Braking method for a vehicle combination, and control device

Abstract

The present invention relates to a braking method for a vehicle combination (1) and to a control device (37) for carrying out said method, wherein the braking method comprises the following steps: - detecting a braking request (11), - outputting an initial brake pressure (pO) to a trailer braking system (9), - detecting a resulting actual longitudinal acceleration aLong and an actual transverse acceleration aLat of the vehicle combination (1), - determining a minimum friction coefficient MFC taking into account the detected actual longitudinal acceleration aLong and the actual transverse acceleration aLat, - determining a subsequent brake pressure (pn) for the trailer braking system (9) on the basis of the minimum friction coefficient MFC, - outputting the subsequent brake pressure (pn) to the trailer braking system (9) in accordance with the braking request (11).

Description

[0001] Braking procedure for a trailer and control unit

[0002] The present invention relates to a braking method for a vehicle combination and a control device which is designed to carry out the braking method according to the invention and to a vehicle combination with a control device according to the invention.

[0003] A combination consists of a towing vehicle and at least one trailer, with trucks and semi-trailers in particular falling under this term.

[0004] Critical driving situations can arise, particularly during braking, if, for example, the towing vehicle and trailer are braked to different degrees.

[0005] This can, for example, cause the trailer to swing out of control, the vehicle to skid, or jackknife, all of which represent uncontrollable and therefore dangerous driving conditions. The goal is always to avoid such critical driving situations.

[0006] In order to increase the driving safety of trailers, modern trailers can be equipped with a variety of sensors and assistance systems, such as articulation angle sensors, towing vehicle and trailer anti-lock braking systems (ABS), traction control (ASR) and an electronic towing vehicle and trailer stability program (ESP).

[0007] EP 3 727 965 B1 discloses a braking method for a trailer in which the stability of the trailer is monitored during braking operations, in particular the articulation angle between the towing vehicle and the trailer.

[0008] EP 1 427 619 B1 discloses a braking method for a trailer combination in which the driving condition of the trailer combination is monitored, in particular for the presence of unstable driving conditions, in order to reduce the braking torque of the trailer if an unstable driving condition is detected. DE 10 2021 121 833 A1 discloses a braking method for a trailer combination in which the brake force is distributed between the towing vehicle and the trailer depending on the detected driving condition information, preferably with a trailer ABS.

[0009] All of these publications use a multitude of systems and sensors, which in turn increases complexity, the likelihood of failure and, last but not least, costs.

[0010] In the event of a failure, for example, of the trailer ABS, one strategy may be to brake the trailer with significantly reduced braking force to prevent unstable driving situations. However, this reduces the overall braking force of the trailer combination, which in turn results in longer braking distances, which can lead to critical driving situations.

[0011] It is therefore the object of the present invention to provide a safe and effective braking method for a trailer combination, in particular in the event that no or no functioning trailer ABS is available.

[0012] This object is achieved according to the invention by a braking method for a combination, wherein the combination is formed by a towing vehicle with a towing vehicle braking system and at least one trailer with a trailer braking system, wherein the trailer braking system does not have a functioning trailer ABS and the braking method comprises the following steps:

[0013] - Detecting a braking request,

[0014] - Control of an initial brake pressure (pO) to the trailer brake system,

[0015] - Recording a resulting actual longitudinal acceleration (aLong) and an actual lateral acceleration (aLat) of the vehicle combination,

[0016] - Determination of a minimum friction coefficient (MFC) taking into account the recorded actual longitudinal acceleration (aLong) and the actual lateral acceleration (aLat),

[0017] - Determining a follow-up brake pressure (pn) for the trailer brake system depending on the minimum friction coefficient (MFC),

[0018] - Control of the follow-up brake pressure (pn) to the trailer brake system in accordance with the braking request. The braking request can be detected, for example, based on a driver input via a brake pedal in the towing vehicle. Braking requests from assistance systems, such as an emergency braking system (AEB) or cruise control (ACC), as well as braking requests from autonomous systems, can also be detected.

[0019] The towing vehicle braking system and the trailer braking system are preferably connected to each other in a pressure-conducting and / or signal-conducting manner so that a braking request detected in the towing vehicle can be forwarded to the trailer.

[0020] The coefficient of friction is a measure of the maximum possible power transmission between the wheels of the vehicle and the road.

[0021] Applying the initial brake pressure (pO) to the trailer braking system causes the trailer brakes to be applied and the braked trailer wheels to be decelerated. The initial brake pressure (pO) is preferably selected such that it is sufficiently high to induce, in particular, a (negative) actual longitudinal acceleration (aLong), but at the same time is low enough to prevent the braked trailer wheels from locking, even under road conditions with a low coefficient of friction, such as snow, ice, or rain.

[0022] The actual longitudinal acceleration (aLong) and the actual lateral acceleration (aLat) are preferably recorded using acceleration sensors or sensors whose data can be used to derive the actual longitudinal acceleration (aLong) and the actual lateral acceleration (aLat). The sensors are preferably part of the towing vehicle.

[0023] Whenever an increase in the actual longitudinal acceleration (aLong) or the actual lateral acceleration (aLat) is mentioned below, only the magnitude of the latter is considered. Increased braking of the vehicle / trailer combination therefore corresponds, in particular, to an increase in the (negative) actual longitudinal acceleration. The minimum friction coefficient (MFC) corresponds to the minimum friction coefficient that can be assumed between the wheel and the road.

[0024] The minimum coefficient of friction (MFC) is determined taking into account the recorded actual longitudinal acceleration aLong and the actual lateral acceleration aLat. For example, a minimum coefficient of friction (MFC) can be determined based on a negative actual longitudinal acceleration, i.e., deceleration.

[0025] At the beginning of the braking process, no information is available about the existing coefficient of friction between the trailer's wheels and the road. After braking has been completed using the initial brake pressure (pO), the minimum coefficient of friction (MFC) can be determined again. This minimum coefficient of friction (MFC) can then be assumed for the subsequent braking process with the follow-up brake pressure (pn). Based on the knowledge of the minimum coefficient of friction (MFC), the follow-up brake pressure pn can thus be increased preferentially without the braked trailer wheels locking and creating an unstable and / or critical driving situation.

[0026] The assignment of different follow-up brake pressures pn to different minimum friction coefficients (MFC) can, for example, be carried out according to a predefined assignment rule. The basic relationship is that the higher the minimum friction coefficient (MFC), the higher the follow-up brake pressure (pn) can be selected.

[0027] The control of the follow-up brake pressure (pn) occurs in accordance with the braking request, which means that braking is only carried out as hard as requested.

[0028] If the follow-up brake pressure pn possible due to the determination of the minimum friction coefficient (MFC) would lead to a greater deceleration than the brake request provides, braking is only carried out with the pressure required for the brake request.

[0029] If the possible follow-up brake pressure (pn) determined based on the minimum friction coefficient (MFC) is insufficient to meet the braking request, braking is still only carried out with the possible follow-up brake pressure (pn) to avoid an unstable and / or critical driving situation. The follow-up brake pressure pn thus specifies an upper limit for the pressure applied to the trailer braking system.

[0030] This avoids critical and dangerous driving situations caused by braking, such as swinging of the trailer, skidding of the vehicle or jackknifing, even with trailers that do not have or do not have a functioning trailer ABS.

[0031] At the same time, a high overall braking force of the trailer combination is achieved, since the follow-up brake pressure pn, which can be controlled to the trailer brake system, achieves a significantly higher braking effect than would be the case if the trailer were only braked across the board with a greatly reduced braking force.

[0032] Furthermore, this object is achieved according to the invention by a control unit for a braking system, wherein the control unit is configured to carry out the method according to the invention.

[0033] The control unit is preferably arranged in the towing vehicle, for example it can be a brake control unit of the towing vehicle, which is designed to carry out the method according to the invention.

[0034] Furthermore, this object is achieved according to the invention by a combination comprising a towing vehicle with a towing vehicle braking system and at least one trailer with a trailer braking system and a control device according to the invention for carrying out the method according to the invention.

[0035] The advantages described above arise analogously.

[0036] According to a first embodiment of the method, the minimum coefficient of friction (MFC) is determined according to the formula where aLat is the actual lateral acceleration, aLong is the actual longitudinal acceleration, and g is the acceleration due to gravity. Calculating the square sum of the actual lateral acceleration aLat and the actual longitudinal acceleration aLong, normalized by the acceleration due to gravity, has proven to be a good measure of the minimum coefficient of friction (MFC).

[0037] According to a further embodiment of the method, the method is carried out repeatedly, preferably continuously, wherein in each case the follow-up brake pressure (pn) is considered as the initial brake pressure (pO) of the subsequent follow-up brake pressure (pn+1).

[0038] This creates an iterative process. Typically, by controlling the initial brake pressure (pO), only a low braking force is generated by the trailer brake system, which in particular only results in a low (negative) actual longitudinal acceleration (aLong). The actual longitudinal acceleration (aLong) is an input variable for determining the minimum friction coefficient (MFC). The follow-up brake pressure pn, in turn, can be higher than the initial brake pressure (pO), since the minimum friction coefficient (MFC) is known. A higher follow-up brake pressure (pn), in turn, causes a higher braking force from the trailer brake system. The higher braking force causes a higher (negative) actual longitudinal acceleration (aLong), which means that the resulting minimum friction coefficient (MFC) is higher. The subsequent follow-up brake pressure (pn+1) can now in turn be higher than the follow-up brake pressure (pn), which in turn results in a further increase in the braking force.

[0039] This procedure is preferably repeated or performed continuously until the actual longitudinal acceleration aLong no longer increases. Thus, the minimum friction coefficient (MFC) also no longer increases, and the resulting follow-on brake pressure also remains constant.

[0040] Furthermore, changes in road conditions can be detected through a repeated, preferably continuous process, after which the applied follow-up brake pressure pn can be adjusted. For example, a slippery road section would lead to a drop in the (negative) actual longitudinal acceleration (aLong), which in turn would result in a lower minimum friction coefficient (MFC) and a correspondingly lower subsequent follow-up brake pressure (pn+1).

[0041] According to a further embodiment of the method, the method further comprises the step

[0042] - Recording load condition information of the trailer combination, wherein the load condition information is additionally taken into account when determining the follow-up brake pressure pn and / or when controlling the initial brake pressure (pO), preferably in such a way that the follow-up brake pressure pn and / or the initial brake pressure (pO) for the trailer brake system is increased with increasing load condition.

[0043] The coefficient of friction, and thus the maximum transferable force between the wheels of the trailer and the road, depends heavily on the weight, i.e., the load acting on the respective wheels. The follow-up brake pressure pn and / or the initial brake pressure (pO) can be higher in a loaded vehicle than in an unloaded vehicle.

[0044] Preferably, a predetermined follow-up brake pressure pn and / or initial brake pressure (pO) is provided for a specific minimum friction coefficient (MFC) and a specific vehicle load condition, in particular such that as the minimum friction coefficient (MFC) and the vehicle load condition increase, the follow-up brake pressure pn and / or initial brake pressure (pO) also increase. The relationship between the load condition and the follow-up brake pressure (pn) and / or initial brake pressure (pO) to be controlled can, for example, be linear.

[0045] The load condition information can be recorded in various known ways using load sensors, for example by means of suspension or bellows pressure monitoring, tire pressure monitoring or force sensors.

[0046] According to a further embodiment of the method, the method further comprises the step

[0047] - detecting curve radius information, wherein the curve radius information is additionally taken into account when determining the follow-up brake pressure (pn) and / or when controlling the initial brake pressure (pO), preferably in such a way that the follow-up brake pressure (pn) and / or the initial brake pressure (pO) for the trailer brake system is reduced with decreasing curve radius.

[0048] The reduction of the follow-up brake pressure (pn) and / or the initial brake pressure (pO) for the trailer brake system with decreasing curve radius is preferably understood to mean that the respective follow-up brake pressure (pn) and / or initial brake pressure (pO) is lower for a small curve radius than for a larger curve radius.

[0049] Depending on the curve radius information, a choice can be made regarding a braking strategy, in particular such that if the curve radius is below a limit value, for example 300 m curve radius or 200 m curve radius, a curve braking strategy is selected, while above the limit value a straight-ahead driving strategy is selected.

[0050] Within the cornering braking strategy, the focus can be on the stability of the vehicle / trailer combination, and in particular, a low initial brake pressure (pO) can be applied. In contrast, within the straight-ahead driving strategy, the focus can be on achieving high braking forces, and in particular, a higher initial brake pressure (pO) can be applied, resulting in a shorter braking distance for the vehicle / trailer combination.

[0051] The curve radius information can be acquired in various known ways, for example, using a steering angle sensor, an articulation angle sensor, wheel speed sensors, in particular a comparison of individual wheel speeds on each side, lateral acceleration sensors in combination with the speed of the vehicle / trailer combination, or camera systems. Furthermore, the curve radius information can be obtained using a yaw rate sensor in combination with the speed of the vehicle / trailer combination, by comparing the actual yaw rates with the target yaw rates, and / or by comparing the longitudinal and lateral acceleration.

[0052] According to a further development of the previous embodiment of the method, the maximum brake pressure for the towing vehicle brake system is limited as a function of the curve radius information, preferably in such a way that the maximum brake pressure for the towing vehicle brake system is reduced as the curve radius decreases.

[0053] The relationship between the reduction of the maximum brake pressure for the towing vehicle brake system and a decreasing curve radius applies analogously to the statements in the previous embodiment.

[0054] This prevents the trailer from pushing too hard onto the towing vehicle. Especially when cornering, pushing the trailer too hard onto the towing vehicle can lead to instability, such as jackknifing.

[0055] According to a further embodiment of the method, the initial brake pressure pO is controlled as a function of curve radius information, in particular as a function of a minimum friction coefficient (MFC) dependent on the actual lateral acceleration aLat, which preferably is determined according to calculated, where aLat is the actual lateral acceleration, aLong is the actual longitudinal acceleration and g is the acceleration due to gravity.

[0056] When cornering, which is assumed, for example, when the curve radius is below a certain limit, such as a 300m or 200m curve radius, an actual lateral acceleration (aLat) already occurs depending on the speed of the vehicle / trailer combination. This actual lateral acceleration (aLat), which only occurs due to cornering, i.e., especially without braking intervention, can be used to determine a minimum coefficient of friction (MFC).

[0057] Thus, the minimum friction coefficient (MFC) resulting from cornering can already be taken into account when adjusting the initial brake pressure (pO), and in particular, the initial brake pressure (pO) can be higher than if no information about the minimum friction coefficient (MFC) is available. This results in a shortened braking distance for the vehicle combination. According to a further embodiment of the method, the initial brake pressure (pO) is adjusted depending on

[0058] - the speed (v) of the vehicle combination and / or

[0059] - a temperature signal from an outside temperature sensor and / or

[0060] - a windscreen wiper signal from a windscreen wiper sensor / rain sensor and / or

[0061] - map / navigation information data and / or

[0062] - previous minimum friction coefficient (MFC) determinations are modulated.

[0063] The speed v of the trailer significantly influences the behavior and, in particular, the stability of the trailer during braking. At higher trailer speeds (v), it may therefore be necessary to apply lower initial brake pressures (pO) than at lower trailer speeds (v).

[0064] The outside temperature can be an indicator of the current road conditions. For example, at an outside temperature significantly above 0°C, black ice is not immediately expected, which means that the initial brake pressure (pO) applied may be higher than if there is a risk of black ice.

[0065] Even a windshield wiper sensor / rain sensor can provide limited information about road conditions, especially whether the road is wet or dry. On dry roads, the initial brake pressure (pO) applied may be higher than on wet roads.

[0066] The map / navigation information may include information about the type of road surface, such as gravel or asphalt. On an asphalt road, the initial brake pressure (pO) applied can typically be higher than on a gravel road.

[0067] Previous braking events / previous minimum friction coefficient (MFC) determinations can also be an indicator of road conditions to a certain extent. For example, if previous braking events already suggest a high minimum friction coefficient (MFC), the initial brake pressure (pO) applied during a subsequent braking event can ideally be higher. All or at least some of the sensor data and information described above are already available in a modern vehicle / trailer combination. Using this data and information makes it possible to better adapt the initial brake pressure (pO) to the actual road conditions, which in turn shortens the braking distance of the vehicle / trailer combination.

[0068] According to a further embodiment of the method, the determination of the follow-up brake pressure (pn) for the trailer brake system takes place as a function of the minimum friction coefficient (MFC) and / or curve radius information and / or load condition information of the trailer combination by means of a previously defined assignment rule, preferably at discrete intervals.

[0069] The assignment rule can, for example, be provided in the form of data stored in the towing vehicle in the form of electronically accessible tables or control curves. Using the previously defined assignment rule, the recorded and determined dependencies can be processed quickly and reliably.

[0070] The choice of discrete intervals can, for example, provide for the classification of the determined minimum coefficient of friction (MFC) into a predefined number of ranges or intervals. Similar intervals or ranges can also be provided for the curve radius information and / or charge state information. By providing discrete intervals, complexity can be reduced.

[0071] According to a further embodiment of the method, the initial brake pressure (pO) and / or the subsequent brake pressure (pn) is / are applied to the trailer brake system for a limited time, preferably in a pulsed manner.

[0072] In particular, pulsing the initial brake pressure (pO) can reduce negative effects caused by locking the braked trailer wheels, as these wheels only lock for a short time. This can be the case, for example, if the initial brake pressure (pO) applied was set too high for the actual road conditions. The provision of time-limited, preferably pulsed initial brake pressures (pO) and / or follow-up brake pressures thus has similar advantages and disadvantages to a stutter brake.

[0073] According to a further embodiment of the method, the method further comprises the step

[0074] - Detection of a coupling force between trailer and towing vehicle, whereby once a coupling force limit is exceeded, the maximum brake pressure for the towing vehicle brake system is limited, preferably in such a way that jackknifing is prevented.

[0075] By measuring the coupling force between the trailer and towing vehicle, excessive pushing of the trailer onto the towing vehicle can be detected. In response to exceeding the (negative) coupling force limit, the maximum brake pressure for the towing vehicle's braking system is limited so that the (negative) coupling force, or pushing, does not increase any further. This prevents jackknifing in particular and maintains driving stability.

[0076] The coupling force can be measured in a known manner, for example by means of a load cell in the coupling mouth of the towing vehicle.

[0077] According to a further embodiment of the method, the method further comprises the step

[0078] - detecting a yaw rate of the towing vehicle, preferably with a yaw rate sensor, wherein once a yaw rate limit value is exceeded, the maximum brake pressure for the towing vehicle brake system is limited, preferably in such a way that jackknifing is prevented.

[0079] Exceeding a yaw rate limit can indicate that the trailer is pushing so hard against the towing vehicle, especially when cornering, that the trailer threatens to push the rear end of the towing vehicle away in the transverse direction. Such lateral pushing of the rear end of the towing vehicle corresponds to an unstable driving situation, particularly jackknifing. Limiting the brake pressure of the towing vehicle's braking system when the yaw rate limit is exceeded can prevent this, thus maintaining driving stability.

[0080] In particular, the method according to the invention or an embodiment of the method can also be used for stabilization in the sense of yaw control, in which deceleration of the vehicle is not the primary goal, but rather the maintenance of driving stability.

[0081] The invention is explained in more detail below with reference to the accompanying drawings. They show:

[0082] Fig. 1 is a schematic representation of a vehicle combination which is designed to carry out an embodiment of the braking method;

[0083] Fig. 2 shows the pressure curve of a braking method from the prior art;

[0084] Fig. 3 shows the pressure curve of an embodiment of the braking method;

[0085] Fig. 4a an example of the pressure curve on the trailer brake system for discrete minimum friction coefficient zones;

[0086] Fig. 4b an example of the pressure curve on the trailer brake system as a function of the mass of the trailer combination for the minimum friction coefficient zone 3;

[0087] Fig. 5a an example of the pressure curve on the trailer brake system depending on the curve radius;

[0088] Fig. 5b shows an example of the limitation of the pressure curve on the towing vehicle brake system depending on the curve radius;

[0089] Fig. 6 illustrates the sequence of one embodiment of the braking method. Figure 1 shows a schematic representation of a vehicle combination 1 configured to perform one embodiment of the braking method. The vehicle combination 1 is formed by a towing vehicle 3 with a towing vehicle braking system 7 and a trailer 5 with a trailer braking system 9. The towing vehicle braking system 7 and the trailer braking system 9 together form the braking system 10 of the vehicle combination 1. The trailer 5 can also correspond to a semitrailer.

[0090] The towing vehicle braking system 7 is formed by brakes 41a of the towing vehicle 3 and a control unit 37a of the towing vehicle 3. The trailer braking system 9 is formed by brakes 41b of the trailer 5 and a control unit 37b of the trailer 5.

[0091] The control unit 37a of the towing vehicle 3 and the control unit 37b of the trailer 5 communicate with each other, for example, via TrailerCAN, as indicated by the double arrow between the control units 37a and 37b. The control units 37a and 37b can also be considered a single control unit 37 for the trailer combination.

[0092] It is also possible that only one control unit 37a is present in the towing vehicle 3, which is then regarded as control unit 37. This control unit 37 then controls both the towing vehicle braking system 7 and the trailer braking system 9, for example via pneumatic and / or hydraulic connections.

[0093] Trailer 5 does not have a functioning trailer ABS. This includes both a defective trailer ABS and a non-existent trailer ABS.

[0094] For example, trailer 5 does not have a functioning trailer ABS if no communication is possible between trailer 5 and towing vehicle 3, in particular between control units 37a and 37b. This can be the case if either the communication is faulty or trailer 5 is not set up for communication. Another possibility for a trailer 5 without a functioning trailer ABS is if only one-way communication originating from trailer 5 is possible. Another possibility for a trailer 5 without a functioning trailer ABS is if, although bilateral communication is possible between trailer 5 and towing vehicle 3, for example via CAN bus, trailer 5, in particular control unit 37b, reports a trailer ABS error.

[0095] A braking request 11 is detected by a brake pedal 21 and transmitted to the control unit 37a. The braking request 11 can also be issued by control units not shown, such as an ACC control unit. In particular, the braking request 11 does not have to be initiated by a driver, but can also be issued autonomously.

[0096] Furthermore, by means of a steering angle sensor 45, curve radius information 17 is sent to the control unit 37a as a function of the curve radius r detected by the steering angle sensor 45.

[0097] By means of a towing jaw with load cell 31, a coupling force 33 between trailer 5 and towing vehicle 3 is recorded and transmitted to the control unit 37a.

[0098] The actual longitudinal acceleration aLong and the actual lateral acceleration aLat of the trailer are recorded by an acceleration sensor 39 and transmitted to the control unit 37a.

[0099] Data from an outside temperature sensor 23, windscreen wiper sensor 47 / rain sensor 25, map / navigation information data 27, a speed v of the trailer 1, a yaw rate 35 and information about previous braking operations / previous minimum friction coefficient MFC determinations 29 are also sent to the control unit 37a.

[0100] A load sensor 43 detects the load state 15 of the trailer and transmits load state information 13 to the control unit 37b.

[0101] Through the communication between control units 37a and 37b, all information sent to the respective control units 37a and 37b is available in both control units 37a and 37b. Alternatively, only one control unit 37 can be provided, to which all of the above-mentioned data and information is available.

[0102] As explained further below with reference to Fig. 6, depending on the detected braking request 11, the actual longitudinal acceleration aLong, the actual lateral acceleration aLat, the load condition information 13, the curve radius information 17, the outside temperature sensor 23, the windscreen wiper sensor 47 / rain sensor 25, the map / navigation information data 27 and the previous braking operations / previous minimum friction coefficient MFC determinations 29, initial braking pressures pO, subsequent braking pressures pn and subsequent subsequent braking pressures pn+1 are applied to the brakes 41b of the trailer 5.

[0103] The follow-up brake pressures pn and subsequent follow-up brake pressures pn+1 are further dependent on a minimum friction coefficient MFC, which is determined taking into account at least the recorded actual longitudinal acceleration aLong and the actual lateral acceleration aLat.

[0104] Furthermore, depending on the coupling force 33 and the yaw rate 35, a maximum brake pressure p3 is applied to the brakes 41a of the towing vehicle, so that jackknifing in particular can be prevented.

[0105] Fig. 6 shows the sequence of an embodiment of the claimed braking method.

[0106] In a step S1, a braking request 11 is detected, which can originate from a driver and / or a (partially) autonomous system.

[0107] In a step S2, load condition information 13 of the trailer 1 is acquired, for example via load sensors, by means of a suspension or bellows pressure monitor, a tire pressure monitor, or force sensors. The load condition information 13 is taken into account when determining the follow-up brake pressure pn and / or when controlling the initial brake pressure pO, preferably analogously to the explanations for Fig. 4b. In a step S3, curve radius information 17 is acquired, for example, by means of a steering angle sensor 45. The curve radius information 17 is taken into account when determining the follow-up brake pressure pn and / or when controlling the initial brake pressure pO, preferably analogously to the explanations for Fig. 5a.

[0108] In a step S4, the initial brake pressure pO is applied to the trailer brake system 9, wherein, in addition to the load condition information 13 and curve radius information 17, the speed v of the trailer / trailer combination, data from an outside temperature sensor 23, in particular the outside temperature, data from a windscreen wiper sensor 47 / rain sensor 25, in particular about the presence of a wet road, map / navigation information data 27, in particular with information about the surface / road condition and information about previous braking operations / previous minimum friction coefficient MFC determinations 29 are taken into account when applying the initial brake pressure pO.

[0109] The more information available in step S4, the more precisely the initial brake pressure pO can be adapted to the actual road conditions. In detail, this means that the initial brake pressure pO can already be selected such that a certain braking performance is achieved while still preventing an unsafe driving condition, for example, due to the wheels of trailer 5 locking.

[0110] In a step S5, the resulting actual longitudinal acceleration aLong and actual lateral acceleration aLat of the vehicle combination 1 are recorded, for example by means of the acceleration sensor 39.

[0111] Subsequently, in a step S6, a minimum friction coefficient MFC is determined based on the recorded actual longitudinal acceleration aLong and the actual lateral acceleration aLat, preferably according to the formula where g is the acceleration due to gravity. In the event that curve radius information 17 indicates that a curve is being negotiated, a minimum friction coefficient MFC can be determined based on the actual lateral acceleration aLat resulting from cornering, which can also be taken into account when applying the initial brake pressure pO to the trailer brake system 9.

[0112] In a step S7, the follow-up brake pressure pn for the trailer brake system 9 is determined as a function of the minimum friction coefficient MFC. The assignment of different follow-up brake pressures pn to different minimum friction coefficients MFC can, for example, be carried out according to a predetermined assignment rule A within discrete intervals, as shown in Fig. 4a. The basic relationship is that the higher the minimum friction coefficient MFC, the higher the follow-up brake pressure pn can be selected.

[0113] In a step S8, the follow-up brake pressure pn is applied to the trailer brake system 9 in accordance with the brake request 11, which means that braking is only carried out as hard as requested.

[0114] It is then possible to return to step S5 again, so that steps S5 to S8 of the braking process are carried out repeatedly or continuously, whereby the follow-up brake pressure pn is considered in each case as the initial brake pressure pO of the subsequent follow-up brake pressure pn+1.

[0115] This creates an iterative process that approximates a maximum possible subsequent brake pressure pn+1. The maximum possible subsequent brake pressure pn+1 is reached when the actual longitudinal acceleration aLong, which results from the subsequent brake pressure pn, considered the initial brake pressure pO, no longer increases. Thus, the minimum friction coefficient MFC also does not increase further, and the resulting subsequent brake pressure pn+1 also remains constant at the maximum height.

[0116] In parallel or additionally, steps S9 and S10 are also performed during the repeated or continuous execution of steps S5 to S8. In a step S9, a coupling force 33 between trailer 5 and towing vehicle 3 is detected, for example, by means of the towing jaw with load cell 31. Once a coupling force limit value 34 is exceeded, the maximum brake pressure p3 for the towing vehicle braking system 7 is limited, preferably in such a way that jackknifing is prevented.

[0117] Step S10 takes place in parallel or in coordination with step S9, which is indicated by the double arrow between S9 and S10. In step S10, a yaw rate 35 of the towing vehicle 3 is detected, for example, by means of a yaw rate sensor in the towing vehicle. Once a yaw rate limit value 36 is exceeded, the maximum brake pressure p3 for the towing vehicle braking system 7 is limited, preferably in such a way that jackknifing is prevented.

[0118] The advantages of the method shown in Fig. 6 are explained in more detail with reference to Figs. 2 and 3.

[0119] Fig. 2 shows a pressure curve of a state-of-the-art braking system for a trailer without a functioning trailer ABS. The curve represents the pressure curve in the trailer braking system. The y-axis represents the pressure curve p, and the x-axis represents the time curve t.

[0120] In order not to endanger the driving safety and stability of the vehicle combination, the trailer is braked only with a greatly reduced pressure, in this case the level of the initial brake pressure pO, in the form of a stutter brake. This guarantees that the trailer wheels never lock. However, this significantly reduces the overall braking force of the vehicle combination, which in turn results in longer braking distances. Furthermore, in the method according to the prior art, the initial brake pressure pO cannot be selected based on additional information such as the curve radius information 17, the outside temperature sensor 23, the windshield wiper / rain sensor 25, the map / navigation information data 27 and / or the previous braking operations / previous minimum friction coefficient MFC determinations 29, so that it is generally lower. Fig. 3 shows the pressure curve on the trailer brake system 9 of an embodiment of the braking method claimed here.The axis labeling corresponds to that of Fig. 2. After a first pulse with the initial brake pressure pO, the pressure applied to the trailer brake system 9 increases to the follow-up pressure pn. This pressure is higher because the minimum friction coefficient MFC is determined using the method according to the invention, whereby locking of the trailer wheels is ensured at higher applied follow-up brake pressures pn. Thus, greater braking performance is achieved, which shortens the braking distance of the trailer / trailer combination 1 while simultaneously ensuring driving stability.

[0121] In the example shown in Fig. 3, the control of the follow-up pressures pn is pulsed, but this can also be done continuously.

[0122] Fig. 4a shows an example of the pressure curve applied to the trailer brake system for discrete minimum friction coefficient MFC zones Z1 - Z4. A pressure range is assigned to each specific minimum friction coefficient MFC zone Z1 - Z4.

[0123] If, for example, a low minimum friction coefficient MFC is determined based on the resulting actual longitudinal acceleration aLong and actual lateral acceleration aLat, the discrete minimum friction coefficient MFC zone Z1 is assigned to this, which only has a fixed pressure value.

[0124] For a slightly higher minimum friction coefficient MFC, the values ​​are assigned to zone Z2, whereby different pressure values ​​are possible within this zone Z2, for example depending on the charge state information 13 (see Fig. 4b) and / or the curve radius information 17 (see Fig. 5a).

[0125] The minimum friction coefficient MFC zones Z3 and Z4 also have a range of possible pressure values. In the present example, only pulsed pressure values ​​are applied within the minimum friction coefficient MFC zones Z1 - Z3. Within the minimum friction coefficient MFC zone Z4, a continuous pressure value of the corresponding level is applied. Within the minimum friction coefficient MFC zone Z4, the minimum friction coefficient MFC determined from the actual longitudinal acceleration aLong and the actual lateral acceleration aLat is so high that locking of the wheels of trailer 5 can be reliably ruled out, so that a continuously high brake pressure is applied.

[0126] Fig. 4b shows an example of the pressure curve applied to the trailer brake system 9 within the limits of the minimum friction coefficient zone 3 as a function of the mass m of the trailer combination.

[0127] The coefficient of friction, and thus the maximum transferable force between the wheels of the vehicle combination 1 and the road, depends heavily on the weight, i.e., the load acting on the respective wheels. The follow-up brake pressure pn can be higher in a loaded vehicle than in an unloaded vehicle. The same applies analogously to the initial brake pressure pO.

[0128] In the present example, the determined minimum friction coefficient was assigned to the minimum friction coefficient zone 3, whereby a medium mass is present within the minimum friction coefficient zone 3, so that ultimately the follow-up brake pressure of the level pn is applied to the trailer brake system 9.

[0129] Fig. 5a shows an example of the pressure curve applied to the trailer braking system 9 as a function of the curve radius information 17, in particular the curve radius r. In the present example, a curve radius r of more than 300 m is assumed to be straight-ahead driving.

[0130] When cornering, the trailer 1 is more susceptible to unstable driving situations such as the trailer swinging out of control, skidding, or jackknifing. Therefore, the follow-up brake pressure pn is controlled based on the curve radius information 17.

[0131] For example, the basic mechanism is designed analogously to Fig. 4b. Within a minimum friction coefficient zone, the follow-up brake pressure pn applied to the trailer brake system 9 can be determined according to Fig. 5a. For example, with a curve radius r of 225 m, the follow-up brake pressure pn is applied within the respective minimum friction coefficient zone. The same applies analogously to the initial brake pressure pO.

[0132] Fig. 5b shows an example of the percentage limitation of the pressure curve applied to the towing vehicle braking system 7 as a function of the curve radius r.

[0133] Since the follow-up brake pressure pn applied to the trailer brake system 9, depending on the determined minimum friction coefficient MFC, generally leads to a lower braking performance of the trailer brake system 9 compared to the braking performance of the towing vehicle brake system 7, the trailer 5 pushes onto the towing vehicle 7. The smaller the curve radius r, the greater the risk of jackknifing if the trailer 5 pushes onto the towing vehicle 7.

[0134] In order to prevent excessive pushing and the risk of jackknifing, particularly in curves, the maximum brake pressure p3 of the towing vehicle brake system 7 is limited as a function of the curve radius r.

[0135] The smaller the curve radius r, the higher the percentage limitation of the maximum brake pressure p3 of the towing vehicle brake system 7. In the present example, the curve radius is 225 m, so that the maximum brake pressure p3 of the towing vehicle brake system 7 is limited according to the graph shown in Fig. 5b.

[0136] Corresponding curves for the yaw rate or coupling force dependence of the towing vehicle brake system 9 pressure reduction can have an analogous or similar course.

[0137] This provides a safe and effective braking method for a trailer combination 1, especially in the event that no or no functioning trailer ABS is available. Reference symbol (part of the description)

[0138] 1 team

[0139] 3 towing vehicle

[0140] 5 followers

[0141] 7 Towing vehicle braking system

[0142] 9 Trailer braking system

[0143] 10 Braking system of the trailer

[0144] 11 Brake request

[0145] 13 Charge state information

[0146] 15 State of charge

[0147] 17 Curve radius information

[0148] 21 Brake pedal

[0149] 23 Outside temperature sensor

[0150] 25 Windscreen wiper sensor / rain sensor

[0151] 27 Map / Navigation Information Data

[0152] 29 previous braking operation / previous minimum friction coefficient MFC

[0153] 31 Drawbar with load cell

[0154] 33 Clutch force

[0155] 34 Clutch force limit

[0156] 35 Yaw rate

[0157] 36 Yaw rate limit

[0158] 37 Control unit

[0159] 37a Towing vehicle control unit

[0160] 37b Trailer control unit

[0161] 39 Accelerometer

[0162] 41 a Brakes towing vehicle

[0163] 41 b Brakes trailer

[0164] 43 charge sensors

[0165] 45 Steering angle sensor

[0166] 47 Windscreen wiper sensor pO Initial brake pressure pn Follow-up brake pressure pn+1 Subsequent brake pressure p3 Maximum brake pressure of the towing vehicle brake system

[0167] MFC minimum friction coefficient aLong actual longitudinal acceleration aLat actual lateral acceleration v speed of the vehicle combination r curve radius

[0168] A Allocation rule

[0169] Z1 MFC Zone 1

[0170] Z2 MFC Zone 2

[0171] Z3 MFC Zone 3

[0172] Z4 MFC Zone 4

[0173] At duration of a pressure pulse

[0174] D1 temperature signal

[0175] D2 Pig wiper signal

[0176] D3 Rain sensor signal

Claims

Patent claims 1 . Braking method for a combination (1), wherein the combination (1) is formed by a towing vehicle (3) with a towing vehicle braking system (7) and at least one trailer (5) with a trailer braking system (9), wherein the trailer braking system (9) does not have a functioning trailer ABS and the braking method comprises the following steps: - Detecting a braking request (11) (S1), - Control of an initial brake pressure (pO) to the trailer brake system (9) (S4), - Recording a resulting actual longitudinal acceleration (aLong) and an actual lateral acceleration (aLat) of the vehicle combination (1) (S5), - Determination of a minimum friction coefficient (MFC) taking into account the recorded actual longitudinal acceleration (aLong) and the actual lateral acceleration (aLat) (S6), - Determining a follow-up brake pressure (pn) for the trailer brake system (9) as a function of the minimum friction coefficient (MFC) (S7), - Control of the follow-up brake pressure (pn) to the trailer brake system (9) in accordance with the brake request (11) (S8).

2. Braking method according to claim 1, characterized in that the method is carried out repeatedly, preferably continuously, wherein in each case the subsequent brake pressure (pn) is regarded as the initial brake pressure (pO) of the subsequent subsequent brake pressure (pn+1).

3. Braking method according to one of the preceding claims, characterized in that the determination of the minimum friction coefficient (MFC) according to the formula where aLat is the actual lateral acceleration, aLong is the actual longitudinal acceleration and g is the acceleration due to gravity.

4. Braking method according to claim 2, further comprising the step - detecting a load condition information (13) of the combination (S2), wherein the load condition information (13) is additionally taken into account when determining the follow-up brake pressure (pn) and / or when controlling the initial brake pressure (pO), preferably such that the follow-up brake pressure (pn) and / or the initial brake pressure (pO) for the trailer brake system (9) is increased with increasing load condition (15).

5. Braking method according to one of the preceding claims, further comprising the step - detecting curve radius information (17) (S3), wherein the curve radius information (17) is additionally taken into account when determining the follow-up brake pressure (pn) and / or when controlling the initial brake pressure (pO), preferably in such a way that the follow-up brake pressure (pn) and / or the initial brake pressure (pO) for the trailer brake system (9) is reduced with decreasing curve radius (r).

6. Braking method according to claim 5, characterized in that a maximum brake pressure (p3) for the towing vehicle brake system (7) is limited as a function of the curve radius information (17), preferably in such a way that the maximum brake pressure (p3) for the towing vehicle brake system (7) is reduced with decreasing curve radius (r).

7. Braking method according to one of the preceding claims, characterized in that the initial brake pressure (pO) is controlled as a function of curve radius information (17), in particular as a function of a minimum friction coefficient (MFC) dependent on the actual lateral acceleration (aLat).

8. Braking method according to one of the preceding claims, characterized in that the step of controlling the initial brake pressure (pO) (S4) is carried out as a function of - the speed (v) of the combination (1 ) and / or - a temperature signal (D1) of an outside temperature sensor (23) and / or - a windscreen wiper signal (D2) of a windscreen wiper sensor (47) - and / or rain sensor signal (D3) of a rain sensor (25) and / or - map / navigation information data (27) and / or - previous minimum friction coefficient (MFC) determinations (29) are controlled.

9. Braking method according to one of the preceding claims, characterized in that the determination of the follow-up brake pressure (pn) for the trailer brake system (9) depending on the minimum coefficient of friction (MFC) and / or curve radius information (17) and / or load condition information (13) of the trailer (1) by means of a previously defined assignment rule (A), preferably at discrete intervals.

10. Braking method according to one of the preceding claims, characterized in that the initial brake pressure (pO) and / or the follow-up brake pressure (pn) is / are applied to the trailer brake system (9) for a limited time (At), preferably in a pulsed manner.

11. Braking method according to one of the preceding claims, further comprising the step - detecting a coupling force (33) between the trailer (5) and the towing vehicle (3) (S9), wherein, once a coupling force limit value (34) is exceeded, a maximum brake pressure (p3) for the towing vehicle brake system (7) is limited, preferably in such a way that jackknifing is prevented.

12. Braking method according to one of the preceding claims, further comprising the step - detecting a yaw rate (35) of the towing vehicle (3) (S10), wherein, once a yaw rate limit value (36) is exceeded, a maximum brake pressure (p3) for the towing vehicle brake system (7) is limited, preferably in such a way that jackknifing is prevented.

13. Control unit (37) for a braking system (10) of a vehicle combination (1), wherein the control unit (37) is configured to carry out a method according to one of claims 1 to 12.

14. A vehicle combination (1) comprising a towing vehicle (3) with a towing vehicle braking system (7) and at least one trailer (5) with a trailer braking system (9), as well as a control unit (37) according to claim 13 for carrying out a method according to one of claims 1 to 12.

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