METHOD FOR BRAKE CONTROL OF A TRAINS

Description

[0001] The invention relates to a method for braking control of a vehicle combination consisting of a towing vehicle and a trailer, wherein the towing vehicle has a pneumatic / hydraulic towing vehicle braking system and the trailer vehicle has a pneumatic / hydraulic trailer braking system. The method comprises an electrically controllable trailer control valve, which is assigned at least one trailer control valve characteristic curve stored in an electronic control device for controlling a trailer braking pressure of the trailer braking system for normal operation of the vehicle combination. Furthermore, the invention relates to a vehicle combination designed and equipped in such a way that the aforementioned method can be operated thereon.

[0002] When a vehicle combination is braked, the brake pressure on the trailer's brakes can be regulated using an electrically controlled trailer control valve. Such a trailer control valve can be controlled according to a characteristic curve that establishes a fixed, for example, largely linear, relationship between the tractor brake pressure and the trailer brake pressure. This trailer control valve characteristic curve is typically used for all operating situations.

[0003] The brake coordination between the towing vehicle and trailer is regulated by a standard that contains so-called compatibility bands, which define a relationship between the braking force and the pressure at the coupling head of the towing vehicle. However, for some vehicle combinations, such as agricultural vehicle combinations, other off-highway vehicle combinations, or trucks for heavy and special transport, this brake coordination is often problematic, as such combinations of towing vehicle and trailer can have very different masses in use and the coupling force between the vehicles can fluctuate considerably. If a vehicle combination also has a hydrostatic continuously variable automatic transmission, the vehicle combination can be decelerated significantly simply by changing the transmission ratio, for example by operating a control lever or releasing the accelerator, without the service brake having to be applied.The same applies to active engine or continuous braking.

[0004] If the service brake is not applied, such a deceleration results in the trailer not being braked and thus pushing itself onto the towing vehicle without braking. Incorrect brake adjustment may result in the actual braking in such special driving conditions not corresponding to the required braking within the compatibility bands. This can lead to excessive coupling forces between the towing vehicle and trailer, and subsequently to instability of the vehicle combination. In particular, a potentially dangerous jackknifing of the vehicle combination, known as "jackknifing," is feared in critical driving situations.

[0005] DE 44 38 252 A1 discloses a method for adapting the braking of a trailer to a towing vehicle. US 2014 / 343813 A1 discloses a method for preventing so-called "jack-knifing." EP 1 820 708 A2 discloses a hydraulic arrangement for braking a trailer. DE 10 2014 006 671 A1 discloses a method and a system for stabilizing a vehicle combination. EP 2 384 941 A1 discloses a braking method and a braking system for a power-braked device.

[0006] DE 42 43 245 A1 describes a coupling force control system for a vehicle combination. The coupling force between a towing vehicle and a trailer is determined and adjusted to a target coupling force. This is intended to ensure stability-optimized braking of a vehicle combination at all operating points.

[0007] From DE 10 2013 103 068 A1 a method is known in which a trailer brake of a vehicle combination is automatically activated if, when the friction brake of the towing vehicle is not actuated, a deceleration of the trailer vehicle is detected which exceeds a predetermined limit value.

[0008] DE 10 2014 100 069 A1 discloses a method for controlling a braking system of a towing vehicle-trailer combination, wherein the towing vehicle has, for example, a continuously variable transmission. An electronic control unit comprising a vehicle control unit and an electro-pneumatic trailer control valve detects a trailer pushing onto the towing vehicle in a driving state with the service brake not applied. When a predetermined thrust of the trailer is reached or exceeded, the control unit automatically activates a braking system of the trailer to generate a braking force when the service brake of the towing vehicle is not applied. The control unit detects the reaching or exceeding of the predetermined thrust of the trailer when a parameter has reached, exceeded, or fallen below a predetermined limit value assigned to it.One parameter used is the drive torque generated by a prime mover of the towing vehicle, for example, the torque at a crankshaft and / or the output torque at at least one driven wheel of the towing vehicle. The drive or output torque is monitored to determine whether it falls below a predetermined torque limit, as this would result in deceleration of the towing vehicle.

[0009] Against this background, the object of the invention was to propose a method for braking control of a vehicle combination by means of which reliable braking of a trailer is ensured in all deceleration situations of the vehicle combination, and by means of which comfortable braking coordination between the towing vehicle and the trailer is simultaneously achieved. In particular, improved and more harmonious braking coordination is to be achieved for off-highway vehicle combinations, such as an agricultural tractor-trailer combination or semi-trailer trucks or bridge trucks for special transport, which can be subject to large coupling forces and spontaneous, strong vehicle decelerations due to the operation of a continuously variable automatic transmission in the drive train, an engine brake, a continuous brake, and / or a significantly different mass distribution between the towing vehicle and the trailer.

[0010] This object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments are defined in the dependent claims.

[0011] The invention was based on the discovery that, in a vehicle combination consisting of a towing vehicle and a trailer, better braking coordination between the two vehicles can be achieved if, instead of a fixed trailer control valve characteristic curve, variable characteristic curves are used to control the brakes of the trailer. Relevant parameters should be taken into account in each case. This makes it possible to apply and vary the trailer brake pressure in such a way that the trailer can quickly counteract the jackknifing and the described behavior. This is particularly true when, for example, spontaneous vehicle deceleration occurs due to adjusting a gear ratio or activating an engine or continuous brake, or when, due to a large trailer mass in an agricultural application, high and fluctuating coupling forces act between the vehicles.This makes it easier to always maintain the compatibility bands of the brake tuning.

[0012] The invention is therefore based on a method for braking control of a vehicle combination consisting of a towing vehicle and a trailer vehicle, wherein the towing vehicle has a pneumatic / hydraulic towing vehicle braking system and the trailer vehicle has a pneumatic / hydraulic trailer braking system, with an electrically controllable trailer control valve, to which at least one trailer control valve characteristic curve stored in an electronic control device is assigned for controlling a trailer braking pressure of the trailer braking system for normal operation of the vehicle combination.

[0013] To achieve the stated object, the invention provides that the trailer control valve characteristic curve stored for the normal operation of the vehicle combination is varied or replaced by a trailer control valve characteristic curve for a special operation when a special operation of the vehicle combination that deviates from the normal operation or is assessed as potentially inadmissible is detected or predicted, taking into account parameters relevant to this situation.

[0014] Normal operation of the vehicle combination is understood to mean a driving operation in which, when the vehicle combination decelerates due to the actuation of a braking system of the towing vehicle, the brake pressure of the trailer is controlled by means of a trailer control valve characteristic curve stored for this operation.

[0015] The method according to the invention is based on the fact that the trailer's braking system is actuated in a special operating situation with a brake pressure that is varied using a characteristic curve that is particularly suitable for this situation. This achieves safe and comfortable braking of the trailer. This type of brake control is made possible by an electrically controlled trailer control valve, as is already present in many vehicle combinations. Existing sensor devices in the drive train of the vehicle combination can be used to implement the method, if available. Additional sensor devices are available on the market and can expand the system as needed. An existing electronic control device only needs to be adapted with regard to its computing algorithms for controlling an electrically controllable trailer control valve and, if necessary, with regard to its memory capacity for storing characteristic curve data.At this point it should be noted that the control characteristics or characteristic curve data in the electronic control device are, to put it simply, stored in the form of tables or value pairs.

[0016] During normal operation of the vehicle combination, the use of a trailer control valve characteristic curve for brake control can preferably be provided, as before, which maps a curve of a towing vehicle brake pressure of the towing vehicle brake system in relation to a trailer brake pressure of the trailer brake system. This makes it easy to achieve advantageous basic coordination between the braking systems of the towing vehicle and the trailer. However, this trailer control valve characteristic curve is no longer fixed and immutable for all operating situations. The invention advantageously utilizes the possibility of varying this trailer control valve characteristic curve as needed or replacing it with another characteristic curve.

[0017] According to one embodiment of the method according to the invention, it can be provided that the weight of the towing vehicle, the weight of the trailer vehicle, a coupling force between the towing vehicle and the trailer vehicle and / or a brake pressure or an angular position of a trailer axle that is actively or positively steered by a steering system of the trailer vehicle are detected, and that, depending on the detected value of at least one of these parameters, the trailer control valve characteristic curve for normal operation is varied, so that a special operation of the vehicle combination that is assessed as potentially inadmissible is preventively avoided or at least ended immediately after its detection.

[0018] To achieve harmonious braking coordination of a vehicle combination, for example, in an off-highway vehicle combination such as an agricultural tractor-trailer combination or a semi-trailer or bridge combination for special transport, the invention proposes determining the coupling force between the towing vehicle and the trailer and varying a trailer control valve characteristic curve depending on the coupling force. The coupling force can be measured at the coupling point between the towing vehicle and the trailer using a sensor, such as those used in power lifts for agricultural tractors.

[0019] The detected force can be a measure that influences the characteristic curve of the trailer control valve to be varied and ultimately used. In this case, a detected pushing force of the trailer would mean that the pressure in the trailer's pneumatic control line should be increased to a certain higher level in order to brake the trailer more strongly than before. A detected tractive force of the trailer would mean that the pressure in the trailer's pneumatic control line should be reduced to a certain lower level so that the trailer is braked less than before. The weight and weight distribution of the two vehicles in relation to each other can be used as an additional parameter. This method therefore makes it possible to react immediately to inadequate or uncomfortable braking coordination.The adjustment of the trailer control valve characteristic curve, depending on the coupling force between the vehicles, can ensure harmonious brake coordination and create greater safety against buckling of the vehicle combination.

[0020] Trailers for agricultural applications or for transporting heavy goods often have a pneumatic / hydraulic / mechanical steering system, for example, a positively steered trailing axle, which steers one or more axles of the trailer. In such a trailer, the pneumatic / hydraulic pressure of the steering system or the current angular position of a steered axle can be determined by the aforementioned electronic control unit. The current values ​​of these parameters can be used as an additional criterion for detecting a risk of the vehicle combination jackknifing when the towing vehicle brake system is not activated. In this case, using a suitable trailer control valve characteristic, the trailer can be temporarily braked for a few seconds to prevent the combination from jackknifing.

[0021] According to the invention, in a vehicle combination whose drive train has a hydrostatic continuously variable automatic transmission, a transmission output torque of the automatic transmission is continuously determined, that a special operation of the vehicle combination which deviates from normal operation is detected when the vehicle combination is braked in a driving state with the towing vehicle brake system not actuated due to a change in the gear ratio of the automatic transmission, as a result of which the trailer vehicle pushes itself onto the towing vehicle, and that in the case of this detected special operation, the trailer control valve characteristic curve for normal operation is replaced by a trailer control valve characteristic curve for this special operation, in which the trailer brake pressure is varied as a function of the determined transmission output torque of the automatic transmission.

[0022] In order to always achieve reliable braking of the trailer of a vehicle combination, the invention proposes controlling the trailer brake pressure via the trailer control valve as a function of the transmission output torque of the continuously variable automatic transmission in situations where the vehicle combination is decelerating and the braking system of the towing vehicle is not activated. The transmission output torque can be derived from existing data such as engine output torque, gear ratio, and efficiency of the hydrostatic automatic transmission and / or from the pressure in the hydraulic system of the automatic transmission.The relationship between negative transmission output torque, i.e., the braking torque in the driving situation, and trailer brake pressure can be derived from a trailer control valve characteristic curve that relates the tractor brake pressure to the trailer brake pressure, taking into account a further characteristic curve that relates the tractor brake pressure to a determined wheel brake torque of the towing vehicle. This achieves balanced braking characteristics or vehicle dynamics, regardless of whether the driver decelerates the vehicle combination with the service brake or a gear ratio change.

[0023] Furthermore, the invention provides that the trailer brake pressure is controlled as a function of the transmission output torque of the automatic transmission when the determined transmission output torque has exceeded a predetermined torque limit value in the direction of increasing vehicle deceleration.

[0024] To avoid the trailer brakes being applied too frequently, it is advantageous to apply trailer brake pressure to the trailer brakes only when a certain negative transmission output torque threshold has been exceeded.

[0025] According to a further embodiment of the invention, it can be provided that, in a vehicle combination whose drive train has an engine brake, an engine braking torque is continuously determined, that a special operation of the vehicle combination deviating from normal operation is detected if the vehicle combination is braked in a driving state with the towing vehicle brake system unactuated due to an engine braking torque, as a result of which the trailer vehicle pushes itself onto the towing vehicle, and that, in the event of this detected special operation, the trailer control valve characteristic curve for normal operation is replaced by a trailer control valve characteristic curve for this special operation, in which the trailer brake pressure is varied as a function of the detected engine braking torque. This ensures reliable braking of the trailer in the event of significant deceleration of the vehicle combination during driving operation due to the engine braking.

[0026] Another development of the method according to the invention provides that, for a vehicle combination whose drive train has a continuous braking torque, a continuous braking torque is continuously determined, that a special operation of the vehicle combination deviating from normal operation is detected if the vehicle combination is braked in a driving state with the towing vehicle brake system unactuated due to a continuous braking torque, as a result of which the trailer vehicle pushes onto the towing vehicle, and that, in the case of this detected special operation, the trailer control valve characteristic curve for normal operation is replaced by a trailer control valve characteristic curve for this special operation, in which the trailer brake pressure is varied as a function of the detected continuous braking torque. This ensures reliable braking of the trailer by the continuous braking brake in the event of significant deceleration of the vehicle combination during driving.

[0027] The described embodiments of the invention can also be combined with one another. For example, in a vehicle combination with a continuously variable automatic transmission, it is possible to measure both the transmission output torque of the transmission and the coupling force between the towing vehicle and the trailer vehicle, and to adapt a previously used trailer control valve characteristic curve accordingly or replace it with a suitable trailer control valve characteristic curve. The advantage of the method according to the invention is a balanced braking characteristic or vehicle dynamics, regardless of whether the driver decelerates the vehicle combination with the service brake or with the transmission, engine, or a continuous brake.

[0028] By way of example, a vehicle combination is described, such as an agricultural tractor-trailer combination, a semitrailer truck or a bridge combination, with an electronically controlled trailer control valve, with an electronic control device for controlling the trailer control valve, with an electronic memory for storing trailer control valve characteristics and with sensor means for detecting relevant parameters, such as a transmission output torque of a hydrostatic continuously variable automatic transmission, the weight of the towing vehicle and the trailer vehicle, a coupling force between the two vehicles and / or an angular position of a steered trailer axle, in which a method for braking control of the vehicle combination as described above and specified in the claims can be carried out.

[0029] The invention will be further explained below with reference to an embodiment shown in the accompanying drawing. Fig. 1 a schematic plan view of a vehicle train, Fig. 2 a trailer control valve characteristic curve for normal operation of a vehicle combination according to Fig. 1 , Fig. 3 a wheel brake torque characteristic of the towing vehicle according to Fig. 1 , and Fig. 4 a trailer control valve characteristic curve for a special operation of the vehicle combination according to Fig. 1 ,

[0030] The Fig. 1 shows, by way of example, a vehicle combination 1 known from DE 103 01 096 A1, on which the method according to the invention can be carried out. The vehicle combination 1 consists of a towing vehicle 2 to which a trailer vehicle 3 is coupled. The towing vehicle 2 has a towing vehicle braking system 4 for braking the towing vehicle 2. The trailer vehicle 3 has a trailer braking system 5 for braking the trailer vehicle 3. The two braking systems 4, 5 are actuated as part of a braking system with pressure medium such as compressed air or pressurized oil. The structure of such a braking system is described in the aforementioned DE 103 01 096 A1. The following description is limited to the components of the braking system relevant to the invention.

[0031] Accordingly, an electronic control device 6 is arranged in the towing vehicle 2, which serves to control various braking functions of the vehicle combination 1. The control device 6 is electrically connected to a front axle valve 7 of the towing vehicle braking system 4 for controlling the braking pressure in the wheel brakes 13a, 13b of the front wheels, and to a rear axle valve 8 of the towing vehicle braking system 4 for controlling the braking pressure in the wheel brakes 14a, 14b of the rear wheels of the towing vehicle 2. Furthermore, the electronic control device 6 is electrically connected to an electrically controllable trailer control valve 9 for controlling the braking pressure in the wheel brakes 15a, 15b, 16a, 16b of the trailer vehicle 3. The trailer control valve 9 is fluidly connected via a first brake line 10 to another valve designed as a trailer axle valve 11, which is not relevant here.The trailer axle valve 11 is hydraulically connected to the wheel brakes 15a, 15b, 16a, 16b of the trailer vehicle 3 via a second brake line 12. The brake lines 10, 12 for the wheel brakes 15a, 15b, 16a, 16b of the trailer vehicle 3 can be pressurized with brake pressure via the trailer control valve 9. The trailer brake pressure p_trailer can be controlled and varied, as explained below, using the control device 6 and the trailer control valve 9. According to the invention, the braking of the trailer vehicle 3 is controlled by a characteristic curve.

[0032] In addition, the vehicle train 1 has various sensors for vehicle dynamics control and for an anti-lock braking system, such as wheel speed sensors, steering angle sensors, lateral acceleration sensors and yaw rate sensors, as well as associated connecting lines that connect the said sensors to the electronic control device 6. These components are arranged in the vehicle train 1 according to Fig. 1 shown, but not provided with reference symbols and do not need to be explained further.

[0033] The Fig. 2 shows a trailer control valve characteristic curve p_normal for normal operation of the vehicle train 1 according to Fig. 1 . In this characteristic curve, the brake pressure p_tractor of the towing vehicle 2 is plotted against the brake pressure p_trailer of the trailer vehicle 3. The trailer control valve characteristic curve p_normal is approximately linear until a maximum system pressure is reached, which here is, for example, 10 pressure units. However, if the drive train of the vehicle combination 1 has a continuously variable automatic transmission, the vehicle combination can decelerate during driving operation due to a change in the gear ratio of the continuously variable automatic transmission and without actuating the service brake of the towing vehicle 2. The driver can, for example, influence and specifically use this option for vehicle braking using a control lever or by releasing the accelerator. In this case, the trailer control valve characteristic curve p_normal does not supply any trailer brake pressure p_trailer for normal operation, and the trailer vehicle 3 would collide with the towing vehicle 2 without braking.This situation is recognized by the control device 6 as a special operation.

[0034] Fig. 4 shows a new trailer control valve characteristic curve p_special for this special operation, which the control device 6 uses for the brake control of the trailer vehicle 3. In the diagram according to Fig. 4 the trailer control valve characteristic curve for the special operation p_special is shown, which indicates the dependence of the brake pressure p_trailer of the trailer vehicle 3 on the transmission output torque M_trans of the automatic transmission.

[0035] This trailer control valve characteristic curve p_special is derived from the Fig. 2 shown trailer control valve characteristic curve p_normal for normal operation and one in Fig. 3 The auxiliary characteristic curve p_aux shown, in which the towing vehicle brake pressure p_tractor is plotted against a wheel braking torque M_wheel brake of the towing vehicle 2, is derived. The wheel braking torque M_wheel brake of the towing vehicle 2 is measured during driving and is clearly correlated with the transmission output torque M_trans.

[0036] The control of the trailer brake pressure p_trailer is set according to the diagram in Fig. 4 It is only sensible to activate the brakes above a lower torque limit value M_lim, which results in a significant vehicle deceleration with the trailer 3 being pushed forward. With the aid of the trailer control valve characteristic curve p_special for special operation, the trailer 3 is reliably braked when the vehicle combination 1 decelerates due to a gear ratio change without the service brake being applied and the trailer control valve characteristic curve p_normal for normal operation is therefore not effective.

[0037] For the output torque of an engine brake or the output torque of a continuous brake of the towing vehicle 2, analog trailer control valve characteristics can be derived for a special operation and used to control the brakes of the trailer vehicle 3.

[0038] In a further embodiment, not explained in detail here, when a coupling force between the vehicles 2, 3 is detected, a similar trailer control valve characteristic curve can be derived and used to control the braking of the trailer vehicle 3. List of reference symbols (part of the description)

[0039] 1Vehicle combination 2Towing vehicle 3Trailer vehicle 4Towing vehicle brake system 5Trailer brake system 6Electronic control unit 7Front axle valve 8Rear axle valve 9Trailer control valve 10First brake line 11Trailer axle valve 12Second brake line 13a, 13bFront axle wheel brakes 14a, 14bRear axle wheel brakes 15a, 15bFirst trailer axle wheel brakes 16a, 16bSecond trailer axle wheel brakes M_limTorque limit value M_transTransmission output torque M_wheel brakeWheel brake torque p_auxAuxiliary characteristic curve p_normalTrailer control valve characteristic curve for normal operation p_specialTrailer control valve characteristic curve for special operation p_tractorTowing vehicle brake pressure p_trailerTrailer brake pressure

Claims

1. Method for brake control of a vehicle combination (1) consisting of a tractor vehicle (2) and a towed vehicle (3), wherein the tractor vehicle (2) has a pneumatic / hydraulic tractor vehicle brake system (4) and the towed vehicle (3) has a pneumatic / hydraulic trailer brake system (5), with an electrically controllable trailer control valve (9) which is assigned at least one trailer control valve characteristic curve (p_normal) which is stored in an electronic control device (6) for controlling a trailer brake pressure (p_trailer) of the trailer brake system (5) for normal operation of the vehicle combination (1), wherein, in the case of detection or prediction of special operation of the vehicle combination (1) which deviates from normal operation or is evaluated as potentially impermissible, the trailer control valve characteristic curve (p_normal) which is stored for normal operation of the vehicle combination (1) varies with consideration of parameters relevant to this situation or is replaced by a trailer control valve characteristic curve for special operation (p_special), wherein, in the case of the vehicle combination (1), the drive train of which has a hydrostatic continuously variable automatic transmission, a transmission output torque (M_trans) of the automatic transmission is continuously determined, wherein special operation, deviating from normal operation, of the vehicle combination (1) is detected when the vehicle combination (1) is braked in a travelling state with an unactuated tractor vehicle brake system (4) on the basis of a change in the transmission ratio of the automatic transmission, as a result of which the towed vehicle (3) pushes against the tractor vehicle (2), and wherein, for the case of this detected special operation, the trailer control valve characteristic curve for normal operation (p_normal) is replaced by a trailer control valve characteristic curve for this special operation (p_special), in which the trailer brake pressure (p_trailer) is varied as a function of the determined transmission output torque (M_trans) of the automatic transmission, characterized in that the trailer brake pressure (p_trailer) is controlled in a manner which is dependent on the transmission output torque (M_trans) of the automatic transmission if the determined transmission output torque (M_trans) has exceeded a predefined torque limit value (M_lim) in the direction of increasing vehicle retardation.

2. Method according to Claim 1, characterized in that the trailer control valve characteristic curve for normal operation (p_normal) of the vehicle combination (1) specifies the profile of a tractor vehicle brake pressure (p_tractor) of the tractor vehicle brake system (4) in relation to a trailer brake pressure (p_trailer) of the trailer brake system (5).

3. Method according to Claim 1 or 2, characterized in that the weight of the tractor vehicle (2), the weight of the towed vehicle (3), a coupling force between the tractor vehicle (2) and the towed vehicle (3) and / or a brake pressure or an angular position of a trailer axle which is steered in an active or forced manner by a steering system of the towed vehicle (3) are / is detected, and in that, in a manner which is dependent on the detected value of at least one of these parameters, the trailer control valve characteristic curve (p_normal) for normal operation is varied, with the result that special operation, evaluated as potentially impermissible, of the vehicle combination (1) is preventatively avoided or at least ended directly after it is detected.

4. Method according to one of Claims 1 to 3, characterized in that, in the case of a vehicle combination (1), the drive train of which has an engine brake, an engine braking torque is continuously determined, wherein special operation, deviating from normal operation, of the vehicle combination (1) is detected if the vehicle combination (1) is braked on account of an engine braking torque in a travelling state with an unactuated tractor vehicle brake system (4), as a result of which the towed vehicle (3) pushes against the tractor vehicle (2), wherein, for the case of this detected special operation, the trailer control valve characteristic curve for normal operation (p_normal) is replaced by a trailer control valve characteristic curve for this special operation (p_special), in which the trailer brake pressure (p_trailer) is varied as a function of the detected engine braking torque.

5. Method according to one of Claims 1 to 4, characterized in that, in the case of a vehicle combination (1), the drive train of which has a retarder brake, a retarder braking torque is detected continuously, wherein special operation, deviating from normal operation, of the vehicle combination (1) is detected if the vehicle combination (1) is braked on account of a retarder braking torque in a travelling state with an unactuated tractor vehicle brake system, as a result of which the towed vehicle (3) pushes against the tractor vehicle (2), wherein, for the case of this detected special operation, the trailer control valve characteristic curve for normal operation (p_normal) is replaced by a trailer control valve characteristic curve for this special operation (p_special), in which the trailer brake pressure (p_trailer) is varied as a function of the detected retarder braking torque.