METHOD FOR BRAKE CONTROL OF A VEHICLE COMBINATION

Abstract

A method is disclosed for controlling the brakes of a vehicle combination that includes a tractor vehicle and at least one trailer vehicle. A brake control valve in the tractor vehicle has magnetic switching valves that controlled by an electronic control unit, including an inlet valve and an outlet valve. To determine a current trailer status, it is determined whether the tractor vehicle is connected to a trailer vehicle and/or the line volume of the brake control line. A target pressure to be produced in the brake control line is specified and is produced by pulse-like opening of the inlet valve and/or the outlet valve. The brake control pressure in the brake control line is measured during the pressure build-up of pressure and a characteristic value for the trailer status and/or for the line volume of the brake control line is determined.

Claims

1-14. (canceled)

15. A method for controlling the brakes of a vehicle combination, the method comprising: providing a vehicle combination comprising: a tractor vehicle having a hydraulic or pneumatic brake system; at least one trailer vehicle configured to be coupled to the tractor vehicle and having a pressure-controlled pneumatic brake system; an electronic control unit (8); and an electronically controlled brake control valve (2) arranged in the tractor vehicle and comprising at least two magnetic switching valves that include an inlet valve (12) and an outlet valve (14), the at least two magnetic switching valves configured to be controlled by the electronic control unit (8); and a brake control line (42, 42) that runs from a brake control outlet (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; producing, by means of the brake control valve (2), a brake control pressure (p.sub.BC) in the brake control line (42, 42); determining a current trailer status of the tractor vehicle and/or a current line volume (V.sub.BC) of the brake control line (42, 42), thereby determining whether the tractor vehicle is connected to the at least one trailer vehicle and/or determining a line volume (V.sub.BC) of the brake control line (42, 42); specifying a target pressure (p.sub.Z) to be produced in the brake control line (42, 42); producing the target pressure (p.sub.Z) in the brake control line (42, 42) by pulse-like opening of the inlet valve (12) and/or by pulse-like opening of the outlet valve (14); measuring the brake control pressure (p.sub.BC) in the brake control line (42, 42) by sensor means during pressure build-up; determining, from a time variation of the brake control pressure (p.sub.BC) and/or a time variation of switching states of the inlet valve (12) and/or the outlet valve (14) until the target pressure (p.sub.Z) has been reached, a characteristic value for the trailer status of the tractor vehicle and/or the line volume (V.sub.BC) of the brake control line (42, 42); comparing the characteristic value with at least one reference value determined as a function of the trailer status of the tractor vehicle and/or as a function of the line volume (V.sub.BC) of the brake control line (42, 42), wherein the at least one reference value is stored in a data memory of the control unit (8); and determining the line volume (V.sub.BC) of the brake control line (42, 42) based on a result of comparing the characteristic value with the at least one reference value.

16. The method according to claim 15, comprising: detecting pulse widths (PW.sub.IV, PW.sub.OV) of the opening pulses of the inlet valve (12) and the outlet valve (14) until the target pressure (p.sub.Z) has been reached; adding the pulse widths (PW.sub.IV, PW.sub.OV) of the opening pulses of the inlet valve (12) and the outlet valve (14) to form a pulse width sum (? PW.sub.IV) for the inlet valve (12) and a pulse width sum (? PW.sub.OV) for the outlet valve (14); determining a pulse width sum difference (? PW.sub.IV?? PW.sub.OV) as a characteristic value by subtracting the pulse width sum (? PW.sub.OV) for the outlet valve (14) from the pulse width sum (? PW.sub.IV) for the inlet valve (12); comparing the pulse width sum difference (? PW.sub.IV?? PW.sub.OV) with previously determined values of the pulse width sum difference for various line volumes of the brake control line as reference values (R1, R2, R3, R4, R5, R6, R7, R8); and determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42).

17. The method according to claim 15, comprising: determining opening pulses (P.sub.IV) of the inlet valve (12) and/or (P.sub.OV) of the outlet valve (14) until the target pressure (p.sub.Z) has been reached; summing the opening pulses (P.sub.IV) of the inlet valve (12) and/or (P.sub.OV) of the outlet valve (14) until the target pressure (p.sub.Z) has been reached, to form a current opening pulse number (n.sub.P) as a characteristic value; comparing the current opening pulse number with previously determined values of the opening pulse number for various line volumes of the brake control line and stored as reference values; and determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42).

18. The method according to claim 15, comprising: detecting a number of opening pulses (P.sub.IV, P.sub.OV) of the inlet valve (12) and of the outlet valve (14) until the target pressure (p.sub.Z) has been reached; adding the number of opening pulses (P.sub.IV) of the inlet valve (12) to form an opening pulse number (?n.sub.P_IV) for the inlet valve (12); adding the number of opening pulses (P.sub.OV) of the outlet valve (14) to form an opening pulse number (? n.sub.P_OV) for the outlet valve (14); subtracting the opening pulse number (?n.sub.P_OV) for the outlet valve (14) from the opening pulse number (? n.sub.P_IV) for the inlet valve (12) to obtain a pulse number difference (? n.sub.P_IV?? n.sub.P_OV) as a characteristic value; comparing the pulse number difference (? n.sub.P_IV?? n.sub.P_OV) with previously determined values of the pulse number difference for various line volumes of the brake control line and stored as reference values; determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42).

19. The method according to claim 15, comprising: determining a time period (?p.sub.Z) until the target pressure (p.sub.Z) has been reached, as the pressure build-up time (?p.sub.Z), the pressure build-up time forming the characteristic value; comparing the pressure build-up time (?p.sub.Z) with previously determined values of the pressure build-up time for various line volumes of the brake control line and stored as reference values; and determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42).

20. The method according to claim 15, comprising: detecting a number and/or an average amplitude of pressure oscillations of the brake control pressure (p.sub.BC) until the target pressure (p.sub.Z) has been reached, as a reference-value-forming oscillation number (n.sub.S) and/or average oscillation amplitude (A.sub.S_m); comparing a current number (n.sub.S) of oscillations and/or the average oscillation amplitude (A.sub.S_m) with previously determined values of oscillation number and/or previously determined values of oscillation amplitude for various line volumes of the brake control line and stored as reference values; and determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42).

21. The method according to claim 15, comprising: determining that the current characteristic value (? PW.sub.IV?? PW.sub.OV, n.sub.P, ?p.sub.Z, n.sub.S, A.sub.S_m) matches the reference value within a specified tolerance; and recognizing a trailer status as not coupled for a trailer vehicle.

22. The method according to claim 21, comprising: determining the line volume (V.sub.BC) of the brake control line 42, 42) as the line volume of a brake control line (42) that extends as far as the Brake coupling head (6).

23. The method according to claim 15, comprising: determining that the current reference value (? PW.sub.IV?? PW.sub.OV, n.sub.P, ?p.sub.Z, n.sub.S, A.sub.S_m) is larger than the reference value; and recognizing a trailer status as coupled for a trailer vehicle.

24. The method according to claim 23, comprising: determining the line volume (V.sub.BC) of the brake control line (42, 42) as the line volume of a reference value determined when the trailer vehicle is coupled if the current reference value (? PW.sub.IV?? PW.sub.OV, n.sub.P, ?p.sub.Z, n.sub.S, A.sub.S_m), to within a specified tolerance, matches the reference value concerned or determining, by interpolation between two line volume values from reference values, that the current reference value (? PW.sub.IV?? PW.sub.OV, n.sub.P, ?p.sub.Z, n.sub.S, A.sub.S_m) is between two reference values concerned.

25. A method for controlling the brakes of a vehicle combination, the method comprising: providing a vehicle combination comprising: a tractor vehicle having a hydraulic or pneumatic brake system; at least one trailer vehicle configured to be coupled to the tractor vehicle and having a pressure-controlled pneumatic brake system; an electronically controlled brake control valve (2) arranged in the tractor vehicle, the electronically controlled brake valve comprising at least two magnetic switching valves that include an inlet valve (12) and an outlet valve (14), wherein the brake control valve (2) is configured to produce a brake control pressure (p.sub.BC) in a brake control line (42, 42) that runs from a brake control outlet (p22) of the brake control valve (2) as far as a Brake coupling head (6) of the tractor vehicle or as far as a trailer brake valve of the trailer vehicle and/or a Brake coupling head at the rear of the trailer vehicle; determining a current trailer status of whether the tractor vehicle is connected to the at least one trailer vehicle and/or determining a line volume (V.sub.BC) of the brake control line (42, 42); specifying a pneumatic pressure pulse to be produced in the brake control line (42, 42) with a fixed opening duration (?t.sub.IV) of the inlet valve (12); producing the pressure pulse in the brake control line (42, 42) by a pulse-like opening of the inlet valve (12); determining, by sensor means and after a specified time interval (?t.sub.P) after closing the inlet valve (12), a brake control pressure (p.sub.BC) in the brake control line (42, 42) as a residual pressure (?p.sub.R); comparing the residual pressure (?p.sub.R) with a reference pressure value determined beforehand as a function of the trailer status of the tractor vehicle and/or of the line volume of the brake control line and stored in a data memory of the control unit (8); and determining, based on a result of comparing the residual pressure, the current trailer status of the tractor vehicle and/or the line volume (V.sub.BC) of the brake control line (42, 42).

26. The method according to claim 25, comprising: determining that the residual pressure (?p.sub.R) matches a reference pressure value, within a specified tolerance, when no trailer vehicle is coupled to the tractor vehicle; and recognizing that the at least one trailer vehicle is coupled to the tractor vehicle.

27. The method according to claim 25, comprising: determining that the residual pressure (?p.sub.R) is lower than the reference pressure value when no trailer vehicle is coupled to the tractor vehicle; and recognizing that the at least one trailer vehicle is coupled to the tractor vehicle.

28. The method according to claim 25, comprising: determining that the residual pressure (?p.sub.R), to matches the reference pressure value, within a specified tolerance, determined when the at least one trailer vehicle is not coupled; and determining the line volume (V.sub.BC) of the brake control line (42, 42) as the line volume of a brake control line (42) that extends as far as the Brake coupling head (6).

29. The method according to claim 25, comprising: determining the line volume (V.sub.BC) of the brake control line (42, 42) as the line volume of the reference pressure value determined when a trailer vehicle is coupled; determining that the current residual pressure (?p.sub.R), to within a specified tolerance, matches the reference pressure value concerned, or determining by an interpolation between two line volumes from two reference pressure values determined when the at least one trailer vehicle is coupled, when the current residual pressure (?p.sub.R) is between the two reference pressure values concerned.

30. The method according to claim 25, comprising: determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42); measuring the supply pressure (p.sub.V) currently present in a supply line of the tractor vehicle; and comparing a respective characteristic value (? PW.sub.IV?? PW.sub.OV, n.sub.P, ?p.sub.Z, n.sub.S, A.sub.S_m) or a residual pressure (?p.sub.R) with stored reference values or with stored reference pressure values determined beforehand for the corresponding supply pressure (p.sub.V).

31. The method according to claim 25, wherein determining the current trailer status of the tractor vehicle and/or the current line volume (V.sub.BC) of the brake control line (42, 42) is/are determined automatically after every resumption of the operation of the tractor vehicle and/or after each release of the parking brake in the tractor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Below, the invention is described in greater detail with reference to the example embodiments illustrated in the attached drawing, which shows:

[0035] FIG. 1: A brake control pressure variation over time, and associated switching conditions of the pulse-like opening and closing of inlet valves and outlet valves during the production of a target pressure in a brake control line,

[0036] FIG. 2: In a diagram, the values of pulse width sum differences as a function of line volumes of a brake control line,

[0037] FIG. 3, including plots 3a and 3b: A brake control pressure variation over time, and associated switching conditions of a pulse-like opening and closing of an inlet valve during the production of a target pressure in a brake control line when no trailer vehicle is coupled,

[0038] FIG. 4, including plots 4a and 4b: A brake control pressure variation over time, and associated switching conditions of a pulse-like opening and closing of an inlet valve during the production of a target pressure in a brake control line when a trailer vehicle is coupled,

[0039] FIG. 5, including plots 5a and 5b: A brake control pressure variation over time, and associated switching conditions of a pulse-like opening and closing of an inlet valve during the production of a target pressure in a brake control line when no trailer vehicle is coupled,

[0040] FIG. 6, including plots 6a and 6b: A brake control pressure variation over time, and associated switching conditions of a pulse-like opening and closing of an inlet valve during the production of a target pressure in a brake control line when a trailer vehicle is coupled,

[0041] FIG. 7: A brake control pressure variation over time during the production of a target pressure in a brake control line, with an uncoupled and a coupled trailer vehicle, with storage containers filled to different extents and a supply pressure of 4?10.sup.5 Pa in the storage container of the tractor vehicle,

[0042] FIG. 8: A brake control pressure variation over time during the production of a target pressure in a brake control line, with an uncoupled and a coupled trailer vehicle, with storage containers filled to different extents and a supply pressure of 6?10.sup.5 Pa in the storage container of the tractor vehicle,

[0043] FIG. 9: A brake control pressure variation over time during the production of a pressure pulse in a brake control line, with an uncoupled and a coupled trailer vehicle, and

[0044] FIG. 10: A known trailer control valve for carrying out the method.

DETAILED DESCRIPTION

[0045] In FIG. 10 an electronically controlled trailer control valve 2 of a tractor vehicle is shown as an example, which is known from the previously unpublished DE 10 2020 124 225.5 and is suitable for carrying out the method for controlling the brakes of a vehicle combination described below. The vehicle combination shown therein and also mentioned here consists of a tractor vehicle with a hydraulic or pneumatic brake system and at least one trailer vehicle that can be coupled to it, with a pressure-controlled pneumatic brake system.

[0046] 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 in each case in the form of 2/2-way magnetic switching valves, by means of which a pneumatic control pressure applied at a control inlet 24 of the relay valve 10 can be produced.

[0047] The switching magnets of the inlet valve 12 and the outlet valve 14 are connected to an associated electronic control unit 8 by electrical control lines 20, and the pressure sensor 18 is connected thereto by electric sensor lines 22.

[0048] The inlet valve 12 is closed when not energized and open when energized. The outlet valve 14 is open when not energized and closed when energized. A control pressure line 28, which leads from the outlet of the inlet valve 12 and from the inlet of the outlet valve 14 to a control inlet of the breakaway valve 16 and via a line branch 28a to the direct first control inlet 24 of the relay valve 10, can be connected by way of the inlet valve 12 to an internal supply pressure line 30 and by way of the outlet valve 14 to a venting line 32 that leads to a venting outlet p3. A supply pressure line 30 is connected to a supply pressure inlet p11 of the trailer control valve 2.

[0049] In the installed condition of the trailer control valve 2, an external supply pressure line of a pneumatic compressed-air supply unit of the tractor vehicle is connected to the supply pressure inlet p11, which when the drive motor of the tractor vehicle is running, carries a supply pressure of around 7.5?10.sup.5 Pa. A line section 30a branching off from the supply pressure line 30 leads via the breakaway valve 16 and a line section 30b on the output side to a supply pressure outlet p21 of the trailer control valve 2. To this supply pressure outlet p21 is connected, via an external supply pressure line 34, a Supply coupling head (red) 4. When a trailer vehicle is coupled, to the Supply coupling head 4 on the tractor vehicle side there is connected a supply pressure line 34 of the trailer vehicle via a Supply coupling head 4 on the trailer side, which leads to a trailer brake valve and at least one storage container of the trailer.

[0050] A supply pressure inlet of the relay valve 10 is connected to the supply pressure line 30 by way of the branched line section 30a and the line section 30b on the outlet side. A venting outlet of the relay valve 10 is connected by way of a connecting line 32a to the venting line 32 that leads to the venting outlet p3. A brake control outlet of the relay valve 10 leads via a brake control line 36 on the outlet side to a brake control outlet p22 of the trailer control valve 2.

[0051] To the brake control outlet p22 is connected a Brake coupling head (yellow) 6 via an external brake control line 42. When a trailer vehicle is coupled, a brake control line 42 of the trailer is connected to the Brake coupling head 6 on the tractor vehicle side by way of a Brake coupling head 6 on the trailer side, which leads to the trailer brake valve (not shown) of the trailer vehicle and, if present, to a Brake coupling head positioned at the rear of the trailer vehicle for connecting the brake control line of a second trailer vehicle.

[0052] The pressure sensor 18 is connected by way of a sensor pressure line 38 to the brake control line 36 on the outlet side. A further control pressure line 40 is arranged between an inverted control pressure inlet p43 of the trailer control valve 2 and an inverted second control inlet 26 of the relay valve 10.

[0053] During a braking process, a target pressure p.sub.Z is determined in the electronic control unit 8 from a braking value communicated by a brake control unit in the tractor vehicle, which is then produced in the trailer control valve 2 by pulse-like opening and closing of the inlet valve 12 and the outlet valve 14 by means of the relay valve 10 in the brake control line 42, 42. When a trailer vehicle is coupled, the corresponding brake control pressure (p.sub.BC=p.sub.Z) in the trailer brake valve of the trailer vehicle leads to the production of a corresponding brake pressure for actuating the wheel-brake cylinders of the trailer vehicle.

[0054] To be able to control a braking process of a vehicle combination in an optimum manner, knowledge about the trailer status is useful, namely whether at least one trailer vehicle is coupled to the tractor vehicle or whether no trailer vehicle is coupled. In addition, for that purpose, when a trailer vehicle is coupled it is necessary to know the line volume of the brake control line 42, 42 that runs from brake control outlet 22 of the trailer control valve 2 in the tractor vehicle to the brake control inlet of the trailer control valve in the trailer vehicle, in order to be able to build up the specified brake control pressure (p.sub.BC=p.sub.Z) quickly in the brake control line 42, 42 for a largely delay-free actuation of the wheel brakes of the trailer vehicle. Thus, for example, in a method for controlling the brakes of a vehicle combination as described in DE 10 2020 106 448 A1, for this purpose it is provided that at the beginning of a braking process a pressure pulse higher than the brake control pressure to be produced is delivered into the brake control line, the level and/or the duration of which pulse depend(s) on the line volume of the brake control line determined.

[0055] In the above method it is generally provided that, preferably automatically, after every fresh operation of the tractor vehicle and/or after each releasing of the parking brake in the tractor vehicle, a target pressure p.sub.Z to be produced in the brake control line 42, 42 is determined and specified, and that the target pressure p.sub.Z is produced in the brake control line 42, 42 by pulse-like opening of the inlet valve 12 and/or the outlet valve 14, and that the brake control pressure p.sub.BC in the brake control line 42, 42 is detected by sensor means during the pressure build-up, and that from the variation of the brake control pressure and/or from the switching states of the inlet valve 12 and/or the outlet valve 14, until the target pressure p.sub.Z has been reached a characteristic value is determined for the trailer status of the tractor vehicle and/or for the line volume V.sub.BC of the brake control line 42, 42, and that this characteristic value is compared with at least one reference value determined beforehand as a function of the trailer status of the tractor vehicle and/or the line volume V.sub.BC of the brake control line 42, 42 and stored in a data memory of the control unit 8, and that depending on the result of the comparison the trailer status of the tractor vehicle and/or the line volume V.sub.BC of the brake control line 42, 42 is/are determined.

[0056] A first method variant is illustrated in the diagrams of FIG. 1 and FIG. 2. In the upper part-diagram (1a) of FIG. 1, the variation of the brake control pressure p.sub.BC during the pressure build-up is shown from time-point t.sub.0 until the target pressure p.sub.Z is reached at time-point t.sub.Z. In the lower part-diagram (1b) of FIG. 1, the switching states (0=closed, 1=open) of the inlet valve 12 and the outlet valve 14 are shown, with different pulse width sizes PW.sub.IV relating to the inlet valve 12 and PW.sub.OV relating to the outlet valve 14. The pulses for actuating the inlet valve 12 are shown by continuous lines and marked IV=Inlet Valve. The pulses for actuating the outlet valve 14 are shown by broken lines and marked OV=Outlet Valve. As regards the inlet valve 12, it can be seen that the first pulse width PW.sub.IV_1 is smaller than the second pulse width PW.sub.IV_2 and that the first pulse width PW.sub.IV_1 of the inlet valve 12 is larger than the third pulse width PW.sub.IV_3 to the sixth pulse width PW.sub.IV_6. The two pulse widths PW.sub.OV_1 and PW.sub.OV_1 for actuating the outlet valve 14 are each of the same length.

[0057] FIG. 2 shows in a diagram a curve with reference values R1, R2, R3, R4, R5, R6, R7, and R8 determined beforehand, for example during the development of the tractor vehicle and the trailer vehicle, in the form of pulse width sum differences ? PW.sub.IV?? PW.sub.OV as a function of the line volume V.sub.BC of a brake control line of the tractor vehicle and the trailer vehicle coupled thereto if there is one.

[0058] To determine a characteristic value, the pulse widths PW.sub.IV and PW.sub.OV of the inlet valve 12 and the outlet valve 14, shown in FIG. 1, until the target pressure p.sub.Z is reached are determined separately, added to form pulse width sums ? PW.sub.IV and ? PW.sub.OV, and the reference value is determined by subtraction to obtain a pulse width sum difference ? PW.sub.IV?? PW.sub.OV. Thereafter, by comparing the current pulse width sum difference ? PW.sub.IV?? PW.sub.OV with the pulse width sum differences ? PW.sub.IV?? PW.sub.OV determined beforehand for various line volumes V.sub.BC of the brake control line as reference values and stored, the current trailer status of the tractor vehicle and the current line volume V.sub.BC of the brake control line 42, 42 is/are determined.

[0059] A shown by FIG. 2, the current pulse width sum difference ? PW.sub.IV?? PW.sub.OV has, for example, a value of 88 milliseconds (? PW.sub.IV?? PW.sub.OV=88 ms). Since that value is larger than the reference value R1 (? PW.sub.IV?? PW.sub.OV=77.5 ms) determined beforehand for when no trailer vehicle is coupled, the trailer status determined is one in which a trailer vehicle is in fact coupled to the tractor vehicle. Furthermore, the current pulse width sum difference ? PW.sub.IV?? PW.sub.OV is between the reference values R5 and R6 which, by interpolation, gives a line volume V.sub.BC of the brake control line 42, 42 of V.sub.BC=407.5 cm.

[0060] A second method variant is illustrated in FIGS. 3 and 4, wherein the part-diagram 3a of FIG. 3 shows the time variation of the brake control pressure p.sub.BC during the pressure build-up between time-point to and time-point t.sub.Z when the target pressure p.sub.Z is reached. In the part-diagram 3b the switching states (0=closed, 1=open) of the inlet valve 12, respectively when no trailer vehicle is coupled, are shown. In FIG. 4, the part-diagram 4a shows the time variation of the brake control pressure p.sub.BC during the pressure build-up from time to until the target pressure p.sub.Z is reached at time t.sub.Z, while the part-diagram 4b shows the switching states (0=closed, 1=open) of the inlet valve 12, respectively, when a trailer vehicle is coupled.

[0061] To determine a characteristic value, the opening pulses P.sub.IV_1 to P.sub.IV_11 of the inlet valve 12 required until the target pressure p.sub.Z is reached are summed to form an opening-pulse number n.sub.P as a reference value. Thereafter, by a comparison of the current opening-pulse number with opening-pulse number values determined beforehand for various line volumes V.sub.BC of the brake control line and stored as reference values, the current trailer status of the tractor vehicle and the current line volume V.sub.BC of the brake control line 42, 42 are determined.

[0062] From a comparison of FIGS. 3 and 4 it can be seen that until the target pressure p.sub.Z in the brake control line 42, 42 is reached, when a trailer vehicle is coupled (FIG. 4) substantially more opening pulses P.sub.IV are needed than when no trailer vehicle is coupled (FIG. 3). Whereas with no coupled trailer vehicle seven opening pulses P.sub.IV_1 to P.sub.IV_7 of the inlet valve 12 are needed to produce the target pressure p.sub.Z(n.sub.P=7), to do this with a trailer vehicle coupled eleven opening pulses P.sub.V_1 to P.sub.IV_11 are needed (n.sub.P=11). Analogously to the first method variant, in this case it is also provided that when no trailer vehicle is coupled, this trailer status is recognized if the current characteristic value, in this case the current opening-pulse number n.sub.P, matches to within a specified tolerance a reference value determined with no coupled trailer, and that when a trailer vehicle is coupled, this trailer status is recognized if the current characteristic value, i.e. the current opening-pulse number n.sub.P is larger than the reference value determined when no trailer vehicle is coupled.

[0063] The line volume V.sub.BC of the brake control line is determined as the line volume of the brake control line 42 that extends as far as the Brake coupling head 6, if the current opening-pulse number n.sub.P matches, to within a specified tolerance, the reference value determined when no trailer vehicle is coupled. In contrast, the line volume V.sub.BC of the brake control line is determined as the line volume of a reference value determined when a trailer vehicle is coupled, if the current opening pulse number n.sub.P matches, to within a specified tolerance, the reference value determined when a trailer vehicle is coupled, or by an interpolation between two line volumes of two reference values determined when a trailer vehicle is coupled, if the current opening-pulse number n.sub.P is between the two reference values concerned.

[0064] A fourth method variant is illustrated in the diagrams of FIGS. 5 and 6, wherein the part-diagram 5a of FIG. 5 shows the time variation of the brake control pressure p.sub.BC during the pressure build-up from time to until the target pressure p.sub.Z is reached at time t.sub.Z. The part-diagram 5b of FIG. 5 shows the switching states (0=closed, 1=open) of the inlet valve 12 when no trailer vehicle is coupled. FIG. 6 shows in its part-diagram 6a the time variation of the brake control pressure p.sub.BC during the pressure build-up from time to until the target pressure p.sub.Z is reached at time t.sub.Z, and the part-diagram 6b shows the switching states (0=closed, 1=open) of the inlet valve 12 when a trailer vehicle is coupled.

[0065] To determine a characteristic value, according to the two FIGS. 5 and 6, the time period ?t.sub.Z until the target pressure t.sub.Z is reached is determined, which then, as the pressure build-up time, forms the relevant characteristic value. By comparing the current pressure build-up time ?t.sub.Z with pressure build-up times determined beforehand for various line volumes of the brake control line and stored as reference values, the current trailer status of the tractor vehicle and/or the current line volume V.sub.BC of the brake control line 42, 42 are determined.

[0066] By comparing the two FIGS. 5 and 6 it can be seen that to build up the target pressure p.sub.Z in the brake control line 42, 42 when a trailer vehicle is coupled (FIG. 6), a substantially longer pressure build-up time ?t.sub.Z is needed than when no trailer vehicle is coupled (FIG. 5). Analogous to the first two method variants, here too it is provided that the trailer status when no trailer vehicle is coupled can be recognized when the current characteristic value, in this case the current pressure build-up time ?t.sub.Z, matches to within a specified tolerance a reference value determined when no trailer vehicle is coupled, and the trailer status when a trailer vehicle is coupled is recognized when the current reference value, i.e., the current pressure build-up time ?t.sub.Z, is longer than the reference value determined when no trailer vehicle is coupled.

[0067] The line volume V.sub.BC of the brake control line is determined as the line volume of the brake control line 42 that extends s far as the Brake coupling head 6 when the current pressure build-up time ?t.sub.Z matches, to within a specified tolerance, the reference value determined when no trailer vehicle is coupled. In contrast, the line volume V.sub.BC of the brake control line is determined as the line volume when a trailer vehicle is coupled if the current pressure build-up time ?t.sub.Z matches, to within a specified tolerance, the reference value concerned, or is determined by an interpolation between two line volumes from two reference values determined when a trailer vehicle is coupled, if the current pressure build-up time ?t.sub.Z is between the two reference values concerned.

[0068] Below, with the diagrams of FIGS. 7 and 8 the process sequence of a fifth method variant is illustrated. The diagrams show in each case the time variations of the brake control pressure p.sub.BC in the brake control line 42, 42 which should reach a target pressure p.sub.Z equal to 1.7?10.sup.5 Pa. In the diagrams, broken lines show the pressure variation in the brake control line 42, 42 when no trailer vehicle is coupled to the tractor vehicle. The pressure variation shown by a continuous line shows the situation when a trailer vehicle is coupled to the tractor vehicle and the storage container S.sub.Z of the tractor vehicle is empty, and the pressure variation shown by a dot-dash line represents the situation when a trailer vehicle is coupled and the storage container S.sub.A of the trailer vehicle is empty.

[0069] The pressure variations shown in FIG. 7 were measured in a supply pressure line connected to the supply pressure inlet p11, in which there is a supply pressure of p.sub.V=4?10.sup.5 Pa. The pressure variations shown in FIG. 8 were determined at a supply pressure of p.sub.V=6?10.sup.5 Pa applied at the supply pressure inlet p11. By a comparison of the diagrams of FIGS. 7 and 8, the influence of different supply pressures p.sub.V can be made clear.

[0070] After a prolonged driving interruption, the supply pressure p.sub.V in the supply lines and the storage containers of a tractor vehicle and/or a trailer vehicle connected to them can fall due to leakage, so that when the traction vehicle begins operating again at first a relatively low supply pressure p.sub.V is available, owing to which the venting of the brake control line 42, 42 is delayed.

[0071] To determine a characteristic value suitable for determining the volume of the brake control line connected, and with which it can be established whether a trailer vehicle is pneumatically connected to the tractor vehicle, this method variant provides that the number and/or the average amplitude of pressure oscillations of the brake control pressure p.sub.BC until the target pressure p.sub.Z has been reached is detected as a number of oscillations n.sub.S and/or an average oscillation amplitude A.sub.S_m that forms the characteristic value.

[0072] By comparing the current number of oscillations n.sub.S and/or the current oscillation amplitude A.sub.S_m with oscillation number values and/or oscillation amplitude values determined beforehand and stored for various line volumes of the brake control line as reference values, the current trailer status of the tractor vehicle and/or the current line volume V.sub.BC of the brake control line 42, 42 are determined.

[0073] The trailer status as regards an uncoupled trailer vehicle is recognized if the current number of oscillations n.sub.S and/or the current average oscillation amplitude A.sub.S_m matches, to within a specified tolerance, a reference value determined when no trailer vehicle is coupled. The trailer status as regards a coupled trailer vehicle is recognized if the current oscillation number n.sub.S and/or the current oscillation amplitude A.sub.S_m is larger than the reference value determined when no trailer vehicle is coupled.

[0074] The line volume V.sub.BC of the brake control line is determined as the line volume of the brake control line 42 extending as far as the Brake coupling head 6, when the current number of oscillations n.sub.S and/or the current average oscillation amplitude A.sub.S_m match, to within a specified tolerance, a reference value determined when no trailer vehicle is coupled. In contrast, the line volume V.sub.BC of the brake control line is determined as the line volume from a reference value determined when a trailer vehicle is coupled if, to within a specified tolerance, the current oscillation number n.sub.S and/or the current average oscillation amplitude A.sub.S_m match the reference value concerned, or is determined by interpolation between two line volumes from two reference values determined when the current oscillation number n.sub.S and/or the current average oscillation amplitude A.sub.S_m is between the two reference values concerned.

[0075] From the curve shapes of the brake control pressure p.sub.BC in the diagrams of FIG. 7 and it is evident in both cases that the oscillation number n.sub.S and the average oscillation amplitude A.sub.S_m when a trailer vehicle is coupled are larger than when no trailer vehicle is coupled, and are larger with empty storage containers S.sub.Z, S.sub.A of both the tractor vehicle and the trailer vehicle than with an empty storage container S.sub.Z of the tractor vehicle alone. By comparing the diagram for the supply pressure p.sub.V=4?10.sup.5 Pa in FIG. 7 with the diagram for the supply pressure p.sub.V=6?10.sup.5 Pa in FIG. 8, it can also be seen that the oscillation number n.sub.S and the average oscillation amplitude A.sub.S_m increase with increasing supply pressure p.sub.V.

[0076] The diagram of FIG. 9 illustrates a sixth method variant, wherein the diagram contains the time variation of a pressure pulse produced in the brake control line 42, 42 when no trailer vehicle is coupled (shown by a broken line) and with a trailer vehicle coupled (shown by a continuous line). By comparing the two pressure variations it can be seen that after a time period ?t.sub.P when no trailer vehicle is coupled there is a residual pressure ?p.sub.R, whereas in contrast when a trailer vehicle is coupled there is no residual pressure.

[0077] This method variant provides that a pneumatic pulse to be produced in the brake control line 42, 42 with a fixed opening duration ?t.sub.IV of the inlet valve 12 is specified, and that the pressure pulse is produced in the brake control line 42, 42 by a pulse-like opening of the inlet valve 12, and that the brake control pressure p.sub.BC present in the brake control line 42, 42 after a specified time interval ?t.sub.P is measured by sensor means as a residual pressure ?p.sub.R, and that the residual pressure ?.sub.PR is compared with a reference value determined beforehand as a function of the trailer status of the tractor vehicle and/or of the line volume of the brake control en 42 and stored in a data memory of the control unit 8, and that depending on the result of the comparison the trailer status of the tractor vehicle and/or the line volume V.sub.BC of the brake control line 42, 42 is/are determined.

[0078] The trailer status when no trailer vehicle is coupled is recognized if the current residual pressure ?p.sub.R, to within a specified tolerance, matches a reference pressure value determined when no trailer vehicle is coupled, and the trailer status when a trailer vehicle is coupled is recognized if the current residual pressure ?p.sub.R is lower than the reference pressure value determined when no trailer vehicle is coupled.

[0079] The line volume V.sub.BC of the brake control line 42, 42 is determined as the line volume of the brake control line 42 that extends as far as the Brake coupling head 6 when the current residual pressure ?p.sub.R, to within a specified tolerance, matches the reference pressure value determined when no trailer vehicle is coupled. In contrast, the line volume V.sub.BC of the brake control line 42, 42 is determined as the line volume of a reference pressure value when a trailer vehicle is coupled, if the current residual pressure ?p.sub.R, to within a specified tolerance, matches the reference pressure value concerned, or is determined by an interpolation between two line volumes of two reference pressure values determined when a trailer vehicle is coupled if the current residual pressure ?p.sub.R is between the two reference pressure values concerned.

INDEXES

[0080] 2 Trailer control valve [0081] 4, 4 Supply coupling head (red) [0082] 6, 6 Brake coupling head (yellow) [0083] 8 Electronic control unit [0084] 10 Relay valve [0085] 12 Inlet valve, 2/2-way magnetic valve [0086] 14 Outlet valve, 2/2-way magnetic valve [0087] 16 Breakaway valve [0088] 18 Pressure sensor [0089] 20 Control lines [0090] 22 Sensor lines [0091] 24 Direct control inlet [0092] 26 Inverted control inlet [0093] 28 Control pressure line [0094] 28a Line branch [0095] 30 Supply pressure line [0096] 30a, 30b Line sections [0097] 32 Venting line [0098] 32a Connecting line [0099] 34, 34 Supply pressure line [0100] 36 Brake control line [0101] 38 Sensor pressure line [0102] 40 Control pressure line [0103] 42, 42 Brake control line [0104] A.sub.S_m Average oscillation amplitude [0105] IV Inlet valve [0106] n.sub.P Number of opening pulses [0107] n.sub.P_IV Number of opening pulses of the inlet valve [0108] n.sub.P_OV Number of opening pulses of the outlet valve [0109] n.sub.S Number of oscillations [0110] OV Outlet valve [0111] p.sub.3 Venting outlet [0112] p.sub.11 Supply pressure inlet [0113] p.sub.21 Supply pressure outlet [0114] p.sub.22 Brake control outlet [0115] p.sub.43 inverted control pressure inlet [0116] p.sub.BC Brake control pressure [0117] p.sub.V Supply pressure [0118] p.sub.Z Target pressure [0119] P.sub.IV Opening pulse of the inlet valve [0120] P.sub.OV Opening pulse of the outlet valve [0121] PW.sub.IV Pulse width of an opening pulse of the inlet valve [0122] PW.sub.OV Pulse width of an opening pulse of the outlet valve [0123] R1-R8 Reference values [0124] S Switching state of the inlet or outlet valve [0125] S.sub.A Pressure reservoir of the trailer [0126] S.sub.Z Pressure reservoir of the tractor vehicle [0127] t Time [0128] t.sub.o Time-point at the start of venting [0129] t.sub.Z Time-point when the target value is reached [0130] V.sub.BC Line volume of the brake control line [0131] ?p.sub.R Residual pressure [0132] ?t.sub.V Opening duration of the inlet valve [0133] ?t.sub.P Time interval until residual pressure measurement [0134] ?t.sub.Z Time interval until pressure build-up, pressure build-up time