Method for decelerating a vehicle combination

Abstract

The invention relates to a method for decelerating a vehicle combination having a towing vehicle and at least one trailer vehicle, wherein in the event that a requested deceleration is received, a brake control unit of the towing vehicle ascertains a total braking force (FBges) which is to be applied jointly by a trailer braking system (2) and a towing-vehicle braking system (1). The brake control unit causes the trailer braking system to apply a trailer braking force (FBA) and determines a towing-vehicle braking force (FBZ) taking account of the currently effective trailer braking force (FBA) and sets the towing-vehicle braking force (FBZ) by controlling the towing-vehicle braking sytem. The invention also relates to a brake control unit for the towing vehicle of a vehicle combination. In order to achieve the desired deceleration more quickly, the towing-vehicle braking force (FBZ) is, in a first braking phase (30) after receipt of the requested deceleration, initially set to a higher braking force level (FBZ1) than is intended according to the braking force distribution (28).

Description

[0001] Method for decelerating a vehicle combination

[0002] The invention relates according to claim 1 to a method for decelerating a vehicle combination comprising a towing vehicle and at least one trailer vehicle, wherein a brake control unit of the towing vehicle, upon receipt of a desired deceleration, determines a total braking force which is to be applied jointly by a trailer braking system and a towing vehicle braking system

[0003] In commercial vehicles, the wheels are usually braked using pneumatically actuated wheel brakes, with each vehicle in a vehicle combination having its own braking system. Electronic or automated braking systems are increasingly being used; instead of a mechanical connection between the brake pedal and the wheel brakes, the wheel brakes are actuated by electronic control of the wheel brake actuators. The brake pedal then acts as an operating device with which the driver communicates the desired deceleration. The detection of the desired deceleration using pedal travel sensors and transmission via electronic signal lines is also known as "brake by wire." In a vehicle combination, a brake control unit in the towing vehicle receives the desired deceleration and determines a braking force distribution of the partial braking forces to be applied by a towing vehicle braking system and a trailer braking system for the optimal implementation of the desired deceleration.The brake control unit of the towing vehicle then controls the towing vehicle brake system and also causes a trailer brake system to provide partial braking force for the trailer vehicle.

[0004] One advantage of electronically controlled deceleration (“brake by wire”) is the comparatively fast response of a vehicle’s wheel brakes.

[0005] DE44 38 353 C2 discloses a method for the electronic control or regulation of the braking system of a vehicle combination, wherein a towing vehicle that can be coupled to a trailer has an electronically controlled or regulated braking system. In the known method, a braking signal for the towing vehicle and a braking signal for the trailer are determined based on the driver's braking request to control its braking system. Depending on the design of the braking system, the known method uses various physical variables as the braking signal. The braking signal is transmitted pneumatically or electrically to the trailer. A pneumatic braking signal is the trailer braking pressure, which the brake control unit of the towing vehicle determines and provides to a coupling head for the trailer braking system. With electric brakes, the braking signal can be a target current supplied to the wheel brakes.

[0006] However, it has been found that the implementation of the desired deceleration in vehicle combinations is often not quick enough, especially in the case of pneumatic signal transmission between the towing vehicle and the trailer vehicle.

[0007] The present invention is based on the object of developing the generic method for decelerating a vehicle combination in such a way that the desired deceleration is achieved more quickly.

[0008] This object is achieved according to the invention by a method having the features of claim 1.

[0009] The invention is based on the realization that the advantages of electronic deceleration control ("brake by wire") can only be utilized to a limited extent in vehicle combinations if the trailer braking system of the coupled trailer is not electronically controlled and therefore the wheel brakes of the trailer respond significantly more slowly to the deceleration command. The invention provides that, in a first braking phase after receipt of the desired deceleration, the towing vehicle braking force is initially set to a higher braking force level than provided for by the brake force distribution. The brake control unit electrically controls the valves of the towing vehicle braking system to apply a greater braking force than is actually provided after the total braking force is divided between the partial braking forces of both braking systems.The quickly responding wheel brakes of the towing vehicle braking system can then cause a greater deceleration of the vehicle combination in the first braking phase, in which the trailer braking system does not yet participate in applying the total braking force (sum of the partial braking forces of both braking systems).

[0010] The temporary increase in partial braking force for the towing vehicle with an electronically controlled braking system can be easily achieved by the towing vehicle's brake control unit providing trailer brake pressure to the trailer braking system and adjusting it accordingly to the intended partial braking force for the trailer. The partial braking force of the rapid-response electronic braking system is set higher than the braking force level provided by the brake force distribution.

[0011] The reaction time of the vehicle combination to the requested deceleration is significantly reduced by the initially more intensive use of the towing vehicle braking system, especially in combination with conventional trailer braking systems. Furthermore, the braking distance of the vehicle combination is also shortened, ensuring the safe distance to a vehicle ahead is reliably maintained.

[0012] In the preferred embodiment of the invention, the towing vehicle brake system is controlled during the first braking phase to provide the total braking force in accordance with the desired deceleration. As a result, the requested desired deceleration is temporarily built up very quickly using only the rapidly responding wheel brakes of the electronically controlled towing vehicle brake system, as long as the comparatively slow-responding trailer brake system has not yet taken effect.

[0013] The first braking phase ends as soon as the trailer brake system begins to decelerate. The brake control unit 9 reduces the greater deceleration demand placed on the towing vehicle brake system as the deceleration process continues, so that the brake force distribution between the towing vehicle and the trailer is brought back into balance. In the preferred embodiment, the braking force of the towing vehicle brake system, which is initially greater in the first braking phase, is reduced in a transition phase after the trailer brake system begins to decelerate, taking the current trailer braking force into account, down to the intended level of the towing vehicle braking force. This ensures that an essentially constant total braking force of the braking systems of the vehicle combination is effective while the trailer braking force is building up.

[0014] The onset of the deceleration effect of the trailer brake system, i.e. an effect of braking forces from the trailer brake system on the deceleration of the vehicle combination, is determined or assumed in an advantageous embodiment of the invention. In a preferred embodiment of the invention, the onset of the deceleration effect of the trailer brake system is estimated by measuring the braking time as a forecast value based on an evaluation of the braking time with predetermined parameters. The braking time corresponds to the previous duration of the first braking phase with the towing vehicle braking force being controlled to a higher braking force level than intended according to the braking force distribution. The start of the measurement of the braking time can be linked to the time at which a trailer brake pressure is controlled or to the receipt of a desired deceleration. When a predetermined braking time is reached, a deceleration effect of the trailer brake system is assumed.

[0015] In a further embodiment of the invention, a predictive value is used to monitor the deceleration effect of the trailer brake system via a coupling force sensor. The coupling force sensor detects the forces between the towing vehicle and the towed trailer, with changes in the coupling force being used to draw conclusions about the deceleration effect of the trailer brake system. When a certain coupling force is detected, the onset of a deceleration effect of the trailer brake system is assumed.

[0016] In another embodiment, the predictive value for monitoring the deceleration effect of the trailer brake system is derived from an evaluation of the deceleration of the towing vehicle, which can be measured using an acceleration sensor. With knowledge of the currently effective towing vehicle braking force, conclusions can be drawn as to whether the measured deceleration of the towing vehicle must already have been achieved with the contribution of the trailer braking force, thus determining whether a deceleration effect of the trailer brake system can be determined.

[0017] In the case of semi-trailer trucks, the deceleration effect of the trailer braking system can be determined by evaluating the change in axle load on at least one axle. The axle load is measured as a predictor for monitoring the onset of the deceleration effect of the trailer braking system.

[0018] An embodiment of the invention is explained in more detail below with reference to the drawings. They show:

[0019] Fig. 1 is a pneumatic and electrical diagram of an embodiment of a combination of braking systems of a vehicle combination,

[0020] Fig. 2 is a flow chart of an embodiment of a method for decelerating the vehicle combination according to Fig. 1,

[0021] Fig. 3 is a graphical representation of a temporal progression of the partial braking forces during deceleration.

[0022] Fig. 1 shows an electro-pneumatic plan of a combination of pneumatic braking systems 1, 2 of the commercial vehicles 3, 4 of a vehicle combination 5, namely a towing vehicle 3 with, in the exemplary embodiment, a trailer vehicle 4. Electrical lines are shown with solid lines and pneumatic lines with dotted lines. To brake the wheels 6, each wheel 6 is assigned a wheel brake 7 which can be actuated pneumatically via brake cylinders 8. The wheel brakes 7 exert a braking force on the rotating wheel 6 in accordance with the pneumatic brake pressure present in the brake cylinder 8 in order to decelerate the vehicle combination 5. A brake pressure P acts on the wheel brakes 7 of the towing vehicle braking system 1, which brake pressure is electronically controlled by a brake control unit 9. In the trailer braking system 2, a trailer brake pressure PA acts which, in the exemplary embodiment shown, is provided and adjusted by the brake control unit 9 of the towing vehicle 3.

[0023] A brake pedal 10 is arranged in the driver's cab of the towing vehicle 3, the position of which is detected by a brake signal transmitter 11 connected to the brake control unit 9. The driver of the towing vehicle 3 can specify a desired deceleration z-target by actuating the brake pedal 10 of the brake control unit 9. In the exemplary embodiment shown, the wheel brakes 7 of the front axle 12 of the towing vehicle are assigned to a common first brake circuit 13 of the electronically controlled towing vehicle brake system 1, while the wheel brakes 7 of the rear axle 14 can be actuated via a second brake circuit 15. A first pressure fluid reservoir 16 is assigned to the first brake circuit 13, and a second brake circuit 15 of the rear axle 14 is supplied with pressure fluid via a second pressure fluid reservoir 17.

[0024] The towing vehicle brake system 1 comprises a pneumatic coupling head 18 to which the trailer brake system 2 of the trailer vehicle 4 can be coupled. Via the coupling head 18, the towing vehicle brake system 1 provides a pneumatic trailer brake pressure P-A for the trailer brake system 2. A trailer control valve 19 is assigned to the coupling head 18, which controls the connection between a third pressure reservoir 20 and the pneumatic coupling head 18. The trailer brake system 1 has a trailer brake circuit 21 in which the trailer brake pressure PA provided by the towing vehicle 1 prevails and can be switched through to all wheel brakes 7. By setting and providing the trailer brake pressure PA, the brake control unit 9 of the towing vehicle brake system 1 causes the trailer brake system 2 to provide a trailer braking force.

[0025] Each brake cylinder 8 is preceded by an electrically controllable pressure control valve 22. To receive control signals, the pressure control valves 22 of the towing vehicle brake system 1 are connected to the brake control unit 9, which influences the brake pressure P through corresponding control signals. The rotational behavior of the wheels 6 is also monitored. Each wheel 6 is assigned a speed sensor 24, which generates measurement signals indicating the rotational behavior of the respective wheel 6. From the measurement signals of the speed sensors 24, the brake control unit 9 determines information about the slip of the respective wheel 6.

[0026] The trailer vehicle 4 has an anti-lock braking system with brake electronics 23, which are designed to control the pressure control valves 22 on the brake cylinders of the trailer brake system 2 and to intervene if the wheels tend to lock during braking under the influence of the trailer brake pressure PA. The brake electronics 23 monitors the slip of the individual wheels, which occurs when the brakes are applied, via the speed sensors 24. The braking force to be applied is determined pneumatically by the brake control unit 9 of the towing vehicle via the readily available trailer brake pressure PA. If a tendency to lock of an individual wheel is detected, the brake electronics 23 counteracts the locking of the affected wheels by controlling one or more pressure control valves 22 and regulating the brake pressure along the slip limit.

[0027] Fig. 2 illustrates in a flowchart an embodiment of the method for decelerating the vehicle combination 5 after the driver specifies a desired deceleration z-setpoint to the brake control unit by actuating the brake pedal and the brake signal transmitter 11 coupled to the brake pedal. After determining 27 a total braking force FBges for implementing the desired deceleration z-setpoint, the brake control unit determines a braking force distribution 28 for this total braking force FBges, i.e. the braking force level of the towing vehicle braking force FBZ, which is to be applied by the towing vehicle braking system 1 as part of the total braking force FBges, and the braking force level of the trailer braking force FBA, which is to be applied by the trailer vehicle. In accordance with the intended partial braking force FBA for the trailer vehicle, the brake control unit provides a trailer braking pressure and thus causes the trailer braking system 2 to implement the trailer braking force FBA.Taking into account the trailer braking force FBA, the setting 29 of the towing vehicle braking force FBZ is made, which ultimately should reach the braking force level FBZ2 according to the braking force distribution 28. The brake control unit controls the wheel brakes of the towing vehicle braking system 1 accordingly.

[0028] The electronically controlled towing vehicle brake system responds more quickly than the trailer brake system which is pneumatically activated by the brake control unit 9 of the towing vehicle via the trailer brake pressure PA. A temporal progression of the partial braking forces FBZ, FBA is shown in Fig. 3. While the electronically controlled towing vehicle brake system 1 begins to build up the towing vehicle braking force FBZ at time t1, the braking response of the trailer brake system 2 occurs at time t2. Only from time t3 does the effective trailer braking force FBA of the trailer brake system reach the braking force level FBA1 which is determined according to the requested braking force distribution 28 (Fig. 2). In order to implement the desired deceleration z-target as quickly as possible, the brake control unit initially sets the towing vehicle braking force in a first braking phase 30 immediately after receiving the desired deceleration z-target to a higher braking force level FBZ1 than that provided for by the braking force distribution 28.Accordingly, the brake control unit controls the towing vehicle brake system to apply a greater braking force than the partial braking force provided by the brake force distribution 28. In the illustrated embodiment, the towing vehicle braking force FBZ is set to an increased braking force level FBZ1 during the first braking phase 30, which corresponds to the requested total braking force FBges.

[0029] The first braking phase 30 ends as soon as a deceleration effect of the trailer braking system occurs or is assumed. It lasts in the graphical progression of the partial braking forces according to Fig. 3 until the active effect of the trailer braking system 2 occurs or is assumed at time t2.

[0030] The brake control unit 9 is designed to monitor, at the start of the deceleration process, whether the trailer brake system 2, with its slower braking response, has already become effective and is actively contributing to the deceleration of the vehicle combination 5. During the first braking phase 30, a deceleration effect 31 of the trailer brake system 2 is monitored 26, and the first braking phase 30 is terminated as soon as a deceleration effect 31 occurs or can be assumed.

[0031] After determining or assuming a deceleration effect 31 of the trailer brake system at time t2, the initially greater towing vehicle braking force FBZ of the towing vehicle braking system 1, starting from the higher braking force level FBZ1, which corresponds to the total braking force FBges, is reduced in a transition phase 32 until time t3, at which the trailer braking force FBA reaches the intended braking force level FBA1, taking into account the current trailer braking force FBA, to the intended braking force level FBZ2.Already during transition phase 32, at the same time as the partial braking force of the trailer braking system is continuously increased due to the acting trailer braking pressure up to the intended braking force level FBA1, the electrical braking request to the electronically controlled towing vehicle braking system is reciprocally reduced, so that the desired total braking force FBges is always achieved in the sum of both partial braking forces, i.e. the sum of towing vehicle braking force FBZ and trailer braking force FBA.

[0032] The occurrence of a deceleration effect 31 is determined or assumed based on the evaluation of a measured forecast variable 33. Determination of the deceleration effect 31 is possible if a variable is measured and evaluated as the forecast variable 33 which changes with the onset of the deceleration effect of the trailer braking system. This can be the evaluation of a coupling force as a forecast variable, which is recorded by a coupling force sensor. Another option for obtaining the desired information about the onset of the deceleration effect and thus the end of the first braking phase is the evaluation of a measured deceleration of the towing vehicle as a forecast variable. In the case of semi-trailer trucks, the change in the axle load on one or more axles can be measured as a forecast variable containing information about the onset of the deceleration effect.

[0033] In the illustrated embodiment, monitoring 26 of the deceleration effect 31 of the trailer brake system is carried out indirectly by evaluating a braking time t as a forecast variable 33. Upon reaching a specific braking time t2, a deceleration effect of the trailer brake system is assumed. The braking time t2, upon reaching which the trailer braking force FBA is assumed to become effective, is a specification 25, with the parameters for determining the specification being determined empirically. In the illustrated embodiment, the brake control unit of the electronic braking system links the start of the measurement of the braking time t2 to the pneumatic activation of the trailer braking force FBA by providing the trailer brake pressure.

[0034] List of reference symbols (part of the description) Towing vehicle brake system Trailer brake system Towing vehicle Trailer vehicle Vehicle combination Wheel Wheel brake Brake cylinder Brake control unit Brake pedal Brake signal generator Front axle First brake circuit Rear axle Second brake circuit First pressure medium reservoir Second pressure medium reservoir Coupling head Trailer control valve Third pressure medium reservoir Trailer brake circuit Pressure control valve Brake electronics Speed ​​sensor Specifications Monitoring Determination Total deceleration Brake force distribution Adjustment Brake force First braking phase Effectiveness Transition phase Forecast variable io P Brake pressure

[0035] PA Trailer brake pressure z-target Desired deceleration t Braking time t1 Time t2 Time t3 Time

[0036] FBZ towing vehicle braking force

[0037] FBA trailer braking force

[0038] FBZ1 higher braking force level

[0039] FBZ2 brake force level according to brake force distribution

[0040] FBA1 braking force level

[0041] FBges total braking force

Claims

Claims 1. Method for decelerating a vehicle combination (5) with a towing vehicle (3) and at least one trailer vehicle (4), wherein a brake control unit (9) of the towing vehicle (3), upon receipt of a desired deceleration (z-soll), determines a total braking force (FBges) which is to be applied jointly by a trailer braking system (2) and a towing vehicle braking system (1) in a braking force distribution (28), wherein the brake control unit (9) causes the trailer braking system (2) to apply a trailer braking force (FBA) and determines a towing vehicle braking force (FBZ) taking into account the currently effective trailer braking force (FBA) and sets it by controlling the towing vehicle braking system (1), characterized in that the towing vehicle braking force (FBZ) is initially set to a higher braking force level (FBZ1) than is provided for according to the braking force distribution (28) in a first braking phase (30) after receipt of the desired deceleration (z-soll).

2. Method according to claim 1, characterized in that the towing vehicle braking force (FBZ) is set to a braking force level (FBZ1) corresponding to the total braking force (FBges) during the first braking phase (30) and the towing vehicle braking system (1) is controlled accordingly.

3. Method according to claim 1 or 2, characterized in that during the first braking phase (30) a deceleration effect (31) of the trailer brake system (2) is monitored (26) and the first braking phase (30) is ended as soon as a deceleration effect (31) occurs or is assumed.

4. Method according to claim 3, characterized in that the monitoring (26) of the deceleration effect (31) of the trailer brake system (2) is carried out indirectly via a measured forecast variable (33).

5. Method according to one of the preceding claims, characterized in that after determining or assuming a deceleration effect (31) of the trailer brake system (2), the initially greater towing vehicle braking force (FBZ) of the The towing vehicle braking system (1) is reduced in a transition phase (32) taking into account the currently effective trailer braking force (FBA) to the braking force level (FBZ2) of the towing vehicle braking force (FBZ) provided according to the braking force distribution (28).

6. Brake control unit (9) for the towing vehicle (3) of a vehicle combination (5) with a towing vehicle (3) and at least one trailer vehicle (4), wherein the brake control unit (9) is designed to determine, upon receipt of a desired deceleration (z-target), a total braking force (FBges) which is to be applied jointly by a trailer braking system (2) and a towing vehicle braking system (1) in a braking force distribution (28), and wherein the brake control unit (9) is designed to cause the trailer braking system (2) to apply a trailer braking force (FBA) and to determine a towing vehicle braking force (FBZ) taking into account the currently effective trailer braking force (FBA) and to set it by controlling the towing vehicle braking system (1), characterized in that the brake control unit (9) is designed toto initially set the towing vehicle braking force (FBZ) in a first braking phase (30) after receiving the desired deceleration (z-target) to a higher braking force level (FBZ1) than provided for by the braking force distribution (28).

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