METHOD FOR BRAKE CONTROL OF A VEHICLE TRUCK

Description

[0001] The invention relates to a method for brake control of a vehicle combination consisting of a towing vehicle with a hydraulic or pneumatic braking system and at least one attachable trailer with a pressure-controlled pneumatic braking system, in which an electronically controllable brake control valve arranged in the towing vehicle is used, which has at least two solenoid switching valves controllable by an electronic control unit, which are designed as an inlet valve and an outlet valve, wherein a brake control pressure can be generated by means of the brake control valve in a brake control line running from a brake control output of the brake control valve to a coupling head "brake" of the towing vehicle or to a trailer brake valve of the trailer and / or a coupling head "brake" at the rear of the trailer, and in which the current trailer status is determined by means ofwhether the towing vehicle is connected to a trailer and / or what the volume of the brake control line is.

[0002] To optimally control the braking of a vehicle combination, it is useful to know the current trailer status, i.e., whether at least one trailer is coupled or not. While it is possible to indirectly determine whether a trailer is coupled or not via the mandatory monitoring of the trailer's indicator lights at all trailer sockets, or directly by observing whether the trailer's electrical system is connected to the towing vehicle's electrical system via a plug connection (in the case of a specific configuration of two contacts in a 13-pin trailer socket), the electrical contacts of the trailer's plug and / or the towing vehicle's socket can be corroded or dirty, or the relevant signal wire can be broken somewhere. Therefore, an alternative method of determining the trailer's status is advantageous.

[0003] Furthermore, for optimal control of the braking process, it is necessary to know the volume of the brake control line running from the brake control output of the trailer control valve in the towing vehicle to the brake control input of the trailer brake valve in the trailer. This is essential to quickly build up a predetermined brake control pressure in the line for virtually instantaneous application of the trailer's wheel brakes. The trailer brake valve is usually located near the drawbar or fifth wheel and therefore relatively far forward, resulting in a relatively small volume of the brake control line.Since an agricultural tractor is permitted to tow up to two trailers, agricultural trailers are often equipped at their rear with a trailer coupling and two pneumatic coupling heads for attaching a second trailer and connecting its braking system. The brake control line of such a trailer runs from the respective coupling head to the coupling head of the towing vehicle, on one side to the trailer brake valve, and on the other side to the coupling head at the rear of the trailer, resulting in a comparatively large volume of brake control line.

[0004] In a method for brake control of a vehicle combination known from DE 10 2020 106 448 A1, it is provided that, to enable low-delay actuation of the wheel brakes of a coupled trailer, a pressure pulse exceeding the brake control pressure to be built up is introduced into the brake control line at the beginning of a braking process, whereby the magnitude and / or duration of the pressure pulse are determined depending on the calculated volume of the brake control line. The volume of the brake control line is determined after each new start-up of the towing vehicle by measuring the time interval of the pressure drop and / or the average pressure gradient during the pressure drop in the brake control line using sensors when the wheel brakes are released, and comparing these measurements with stored reference values.The system also detects whether a trailer is attached or not based on the measured volume of the brake control line. The magnitude and / or duration of the applied pressure pulse increases with increasing volume of the brake control line.

[0005] German patent DE 197 44 066 B4 describes a method for detecting trailer operation in a motor vehicle. In this method, when the brakes are applied, the pressure build-up in the brake control line leading to the trailer is measured by a sensor, and a characteristic parameter is determined from this measurement to identify trailer operation. This characteristic parameter is the pressure gradient during pressure build-up in the brake control line, which is then compared to a target pressure gradient defined by the application of the brake pedal in the towing vehicle. A downward deviation of the pressure gradient from the target pressure gradient indicates trailer operation, i.e., a coupled trailer.

[0006] From EP 2 918 469 B1, a device and a method for detecting a coupled trailer are known, in which, after the wheel brakes are released, the brake control pressure in the brake control line is sensorily detected in the brake control valve, which runs from the trailer control valve of the towing vehicle to the coupling head "brake" or to the trailer brake valve of a coupled trailer. The time interval until a predetermined pressure value is reached is determined from the brake control pressure profile during the pressure drop and compared with a predetermined time value. If the time interval of the pressure drop is less than the predetermined time value, an uncoupled trailer is detected. If the time interval of the pressure drop is equal to or greater than the predetermined time value, a coupled trailer is detected.

[0007] DE 10 2013 019 240 A1 relates to a method for detecting the operating states of a vehicle, in particular a state of the vehicle with or without a trailer. Specifically, a method for detecting an operating state of a vehicle is described, wherein the operating state is selected from at least one first or second operating state, in particular a state of the vehicle with or without a trailer, and the vehicle comprises a pneumatic braking system and a pneumatic control connection configured to connect the pneumatic braking system to another pneumatic braking system of a trailer. DE 199 55 798 A1 relates to a device for trailer identification that takes into account the specific characteristics of a vehicle combination consisting of a hydraulically braked towing vehicle and a pneumatically braked trailer.US 2022 / 048490 A1 relates to vehicle parking systems and is specifically directed to a parking brake device and a method for a vehicle propulsion unit, such as a semi-trailer tractor, to which a vehicle-towed unit, such as a truck trailer, can be connected.

[0008] The object of the invention is to present a method for brake control of a vehicle combination of the type mentioned at the outset, which provides at least one alternative possibility for determining the trailer status of a towing vehicle and the volume of the brake control line.

[0009] This problem is solved by methods having the features of independent claims 1, 6 and 11. The dependent claims define advantageous further developments of the methods.

[0010] Accordingly, the invention relates to a method for brake control of a vehicle combination consisting of a towing vehicle with a hydraulic or pneumatic braking system and at least one attachable trailer with a pressure-controlled pneumatic braking system, in which an electronically controllable brake control valve arranged in the towing vehicle is used, which has at least two solenoid switching valves controllable by an electronic control unit, which are designed as an inlet valve and an outlet valve, wherein a brake control pressure can be generated by means of the brake control valve in a brake control line running from a brake control output of the brake control valve to a coupling head "brake" of the towing vehicle or to a trailer brake valve of the trailer and / or a coupling head "brake" at the rear of the trailer, and in which the current trailer status is determined to ascertainwhether the towing vehicle is connected to a trailer and / or what the volume of the brake control line is.

[0011] To solve the aforementioned task, it is provided that a target pressure to be set in the brake control line is specified, that this target pressure is introduced into the brake control line by pulsed opening of the inlet valve and / or by pulsed opening of the outlet valve, that the brake control pressure in the brake control line is measured by sensors during pressure build-up, that a characteristic value for the trailer status of the towing vehicle and / or the line volume of the brake control line is determined from the pressure profile of the brake control pressure and / or the switching states of the inlet valve and / or the outlet valve until the target pressure is reached, and that this characteristic value is compared with at least one reference value previously determined as a function of the trailer status of the towing vehicle and / or the line volume of the brake control line and stored in a data memory of the control unit.and that, depending on the comparison result, the trailer status of the towing vehicle and / or the line volume of the brake control line are determined.

[0012] The invention therefore relates to a vehicle combination consisting of a towing vehicle with a hydraulic or pneumatic braking system and at least one attachable trailer with a pressure-controlled pneumatic braking system. In this vehicle combination, a brake control pressure can be applied via an electronically controlled brake control valve located in the towing vehicle, which has at least two solenoid valves controllable by an electronic control unit, namely an inlet valve and an outlet valve. This brake control pressure is applied to a brake control line running from a brake control output of the brake control valve to a coupling head ("brake") of the towing vehicle or to a trailer brake valve of the trailer and / or a coupling head ("brake") at the rear of the trailer.

[0013] By specifying a target pressure and controlling it by a pulse-like opening of the inlet valve and / or by a pulse-like opening of the outlet valve in the brake control line, a pressure increase in the brake control pressure and a plurality of switching states of the inlet valve and / or the outlet valve result until the target pressure is reached, with which at least one characteristic value can be determined that is characteristic of the trailer status of the towing vehicle and / or the line volume of the brake control line.

[0014] The trailer status indicates whether at least one trailer is coupled or whether no trailer is coupled. By comparing this value with at least one reference value, determined beforehand based on the trailer status of the towing vehicle and / or the volume of the brake control line and stored in a data memory of the control unit, the trailer status of the towing vehicle and / or the volume of the brake control line can be determined. The brake control line can be vented using opening pulses from the inlet valve and / or the outlet valve, which have a variable pulse width and / or a variable pulse interval. The pulse width is initially set relatively large and reduced as the brake control pressure approaches the target pressure.In contrast, the pulse interval is set relatively small at the beginning of the ventilation of the brake control line and increased as the brake control pressure approaches the target pressure.

[0015] According to the invention, the pulse widths PW IV, PWov of the opening pulses of the inlet valve and the outlet valve are determined until the target pressure pz is reached and each is added separately to a pulse width sum Σ PW IV of the inlet valve and to a pulse width sum Σ PWov of the outlet valve, that a pulse width sum difference Σ PW IV - Σ PWov is determined as a characteristic value by subtracting the pulse width sum Σ PWov of the outlet valve from the pulse width sum Σ PW IV of the inlet valve, and that the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line are determined by comparing the current pulse width sum difference Σ PW IV - Σ PWov with pulse width sum difference values ​​previously determined and stored as reference values ​​for different line volumes of the brake control line.

[0016] This first method variant, as well as the three methods described below, utilize the effect that the venting of the brake control line extends over a longer period until the target pressure is reached, specifically the longer the brake control line and the larger its volume. Accordingly, to reach the target pressure, opening pulses of the inlet valve with a larger pulse width and / or more opening pulses of the inlet valve are required, and / or the time until the target pressure is reached is longer the longer the brake control line and the larger its volume.

[0017] According to a first method variant, it is provided that the opening pulses P IV of the inlet valve and / or the opening pulses Pov of the outlet valve are determined until the target pressure pz is reached and summed to an opening pulse number n P as a characteristic value, and that by comparing the current opening pulse number with opening pulse number values ​​previously determined and stored as reference values ​​for different line volumes of the brake control line, the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line are determined.

[0018] According to a second method variant, the number of opening pulses PIV, Pov of the inlet valve and the outlet valve until the target pressure pz is reached is recorded and each is added separately to an opening pulse count Σn PIV of the inlet valve and an opening pulse count Σn POV of the outlet valve, respectively. By subtracting the opening pulse count Σn POV of the outlet valve from the opening pulse count Σn PIV of the inlet valve, a pulse count difference (Σn PIV - Σn POV) is determined as a characteristic value. By comparing the current pulse count difference Σn PIV - Σn POV with pulse count difference values ​​previously determined and stored as reference values ​​for different line volumes of the brake control line, the current trailer status of the towing vehicle and / or the current line volume VBC of the brake control line are determined.

[0019] One possible method variant provides that the time interval Δp Z until the target pressure pz is reached is determined and forms the characteristic value as the pressure build-up time, and that by comparing the current pressure build-up time Δp Z with pressure build-up time values ​​previously determined and stored as reference values ​​for different line volumes of the brake control line, the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line are determined.

[0020] In another variant of the process, the effect is exploited that pressure oscillations are excited in the air column of compressed air enclosed in the brake control line by the pulse-like opening of the inlet valve and / or by the pulse-like opening of the outlet valve, the number and amplitude of which differ depending on the length and the volume of the brake control line.Accordingly, this method variant provides that the number and / or the mean amplitude of pressure oscillations of the brake control pressure p BC until the target pressure pz is reached is recorded as a characteristic value number of oscillations ns and / or mean oscillation amplitude A S_m, and that by comparing the current number of oscillations ns and / or the current oscillation amplitude A S_m with previously determined and stored oscillation number values ​​and / or oscillation amplitude values ​​for different line volumes of the brake control line, the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line are determined.

[0021] According to a further development of the aforementioned procedure variants, it is provided that the trailer status with regard to an uncoupled trailer is recognized if the current characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m corresponds within a specified tolerance to a reference value determined without a coupled trailer, and that the trailer status with regard to a coupled trailer is recognized if the current characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m is greater than the reference value determined without a coupled trailer.

[0022] Furthermore, it may be provided that the line volume V BC of the brake control line is determined as the line volume of a brake control line running to the coupling head "brake", if the current characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m agrees within a specified tolerance with the reference value determined without a coupled trailer vehicle.

[0023] Furthermore, it may be provided that the line volume V BC of the brake control line is determined as the line volume of a reference value determined with a trailer attached, if the current characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m corresponds to the relevant reference value within a specified tolerance, or is determined by interpolation between two line volume values ​​from two reference values ​​determined with a trailer attached, if the current characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m lies between the two relevant reference values.

[0024] A process sequence independent of the embodiments mentioned so far also relates to a method for brake control of a vehicle combination consisting of a towing vehicle with a hydraulic or pneumatic braking system and at least one attachable trailer with a pressure-controlled pneumatic braking system, in which an electronically controllable brake control valve arranged in the towing vehicle is used, which has at least two solenoid switching valves controllable by an electronic control unit, which are designed as an inlet valve and an outlet valve, wherein a brake control pressure can be generated by means of the brake control valve in a brake control line running from a brake control output of the brake control valve to a coupling head "brake" of the towing vehicle or to a trailer brake valve of the trailer and / or a coupling head "brake" at the rear of the trailer.and in which the current trailer status is determined by checking whether the towing vehicle is connected to a trailer and / or the volume of the brake control line.

[0025] This method provides that a pneumatic pressure pulse is introduced into the brake control line with a defined opening duration Δt IV of the inlet valve, that the pressure pulse is introduced into the brake control line by a pulse-like opening of the inlet valve, that the brake control pressure p BC present in the brake control line after a predetermined time interval Δt P after the inlet valve has closed is determined by sensor as residual pressure Δp R, that the residual pressure Δp R is compared with at least one reference pressure value previously determined depending on the trailer status of the towing vehicle and / or the line volume of the brake control line and stored in a data memory of the control unit, and that, depending on the comparison result, the trailer status of the towing vehicle and / or the line volume V BC of the brake control line are determined.

[0026] This system utilizes the effect that the residual pressure remaining after a pressure pulse decreases with increasing length and correspondingly increasing volume of the brake control line. Therefore, it can be provided that the trailer status (i.e., that the trailer is not coupled) is detected when the current residual pressure Δp R is within a predefined tolerance of a reference pressure value determined without a trailer connected, and that the trailer status (i.e., that the trailer is coupled) is detected when the current residual pressure Δp R is lower than the reference pressure value determined without a trailer connected.

[0027] Furthermore, it may be provided that the line volume V BC of the brake control line is determined as the line volume of a brake control line running to the coupling head "brake" if the current residual pressure Δp R corresponds within a specified tolerance to the reference pressure value determined without a coupled trailer vehicle.

[0028] However, the line volume V BC of the brake control line is determined as the line volume of a reference pressure value determined with the trailer attached, if the current residual pressure Δp R corresponds to the relevant reference pressure value within a specified tolerance.

[0029] Furthermore, the line volume V BC of the brake control line can be determined by interpolation between two line volume values ​​from two reference pressure values ​​determined with the trailer attached, if the current residual pressure Δp R lies between the two relevant reference pressure values.

[0030] During a prolonged interruption of travel, the supply pressure in the supply lines of a towing vehicle and a trailer, as well as in the connected reservoirs, can drop due to leakage. This results in a relatively low supply pressure being available when the towing vehicle is restarted. Since the brake control line is vented from the towing vehicle's inlet supply line via the trailer control valve, setting the target pressure at low supply pressure requires inlet valve opening pulses with larger pulse widths and / or more opening pulses and / or a longer duration. Similarly, at low supply pressure, more pressure oscillations and / or pressure oscillations with higher or lower amplitudes can be generated in the brake control line, leading to a lower residual pressure in the brake control line after a pressure pulse is applied.

[0031] It is therefore advantageous if, in all the aforementioned methods and method variants for determining the current trailer status of the towing vehicle and / or for determining the current line volume V BC of the brake control line, the supply pressure p V currently present in a supply line of the towing vehicle is also measured, and that the comparison of the respective characteristic value Σ PW IV - Σ PW OV , n P , Δp Z , n S , A S_m or the residual pressure Δp R is carried out with reference values ​​or reference pressure values ​​previously determined and stored for the corresponding supply pressure pv.

[0032] To increase accuracy, it may also be possible to determine the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line by a combination of at least two of the aforementioned procedure variants.

[0033] The determination of the current trailer status of the towing vehicle and / or the current flow volume of the brake control line using the aforementioned procedure variants is carried out automatically according to another further development of the procedures, i.e. without the driver pressing the brake pedal, after each start-up of the towing vehicle, i.e. after the driver switches on the on-board power supply in the towing vehicle, and / or after each release of the parking brake in the towing vehicle by the driver.

[0034] The invention is further explained below with reference to exemplary embodiments illustrated in the accompanying drawing. The drawing shows Fig. 1 a brake control pressure profile over time and associated switching states of pulsedly opened and closed inlet and outlet valves during the control of a target pressure into a brake control line, Fig. 2in a diagram the values ​​of pulse width sum differences as a function of the conductor volumes of a brake control line, Fig. 3 a brake control pressure curve over time and associated switching states of a pulse-like opened and closed inlet valve during the control of a target pressure into a brake control line with an uncoupled trailer, Fig. 4 a brake control pressure curve over time and associated switching states of a pulse-like opened and closed inlet valve during the control of a target pressure into a brake control line with a coupled trailer vehicle, Fig. 5 a brake control pressure curve over time and associated switching states of a pulse-like opened and closed inlet valve during the control of a target pressure into a brake control line with an uncoupled trailer, Fig. 6a brake control pressure curve over time and associated switching states of a pulse-like opened and closed inlet valve during the control of a target pressure into a brake control line with a coupled trailer vehicle, Fig. 7 a brake control pressure curve over time during the application of a target pressure to a brake control line with the trailer uncoupled and coupled, with differently filled accumulators and a reservoir pressure in the towing vehicle of 4 × 10 5 < Pa, Fig. 8 a brake control pressure curve over time during the application of a target pressure to a brake control line with the trailer uncoupled and coupled, with differently filled accumulators and a reservoir pressure in the towing vehicle of 6 × 10 5 < Pa, Fig. 9a brake control pressure curve over time during the application of a pressure pulse to a brake control line with the trailer uncoupled and with the trailer coupled, as well as Fig. 10 a known trailer control valve for carrying out the procedure.

[0035] In the Fig. 10 An example shown is an electronically controllable trailer control valve 2 of a towing vehicle, which is known from the unpublished DE 10 2020 124 225.5 and is suitable for carrying out the brake control method of a vehicle combination described below. The vehicle combination shown there and also mentioned here consists of a towing vehicle with a hydraulic or pneumatic braking system and at least one attachable trailer with a pressure-controlled pneumatic braking system.

[0036] The trailer control valve 2 comprises a pneumatically controlled relay valve 10, a pneumatically controlled breakaway valve 16, an inlet valve 12, an outlet valve 14, and a pneumatic pressure sensor 18. The inlet valve 12 and the outlet valve 14 are each designed as a 2 / 2-way solenoid valve, by means of which the pneumatic control pressure applied to a control input 24 of the relay valve 10 can be adjusted. The switching solenoids of the inlet valve 12 and the outlet valve 14 are connected to an associated electronic control unit 8 via electrical control lines 20, and the pressure sensor 18 is connected to an associated electronic control unit 8 via electrical sensor lines 22.

[0037] The inlet valve 12 is closed when de-energized and open when energized. The outlet valve 14 is open when de-energized and closed when energized. A control pressure line 28, which runs from the outlet of the inlet valve 12 and from the inlet of the outlet valve 14 to a control input of the breakaway valve 16 and via a branch line 28a to the direct first control input 24 of the relay valve 10, can be connected via the inlet valve 12 to an internal supply pressure line 30 and via the outlet valve 14 to a vent line 32 leading to a vent outlet p3. A supply pressure line 30 is connected to a supply pressure input p11 of the trailer control valve 2.

[0038] In its installed state, the trailer control valve 2 has an external supply line from the towing vehicle's pneumatic compressed air supply system connected to the supply pressure inlet p11. This supply line carries a pressure of approximately 7.5 × 10⁵ Pa when the towing vehicle's engine is running. A line section 30a branching off from the supply pressure line 30 is routed via the cut-off valve 16 and an outlet-side line section 30b to a supply pressure outlet p21 of the trailer control valve 2. A coupling head "Supply" (red) 4 is connected to this supply pressure outlet p21 via an external supply pressure line 34. When the trailer is coupled, a supply pressure line 34' from the trailer is connected to the towing vehicle-side coupling head "Supply" 4 via a trailer-side coupling head "Supply" 4'. This supply line leads to a trailer brake valve and at least one reservoir of the trailer.

[0039] A supply pressure inlet of relay valve 10 is connected to the supply pressure line 30 via the branch line section 30a and the output line section 30b. A vent outlet of relay valve 10 is connected via a connecting line 32a to the vent line 32 leading to the vent outlet p3. A brake control output of relay valve 10 is connected via an output brake control line 36 to a brake control output p22 of the trailer control valve 2.

[0040] A coupling head "brake" (yellow) 6 is connected to the brake control output p22 via an external brake control line 42. When a trailer is coupled, a brake control line 42' of the trailer is connected to the towing vehicle-side coupling head "brake" 6 via a trailer-side coupling head "brake" 6', which leads to the trailer brake valve (not shown) of the trailer and, if present, to a coupling head "brake" located at the rear of the trailer for connecting the brake control line of a second trailer.

[0041] The pressure sensor 18 is connected to the output brake control line 36 via a sensor pressure line 38. A further control pressure line 40 is arranged between an inverted control pressure input p43 of the trailer control valve 2 and an inverted second control input 26 of the relay valve 10.

[0042] During braking, the electronic control unit 8 determines a target pressure pz from a braking value transmitted by a brake control unit of the towing vehicle. This target pressure is then set in the trailer control valve 2 by means of a pulsed opening of the inlet valve 12 and the outlet valve 14 by the relay valve 10 in the brake control line 42, 42'. When the trailer is coupled, the corresponding brake control pressure (p BC = p Z ) in the trailer brake valve of the trailer leads to the setting of a corresponding brake pressure for actuating the wheel brake cylinders of the trailer.

[0043] To optimally control the braking process of a vehicle combination, knowledge of the trailer status is useful, i.e., whether at least one trailer is coupled to the towing vehicle, or whether no trailer is coupled. Furthermore, when a trailer is coupled, knowledge of the flow volume of the brake control line 42, 42' running from the brake control output p22 of the trailer control valve 2 in the towing vehicle to the brake control input of the trailer brake valve in the trailer is required in order to quickly build up the specified brake control pressure (p BC = p Z ) in the brake control line 42, 42' for virtually instantaneous actuation of the trailer's wheel brakes.For example, in a method for brake control of a vehicle combination according to DE 10 2020 106 448 A1, it is provided that at the beginning of a braking process a pressure pulse exceeding the brake control pressure to be applied is introduced into the brake control line, the magnitude and / or duration of which are determined depending on the calculated line volume of the brake control line.

[0044] In the present method, it is generally provided that, preferably automatically after each start-up of the towing vehicle and / or after each release of the parking brake in the towing vehicle, a target pressure pz to be set in the brake control line 42, 42' is determined and specified; that this target pressure pz is introduced into the brake control line 42, 42' by pulse-like opening of the inlet valve 12 and / or the outlet valve 14; that the brake control pressure pBC in the brake control line 42, 42' is sensorially detected during pressure build-up; that from the pressure profile of the brake control pressure pBC and / or from the switching states of the inlet valve 12 and / or the outlet valve 14 until the target pressure pz is reached, a characteristic value for the trailer status of the towing vehicle and / or the line volume VBC of the brake control line 42, 42' is determined.that this characteristic value is compared with at least one reference value determined in advance depending on the trailer status of the towing vehicle and / or the line volume V BC of the brake control line 42, 42' and stored in a data memory of the control unit 8, and that depending on the comparison result the trailer status of the towing vehicle and / or the line volume V BC of the brake control line 42, 42' are determined.

[0045] A first method variant is shown in the diagrams of Fig. 1 and Fig. 2 illustrated. In the upper subdiagram (1a) of the Fig. 1 The curve of the brake control pressure pBC during pressure build-up from time t0 until the target pressure pz is reached at time tz is shown. In the lower subdiagram (1b) of the Fig. 1The switching states (0 = closed, 1 = open) of the inlet valve 12 and the outlet valve 14 are shown with different pulse widths PW IV for the inlet valve 12 and pulse widths PW OV for the outlet valve 14. The pulses for actuating the inlet valve 12 are drawn with solid lines and labeled IV = Inlet Valve. The pulses for actuating the outlet valve 14 are drawn with dashed lines and labeled OV = Outlet Valve. It can be seen that, with regard to the inlet valve 12, the first pulse width PW IV-1 is smaller than the second pulse width PW IV-2, and that the first pulse width PW IV-1 of the inlet valve 12 is larger than the third pulse width PW IV-3 through the sixth pulse width PW IV-6. The two pulse widths PW OV-1 and PW OV-2 for actuating the outlet valve 14 are each of equal length.

[0046] The Fig. 2The diagram shows a curve with reference values ​​R1, R2, R3, R4, R5, R6, R7, R8 determined in advance, for example during the development of the towing vehicle and the trailer, in the form of pulse width sum differences Σ PW IV - Σ PW OV as a function of the line volume V BC of a brake control line of the towing vehicle and the possibly coupled trailer.

[0047] To determine a characteristic value, the pulse widths PW IV , PWov of the opening pulses of the inlet valve 12 and the exhaust valve 14 are calculated according to Fig. 1The pulse width amplitudes (PWV) are determined until the target pressure pZ is reached, added separately to the pulse width sums ΣPWIV and ΣPWOV, and a pulse width sum difference ΣPWIV - ΣPWOV is determined as a characteristic value by subtraction. Subsequently, the current trailer status of the towing vehicle and the current line volume VBC of the brake control line 42, 42' are determined by comparing the current pulse width sum difference ΣPWIV - ΣPWOV with the previously determined and stored pulse width sum difference values ​​ΣPWIV - ΣPWOV for different line volumes VBC of the brake control line.

[0048] How Fig. 2As shown, the current pulse width amplitude difference Σ PW IV - Σ PW OV has an example value of 88 milliseconds (Σ PW IV - Σ PW OV = 88 ms). Since this value is greater than the reference value R1 determined beforehand for an uncoupled trailer (Σ PW IV - Σ PW OV = 77.5 ms), the trailer status is thus recognized, indicating that a trailer is coupled to the towing vehicle. Furthermore, the current pulse width amplitude difference Σ PW IV - Σ PW OV lies between the reference values ​​R5 and R6, which, through interpolation, leads to a current line volume V BC of the brake control line 42, 42' of V BC = 407.5 cm³.

[0049] A second procedural variant is in Fig. 3 and Fig. 4 illustrated in subdiagram 3a of the Fig. 3The time course of the brake control pressure pBC during pressure build-up from time t0 until the target pressure pz is reached at time tz is shown. In subdiagram 3b, the switching states (0 = closed, 1 = open) of the inlet valve 12 are shown with the trailer uncoupled. Fig. 4 The subdiagram 4a shows the time course of the brake control pressure p BC during the pressure build-up from time t 0 until the target pressure pz is reached at time tz, and the subdiagram 4b shows the switching states (0 = closed, 1 = open) of the inlet valve 12 with the trailer attached.

[0050] To determine a characteristic value, the required opening pulses P IV-1 to P IV-11 of the inlet valve 12 until the target pressure p Z is reached are summed to form an opening pulse count n P as a characteristic value. Subsequently, by comparing the current opening pulse count n P with previously determined and stored opening pulse count values ​​for various line volumes V BC of the brake control line, the current trailer status of the towing vehicle and the current line volume V BC of the brake control line 42, 42' are determined.

[0051] By comparing the Figures 3 and 4 It is evident that until the target pressure pz is reached, pressure is transferred to the brake control line 42, 42' with the trailer attached ( Fig. 4 ) significantly more opening pulses P IV are required than without a coupled trailer ( Fig. 3While seven opening pulses P IV-1 to P IV-7 of the inlet valve 12 are required to set the target pressure p Z without a trailer attached (n P = 7), eleven opening pulses P IV-1 to P IV-11 are required with a trailer attached (n P = 11). Analogous to the first method variant, the trailer status of an unattached trailer is also detected here if the current characteristic value, in this case the current number of opening pulses n P, corresponds within a predefined tolerance to a reference value determined without a trailer attached, and the trailer status of an attached trailer is detected if the current characteristic value, i.e., the current number of opening pulses n P, is greater than the reference value determined without a trailer attached.

[0052] The line volume VBC of the brake control line is determined as the line volume of the brake control line 42 running to the coupling head "brake" 6, if the current number of opening pulses nP corresponds within a specified tolerance to the reference value determined without a trailer attached. In contrast, the line volume VBC of the brake control line is determined as the line volume of a reference value determined with a trailer attached, if the current number of opening pulses nP corresponds within a specified tolerance to the relevant reference value, or determined by interpolation between two line volumes of two reference values ​​determined with a trailer attached, if the current number of opening pulses nP lies between the two relevant reference values.

[0053] A fourth method variant is shown in the diagrams of Fig. 5 and Fig. 6illustrated in subdiagram 5a of the Fig. 5 The diagram shows the time course of the brake control pressure pBC during pressure build-up from time t0 until the target pressure pz is reached at time tz. Subdiagram 5b of the Fig. 5 This shows the switching states (0 = closed, 1 = open) of the inlet valve 12 with the trailer uncoupled. Fig. 6 Part 6a shows the time course of the brake control pressure p BC during the pressure build-up from time t 0 until the target pressure p Z is reached at time tz, and part 6b shows the switching states (0 = closed, 1 = open) of the inlet valve 12 with the trailer attached.

[0054] To determine a key figure, according to the two Figures 5 and 6The time interval Δt Z until the target pressure pz is reached is determined in each case, which then forms the relevant characteristic value as the pressure build-up time. By comparing the current pressure build-up time Δt Z with previously determined and stored pressure build-up time values ​​for different brake control line volumes as reference values, the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line 42, 42' are determined.

[0055] By comparing the two Figures 5 and 6 It is evident that to build up the target pressure pz in the brake control line 42, 42' with the trailer attached ( Fig. 6 ) a significantly longer pressure build-up time Δt Z is required than without a coupled trailer vehicle ( Fig. 5Analogous to the first two method variants, it is also provided here that the trailer status of an uncoupled trailer is recognized if the current characteristic value, here the current pressure build-up time Δt Z, corresponds within a specified tolerance with a reference value determined without a coupled trailer, and that the trailer status of a coupled trailer is recognized if the current characteristic value, i.e. the current pressure build-up time Δt Z, is greater than the reference value determined without a coupled trailer.

[0056] The line volume VBC of the brake control line is determined as the line volume of the brake control line 42 running to the coupling head "brake" 6, if the current pressure build-up time ΔtZ corresponds within a specified tolerance to the reference value determined without a trailer attached. In contrast, the line volume VBC of the brake control line is determined as the line volume of a reference value determined with a trailer attached, if the current pressure build-up time ΔtZ corresponds within a specified tolerance to the relevant reference value, or determined by interpolation between two line volumes of two reference values ​​determined with a trailer attached, if the current pressure build-up time ΔtZ lies between the two relevant reference values.

[0057] With the diagrams of Figure 7 and 8The following illustrates the procedure sequence of a fifth variant. The diagrams show the time-dependent profiles of the brake control pressure pBC in the brake control line 42, 42', which is intended to reach a target pressure pZ of 1.7 × 10⁵ Pa. The diagrams depict the pressure profile in the brake control line 42, 42' with a dashed line without a trailer coupled to the towing vehicle. The pressure profile shown with a solid line shows the situation with a trailer coupled to the towing vehicle and an empty accumulator Sz in the towing vehicle, and the pressure profile shown with a dash-dotted line shows the situation with a coupled trailer and an empty accumulator SA in the trailer.

[0058] The one in Fig. 7The pressure curves shown were measured in a supply pressure line connected to the supply pressure inlet p11, in which a supply pressure of pV = 4 × 105 Pa prevails. The pressure curves shown in the Fig. 8 The pressure curves shown were determined with a supply pressure of pV = 6 × 105 Pa applied to the supply pressure inlet p11. By comparing the diagrams of the Figure 7 and 8 The influence of different supply pressures pv can be illustrated.

[0059] During a longer interruption of the journey, the supply pressure p V in the supply lines and the storage tanks connected to them of a towing vehicle and / or a trailer may drop due to leakage, so that when the towing vehicle is started up, a relatively low supply pressure p V is initially available, which delays the venting of the brake control line 42, 42' to the target pressure pz.

[0060] To determine a characteristic value suitable for determining the volume of the connected brake control line and for ascertaining whether a trailer is pneumatically connected to the towing vehicle, this method variant provides that the number and / or the mean amplitude of pressure oscillations of the brake control pressure p BC until the target pressure pz is reached is recorded as a number of oscillations ns and / or mean oscillation amplitude A S_m forming the characteristic value.

[0061] By comparing the current number of oscillations ns and / or the current oscillation amplitude A S_m with previously determined and stored oscillation number values ​​and / or oscillation amplitude values ​​for different line volumes of the brake control line, the current trailer status of the towing vehicle and / or the current line volume V BC of the brake control line 42, 42' are then determined.

[0062] The trailer status with regard to an uncoupled trailer is detected when the current number of vibrations (ns) and / or the current mean vibration amplitude AS_m are within a predefined tolerance and correspond to a reference value determined without a coupled trailer. The trailer status with regard to a coupled trailer is detected when the current number of vibrations (ns) and / or the current mean vibration amplitude AS_m are greater than the reference value determined without a coupled trailer.

[0063] The line volume V BC of the brake control line is determined as the line volume of the brake control line 42 running to the coupling head "brake" 6, if the current number of oscillations ns and / or the current mean oscillation amplitude A S_m corresponds within a specified tolerance to a reference value determined without a coupled trailer vehicle.In contrast, the line volume V BC of the brake control line is determined as the line volume of a reference value determined with a coupled trailer if the current number of oscillations ns and / or the current mean oscillation amplitude A S_m corresponds within a specified tolerance to the relevant reference value, or determined by interpolation between two line volumes of two reference values ​​determined with a coupled trailer if the current number of oscillations ns and / or the current mean oscillation amplitude A S_m lies between the two relevant reference values.

[0064] From the curves of the brake control pressure pBC in the diagrams of Fig. 7 and Fig. 8It is evident that the number of oscillations ns and the mean oscillation amplitude A S_m are greater with a coupled trailer than without a coupled trailer, and are also greater with empty storage tanks SZ, SA of the towing vehicle and the trailer than with only an empty storage tank Sz of the towing vehicle. A comparison of the diagram for the storage pressure p V = 4 × 10 5 < Pa according to Fig. 7 and the diagram for the storage pressure pV = 6 × 10⁵ < Pa according to Fig. 8 It also follows that the number of oscillations ns and the mean oscillation amplitude A S_m increase with increasing storage pressure pv.

[0065] In the diagram of Fig. 9A sixth method variant is illustrated, with the diagram showing the time profiles of a pressure pulse introduced into the brake control line 42, 42' with the trailer uncoupled (shown with a solid line) and with the trailer coupled (shown with a solid line). Comparing the two pressure profiles, it can be seen that after a time interval Δt P, a residual pressure Δp R is present with the trailer uncoupled, whereas no residual pressure is observed with the trailer coupled.

[0066] This method variant provides that a pneumatic pressure pulse is introduced into the brake control line 42, 42' of the inlet valve 12 with a defined opening duration Δt IV; that the pressure pulse is generated in the brake control line 42, 42' by a pulse-like opening of the inlet valve 12; that the brake control pressure p BC present in the brake control line 42, 42' after a predetermined time interval Δt P following the closing of the inlet valve 12 is measured by a sensor as residual pressure Δp R; that the residual pressure Δp R is compared with at least one reference pressure value previously determined as a function of the trailer status of the towing vehicle and / or the line volume of the brake control line 42, 42' and stored in a data memory of the control unit 8; and that, depending on the comparison result, the trailer status of the towing vehicle and / or the line volume V BC of the brake control line 42, 42' is determined. become.

[0067] The trailer status of an uncoupled trailer is recognized when the current residual pressure Δp R corresponds within a specified tolerance to a reference pressure value determined without a coupled trailer, and the trailer status of a coupled trailer is recognized when the current residual pressure Δp R is less than the reference pressure value determined without a coupled trailer.

[0068] The line volume VBC of the brake control line 42, 42' is determined as the line volume of the brake control line 42 extending to the coupling head "brake" 6 when the current residual pressure ΔpR corresponds within a specified tolerance to the reference pressure value determined without a trailer attached. In contrast, the line volume VBC of the brake control line 42, 42' is determined as the line volume of a reference pressure value determined with a trailer attached when the current residual pressure ΔpR corresponds within a specified tolerance to the relevant reference pressure value, or by interpolation between two line volumes of two reference pressure values ​​determined with a trailer attached when the current residual pressure ΔpR lies between the two relevant reference pressure values. Reference symbol (part of the description)

[0069] 2 Trailer control valve 4, 4' Coupling head "Supply" (red) 6, 6' Coupling head "Brake" (yellow) 8 Electronic control unit 10 Relay valve 12 Inlet valve, 2 / 2-way solenoid valve 14 Exhaust valve, 2 / 2-way solenoid valve 16 Breakaway valve 18 Pressure sensor 20 Control lines 22 Sensor lines 24 Direct control input 26 Inverted control input 28 Control pressure line 28a Line branch 30 Supply pressure line 30a, 30b Line sections 32 Vent line 32a Connection line 34, 34' Supply pressure line 36 Brake control line 38 Sensor pressure line 40 Control pressure line 42, 42' Brake control line A S_m Mean oscillation amplitude IV Inlet valve n P Number of opening pulses n P_IV Number of opening pulses of the inlet valve n P_OV Number of opening pulses of the outlet valve n S Number of oscillations OVOutlet Valve,Exhaust valve p 3 Vent outlet p 11 Supply pressure inlet p 21 Supply pressure outlet p 22 Brake control outlet p 43 Inverted control pressure inlet p BC Brake control pressure pv Supply pressure pz Target pressure P IV Inlet valve opening pulse P OV Exhaust valve opening pulse PW IV Pulse width of an inlet valve opening pulse PWov Pulse width of an exhaust valve opening pulse R1 - R8 Reference values ​​S Switching state of the inlet or outlet valve SA Trailer pressure accumulator SZ Towing vehicle pressure accumulator t Time t 0 Time at start of venting t Z Time at target pressure reached V BC Brake control line volume Δp R Residual pressure Δt IV Inlet valve opening duration Δt P Time span until residual pressure measurement Δt Z Time span until pressure build-up, pressure build-up time

Claims

1. Method for brake control of a vehicle combination which is made up of a tractor vehicle with a hydraulic or pneumatic braking system and at least one couplable trailer vehicle with a pressure-controlled pneumatic braking system, and in which an electronically controllable brake control valve (2) arranged in the tractor vehicle is used, which has at least two solenoid switching valves which can be actuated by an electronic control unit (8) and are designed as an inlet valve (12) and an outlet valve (14), wherein a brake control pressure (pBC) can be generated by means of the brake control valve (2) in a brake control line (42, 42') running from a brake control output (p22) of the brake control valve (2) to a "brake" coupling head (6) of the tractor vehicle or to a trailer brake valve of the trailer vehicle and / or a "brake" coupling head at the rear of the trailer vehicle, and in which, for ascertaining the current trailer status, it is established whether the tractor vehicle is connected to a trailer vehicle and / or how large the line volume(VBC) of the brake control line (42, 42') is, wherein a target pressure (pZ) to be set in the brake control line (42, 42') is specified, wherein this target pressure (pZ) is introduced into the brake control line (42, 42') by opening the inlet valve (12) in a pulsed manner and / or by opening the outlet valve (14) in a pulsed manner, wherein the brake control pressure (pBC) in the brake control line (42, 42') during the build-up of pressure is measured by sensor means, wherein a characteristic value which is characteristic of the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') is determined from the pressure profile with respect to time of the brake control pressure (pBC) and / or the profile with respect to time of the switching states of the inlet valve (12) and / or the outlet valve (14) until the target pressure (pZ) is reached, wherein this characteristic value is compared with at least one reference value ascertained in advance depending on the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') and stored in a data memory of the control unit (8), wherein the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') are determined depending on the comparison result, characterized in that the pulse widths (PWIV, PWOV) of the opening pulses of the inlet valve (12) and the outlet valve (14) are detected until the target pressure (pZ) is reached and in each case separately added to form a pulse width sum (Σ PWIV) of the inlet valve (12) and to form a pulse width sum (Σ PWOV) of the outlet valve (14), in that a pulse width sum difference (Σ PWIV - Σ PWOV) is determined as the characteristic value by subtracting the pulse width sum (Σ PWOV) of the outlet valve (14) from the pulse width sum (Σ PWIV) of the inlet valve (12), and in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') are / is determined by comparing the current pulse width sum difference (Σ PWIV - Σ PWOV) with stored pulse width sum difference values n ascertained in advance for different line volumes of the brake control line as reference values (R1, R2, R3, R4, R5, R6, R7, R8).

2. Method according to Claim 1, characterized in that the trailer status with respect to a non-coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to a reference value ascertained without a coupled trailer vehicle, and in that the trailer status with respect to a coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) is greater than the reference value ascertained without a coupled trailer vehicle.

3. Method according to either of Claims 1 and 2, characterized in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a brake control line (42) running to the "brake" coupling head (6) when the current characteristic value (∑ PWIV - Σ PWOV, nP, ΔpZ, nS, As_m) corresponds within a specified tolerance to the reference value ascertained without a coupled trailer vehicle, and in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a reference value ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to the reference value concerned, or is determined by interpolation between two line volume values of two reference values ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) lies between the two reference values concerned.

4. Method according to any of Claims 1 to 3, characterized in that, in order to ascertain the current trailer status of the tractor vehicle and / or the current line volume (VDC) of the brake control line (42, 42'), the supply pressure (pV) currently present in a supply line of the tractor vehicle is additionally measured, and in that the respective characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) or the residual pressure (ΔpR) is compared with stored reference values or reference pressure values ascertained in advance for the corresponding supply pressure (pV).

5. Method according to any of Claims 1 to 4, characterized in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') is ascertained automatically each time the tractor vehicle is started up and / or each time the parking brake in the tractor vehicle is released.

6. Method for brake control of a vehicle combination which is made up of a tractor vehicle with a hydraulic or pneumatic braking system and at least one couplable trailer vehicle with a pressure-controlled pneumatic braking system, and in which an electronically controllable brake control valve (2) arranged in the tractor vehicle is used, which has at least two solenoid switching valves which can be actuated by an electronic control unit (8) and are designed as an inlet valve (12) and an outlet valve (14), wherein a brake control pressure (pBC) can be generated by means of the brake control valve (2) in a brake control line (42, 42') running from a brake control output (p22) of the brake control valve (2) to a "brake" coupling head (6) of the tractor vehicle or to a trailer brake valve of the trailer vehicle and / or a "brake" coupling head at the rear of the trailer vehicle, and in which, for ascertaining the current trailer status, it is established whether the tractor vehicle is connected to a trailer vehicle and / or how large the line volume(VBC) of the brake control line (42, 42') is, wherein a target pressure (pZ) to be set in the brake control line (42, 42') is specified, wherein this target pressure (pZ) is introduced into the brake control line (42, 42') by opening the inlet valve (12) in a pulsed manner and / or by opening the outlet valve (14) in a pulsed manner, wherein the brake control pressure (pBC) in the brake control line (42, 42') during the build-up of pressure is measured by sensor means, wherein a characteristic value which is characteristic of the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') is determined from the pressure profile with respect to time of the brake control pressure (pBC) and / or the profile with respect to time of the switching states of the inlet valve (12) and / or the outlet valve (14) until the target pressure (pZ) is reached, wherein this characteristic value is compared with at least one reference value ascertained in advance depending on the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') and stored in a data memory of the control unit (8), wherein the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') are determined depending on the comparison result, characterized in that the opening pulses (PIV) of the inlet valve (12) and / or the opening pulses (POV) of the outlet valve (14) are ascertained until the target pressure (pZ) is reached and are summed to form a number of opening pulses (nP) as a characteristic value, and in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') are determined by comparing the current opening pulse number with stored opening pulse number values ascertained in advance for different line volumes of the brake control line as reference values.

7. Method according to Claim 6, characterized in that the trailer status with respect to a non-coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to a reference value ascertained without a coupled trailer vehicle, and in that the trailer status with respect to a coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) is greater than the reference value ascertained without a coupled trailer vehicle.

8. Method according to either of Claims 6 and 7, characterized in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a brake control line (42) running to the "brake" coupling head (6) when the current characteristic value (∑ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to the reference value ascertained without a coupled trailer vehicle, and in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a reference value ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to the reference value concerned, or is determined by interpolation between two line volume values of two reference values ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) lies between the two reference values concerned.

9. Method according to any of Claims 6 to 8, characterized in that, in order to ascertain the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42'), the supply pressure (pV) currently present in a supply line of the tractor vehicle is additionally measured, and in that the respective characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) or the residual pressure (ΔpR) is compared with stored reference values or reference pressure values ascertained in advance for the corresponding supply pressure (pV).

10. Method according to any of Claims 6 to 9, characterized in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') is ascertained automatically each time the tractor vehicle is started up and / or each time the parking brake in the tractor vehicle is released.

11. Method for brake control of a vehicle combination which is made up of a tractor vehicle with a hydraulic or pneumatic braking system and at least one couplable trailer vehicle with a pressure-controlled pneumatic braking system, and in which an electronically controllable brake control valve (2) arranged in the tractor vehicle is used, which has at least two solenoid switching valves which can be actuated by an electronic control unit (8) and are designed as an inlet valve (12) and an outlet valve (14), wherein a brake control pressure (pBC) can be generated by means of the brake control valve (2) in a brake control line (42, 42') running from a brake control output (p22) of the brake control valve (2) to a "brake" coupling head (6) of the tractor vehicle or to a trailer brake valve of the trailer vehicle and / or a "brake" coupling head at the rear of the trailer vehicle, and in which, for ascertaining the current trailer status, it is established whether the tractor vehicle is connected to a trailer vehicle and / or how large the line volume(VBC) of the brake control line (42, 42') is, wherein a target pressure (pZ) to be set in the brake control line (42, 42') is specified, wherein this target pressure (pZ) is introduced into the brake control line (42, 42') by opening the inlet valve (12) in a pulsed manner and / or by opening the outlet valve (14) in a pulsed manner, wherein the brake control pressure (pBC) in the brake control line (42, 42') during the build-up of pressure is measured by sensor means, wherein a characteristic value which is characteristic of the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') is determined from the pressure profile with respect to time of the brake control pressure (pBC) and / or the profile with respect to time of the switching states of the inlet valve (12) and / or the outlet valve (14) until the target pressure pZ) is reached, wherein this characteristic value is compared with at least one reference value ascertained in advance depending on the trailer status of the tractor vehicle and / or the line volume (VBC) of the brake control line (42, 42') and stored in a data memory of the control unit (8), wherein the trailer status of the tractor vehicle and / or the line volume VBC) of the brake control line (42, 42') are determined depending on the comparison result, characterized in that the number of opening pulses (PIV, POV) of the inlet valve (12) and the outlet valve (14) are detected until the target pressure (pZ) is reached and in each case separately added to form an opening pulse number (Σ nP_IV) of the inlet valve (12) and to form an opening pulse number (Σ nP_OV) of the outlet valve (14), in that a pulse number difference (Σ nP_IV - Σ nP_OV) is determined as the characteristic value by subtracting the opening pulse number (Σ nP_OV) of the outlet valve (14) from the opening pulse number (Σ nP_IV) of the inlet valve (12), and in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') are / is determined as reference values by comparing the current pulse number difference (Σ nP_IV - ∑ nP_OV) with stored pulse number difference values determined in advance for different line volumes of the brake control line.

12. Method according to Claim 11, characterized in that the trailer status with respect to a non-coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to a reference value ascertained without a coupled trailer vehicle, and in that the trailer status with respect to a coupled trailer vehicle is identified when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) is greater than the reference value ascertained without a coupled trailer vehicle.

13. Method according to either of Claims 11 and 12, characterized in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a brake control line (42) running to the "brake" coupling head (6) when the current characteristic value (∑ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to the reference value ascertained without a coupled trailer vehicle, and in that the line volume (VBC) of the brake control line (42, 42') is determined as the line volume of a reference value ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) corresponds within a specified tolerance to the reference value concerned, or is determined by interpolation between two line volume values of two reference values ascertained with a coupled trailer vehicle when the current characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) lies between the two reference values concerned.

14. Method according to any of Claims 11 to 13, characterized in that, in order to ascertain the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42'), the supply pressure (pV) currently present in a supply line of the tractor vehicle is additionally measured, and in that the respective characteristic value (Σ PWIV - Σ PWOV, nP, ΔpZ, nS, AS_m) or the residual pressure (ΔpR) is compared with stored reference values or reference pressure values ascertained in advance for the corresponding supply pressure (pV).

15. Method according to any of Claims 11 to 14, characterized in that the current trailer status of the tractor vehicle and / or the current line volume (VBC) of the brake control line (42, 42') is ascertained automatically each time the tractor vehicle is started up and / or each time the parking brake in the tractor vehicle is released.