding control unit. This would include systems for detecting obstacles, the road path and / or speed limits, and therefore sensor systems with radar, lidar and / or other imaging sensors (mono / stereo camera, thermal imaging camera).

[0007] The target pressure for the trailer brakes correlates with a corresponding vehicle deceleration. In other words, the system is designed so that an expected vehicle deceleration can be derived from a braking request, with the target pressure corresponding to this deceleration or being adjusted or set accordingly. ZF Friedrichshafen AG (file number 216478, Friedrichshafen, 2024-12-16) may use a parameter matrix or characteristic map for this purpose, which depicts a multitude of target pressure values ​​and vehicle decelerations. The parameter matrix or characteristic map may also include tolerance bands, which define the range of permissible target pressure values ​​for multiple vehicle deceleration values, or conversely, multiple permissible target pressure values ​​for a single vehicle deceleration value.Alternatively or additionally, an algorithm can be provided which determines a target pressure for the trailer's brake based on the braking requirement.

[0008] According to the invention, in normal operation, a vehicle deceleration and, based on this, a target pressure of the trailer are assigned in a first step to the braking request. Normal operation describes an operation of the braking system in which the braking request can be implemented without locking or impermissible slip of the braked wheels of the towing vehicle, and thus the vehicle deceleration is implemented according to the braking request. In a second step, activation of an anti-lock braking system of the towing vehicle is detected. This means that the implementation of the braking request leads to the braked wheels of the towing vehicle locking or at least exhibiting an impermissible slip value, so that the anti-lock braking system of the towing vehicle intervenes.For example, a slippery road surface or an excessively high braking demand, resulting in over-applying the brakes, can be the cause. Consequently, the actual deceleration of the towing vehicle may be lower than the corresponding vehicle deceleration. This intervention or activation of the anti-lock braking system (ABS) is considered a trigger in the inventive method to switch from control mode to regulation mode of the braking system. This means that, instead of simply applying a target pressure based on the braking demand, the actual deceleration of the towing vehicle is now determined in a third step. The actual deceleration can be determined using wheel speed sensors via the gradient of the vehicle speed, a GPS sensor, ground-based radar, or an accelerometer.

[0009] Based on the determined actual deceleration of the towing vehicle, and insofar as this deviates from the vehicle deceleration corresponding to the braking request (ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16), the target pressure of the trailer is reduced. Instead of the assigned vehicle deceleration based on the braking request, the actual deceleration is now assigned to a virtual braking request. The actual deceleration or the virtual braking request results in an adjusted target pressure for the trailer. In this case, this is lower than the original target pressure. The reduced target pressure causes the trailer brakes to generate less braking power. This is intended to prevent overbraking of the trailer. Thus, locking of the braked trailer wheels or oscillation can be effectively avoided.

[0010] In a further development of the method according to the invention, a fifth step involves taking the deactivation of the anti-lock braking system of the towing vehicle as a trigger to switch from the control operation back to the control operation of the braking system. Accordingly, the target pressure is again set depending on the original braking requirement. Subsequently, this pressure is then increased again to achieve a higher braking effect.

[0011] In addition, trigger debouncing can be implemented. This means that the next process step is not executed immediately upon trigger occurrence, but rather the condition or trigger must be present for a defined time interval before the next process step is implemented. This applies to both the activation and deactivation triggers of the anti-lock braking system. The same or different debouncing time intervals can be used for activation and deactivation. For example, the debouncing time can also vary depending on trailer-specific parameters.

[0012] In a further development of the procedure, a limit value is provided for the maximum reduction of the target pressure. This means that a minimum target pressure is defined, which must not be undercut by the reduction. This is intended to prevent situations where, in the case of particularly low actual deceleration, the trailer brakes are supplied with an excessively low or no target pressure, resulting in insufficient braking performance. For example, the limit value could represent a percentage of the original target pressure (ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16). In another version, the limit value could also be derived from the ranges of permissible assignments, meaning that the reduction process ensures that no impermissible assignment occurs. In other words, the limit value is then defined by the tolerance bands of the permissible assignments.

[0013] In a supplementary or alternative configuration, trailer-specific parameters are taken into account when reducing the target pressure. These include the number of braked axles on the trailer, its weight, and / or its load status (partially / unloaded / fully loaded). Depending on these parameters, the trailer can achieve a higher or lower braking effect without the braked wheels locking up. Accordingly, the system can be designed so that the lowering is less pronounced for a heavy or loaded trailer than for a light or unloaded trailer. The trailer-specific parameters can be provided via an automated data interface during coupling, or manually entered by the operator via a human-machine interface. Alternatively, they can be provided by a corresponding measuring device on the trailer.Particularly in vehicle combinations with significant weight differences between the towing vehicle and the at least one trailer, the inventive method or braking device can make a positive contribution to vehicle stabilization during braking. This applies especially to vehicle combinations where the towing vehicle weighs less than the trailer, in other words, vehicle combinations with a light towing vehicle and a heavy trailer.

[0014] According to a further aspect of the present invention, a control device for controlling a braking system is also included. The control device is designed and configured to execute the method according to the invention. For this purpose, the control device receives signals representing the braking request, the deactivation / activation of an anti-lock braking system, the actual deceleration of the towing vehicle, and / or trailer-specific parameters. These signals are processed as described above, and as a result, the virtual braking request and the reduced target pressure are determined. Finally, a signal to actuate the brakes of the towing vehicle and a signal to provide the target pressure for the trailer brakes are output.

[0015] Furthermore, the present invention comprises a vehicle combination consisting of a towing vehicle with a control device according to the invention and at least one trailer. The towing vehicle and the at least one trailer each have a brake which is controlled by the control device.

[0016] The present invention is further explained with reference to the single figure 1. This figure shows a diagram. The x-axis represents the target pressure p and the y-axis the vehicle deceleration a. A characteristic curve k is defined by dashed lines, which shows a correlation between permissible values ​​of the target pressure p for a given vehicle deceleration a and, conversely, permissible values ​​of the vehicle deceleration for a given target pressure. The characteristic curve k is limited by a maximum target pressure pmax and a maximum deceleration amax.

[0017] In this context, the target pressure p1 and the vehicle deceleration a1 represent a braking process during normal operation. The braking demand correlates with the vehicle deceleration a1, to which the target pressure p1 is assigned. When the trigger for activating the anti-lock braking system (ABS) is detected, the actual deceleration a2 is determined using the method according to the invention. This actual deceleration a2 is lower than the vehicle deceleration a1. Maintaining the target pressure p1 would result in an invalid assignment of the target pressure p1 for a given vehicle deceleration a2, as the intersection point s lies outside the characteristic curve k defined by dashed lines. Consequently, an adjustment of the target pressure p1 is necessary. This adjustment can be calculated using algorithms or derived from a parameter matrix or the characteristic curve k. Thus, the target pressure p1 is reduced by the value Ap, resulting in the target pressure p2.In this case, the target pressure p2 is reduced compared to the target pressure p1 such that it assumes the highest possible value within the characteristic curve k for the actual deceleration a2. However, alternative configurations are also conceivable in which the target pressure p2 assumes any other value permissible for the actual deceleration a2 within the characteristic curve k. For example, it could be stipulated that, in the case of ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16, the lowest permissible target pressure p2 is set during the reduction, while in normal operation the highest permissible target pressure p1 is set. Additionally or alternatively, the trailer-specific parameters can also be taken into account to determine whether the lowest or highest permissible target pressure p2 is set for the respective actual deceleration a2.For example, the highest permissible target pressure p2 can be set for a heavy and / or partially loaded trailer, while the lowest permissible target pressure p2 is set for a light and / or unloaded trailer. Furthermore, a combination of the aforementioned configurations is also conceivable.

[0018] ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16

[0019] Reference symbols a, a1, a2, amax; Delay p, p1, p2, pmax; Target pressure k; Characteristic curve

[0020] Ap reduction target pressure s intersection

Claims

ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16 Patent claims 1. Method for brake control of a braking system of a vehicle combination, the vehicle combination consisting of a towing vehicle and at least one trailer, wherein, depending on a braking request, in addition to the actuation of the brake of the towing vehicle, a target pressure (p, p1, p2, pmax) for the brake of the trailer is set, wherein the target pressure (p, p1, p2, pmax) correlates to an associated vehicle deceleration (a, a1, a2, amax), wherein in normal operation, in a first step, a target pressure (p1) of the trailer is assigned to the braking request, characterized in that in a second step, the activation of an anti-lock system of the towing vehicle is taken into account as a trigger to switch from a control operation to a regular operation of the braking system, wherein in a third step, an actual deceleration (a2) of the towing vehicle is determined in regular operation, wherein in a fourth step, the target pressure (p1) of the trailer is reduced such thatthat this corresponds to the assigned target pressure (p2) of a virtual brake request, taking into account the actual deceleration (a2) of the towing vehicle.

2. Method according to claim 1, wherein in a fifth step the deactivation of the anti-lock braking system of the towing vehicle is taken into account as a trigger in order to switch from the normal operation back to the control operation of the braking system.

3. Method according to claim 2, wherein a temporal debouncing of the trigger is provided.

4. Method according to one of the preceding claims, wherein a limit value for the maximum reduction of the target pressure (p, p1 , p2, pmax) is provided.

5. Method according to one of the preceding claims, wherein trailer-specific parameters are taken into account when reducing the target pressure (p, p1 , p2, pmax).

6. Control device for controlling a braking system, wherein the control device is designed and configured to perform the method according to one of the preceding claims, wherein the control device receives signals which constitute a braking request, a deactivation / activation of an anti-lock braking system, an actual- ZF Friedrichshafen AG File 216478 Friedrichshafen 2024-12-16 Deceleration (a2) of the towing vehicle and / or trailer-specific parameters are represented, these signals are processed and a virtual brake request and a target pressure (p, p1 , p2, pmax) are determined and a signal to actuate the brake of the towing vehicle and a signal to provide the target pressure (p, p1 , p2, pmax) for the brake of the trailer is output.

7. Vehicle combination consisting of a towing vehicle with a control device according to claim 6 and at least one trailer, wherein the towing vehicle and the at least one trailer each have a brake which is controlled by the control device.

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