Method for controlling the drive of a trailer and drive device

Abstract

Method for controlling the drive of a trailer (1), wherein the trailer (1) has at least one electric machine (3, 4) for driving at least one axle (10) of the trailer (1), wherein the trailer (1) comprises a force sensor (5) for detecting measured tractive force values ​​(102) that occur between a towing vehicle (2) and the trailer (1) coupled thereto, wherein a desired tractive force value (104) is determined as a function of at least one measured tractive force value (102), a selected direction of travel, and a braking request, and wherein a desired torque value (107a, 107b) is set on the at least one electric machine (3, 4) as a function of the desired tractive force value (104), characterized in that measured tractive force values ​​(102) detected by the force sensor (5) are combined with a reference variable (101) in a control loop in order to determine a desired tractive force value (104) therefrom.that the reference variable (101) is calculated as a function of the selected direction of travel and as a function of the braking request, and that the reference variable (101) is determined as a function of the state of charge of a battery (11) of the trailer (1).

Description

[0001] The present invention relates to a method for controlling the drive of a trailer with an electric motor drive. Furthermore, a drive device and a computer program product are proposed that are intended for implementing the method.

[0002] DE 11 2018 005 128 T5 discloses a system and method for a trailer towed by a vehicle. The trailer comprises an axle with wheels that can be driven by an electric motor or by two electric motors. The trailer comprises an electronic control unit configured to control the electric motors. The electronic control unit, in turn, comprises a receiver that receives electronic signals from components of the trailer and the vehicle. Using the received signals, a drive force required at each wheel to assist the vehicle in driving the vehicle combination is calculated.

[0003] Furthermore, DE 41 33 912 A1 discloses a vehicle combination comprising a towing vehicle and a trailer attached to it via a drawbar, wherein the drive wheels of one axle of the trailer are driven by electric motors. An electronic control system is provided to supply the aforementioned electric motors of the trailer with controlled electrical power, with the drive force of the electric motors being dimensioned such that a minimum tractive force on the drawbar is not exceeded during forward travel. The tractive force on the drawbar is determined by a sensor. The electronic control system determines the speed of the electric motors depending on the steering angle and the speed of the towing vehicle.

[0004] DE 10 2019 130 859 A1 discloses an electric drive and braking system for a trailer that can be coupled to a towing vehicle and is capable of overrun braking. The parameters required to control the electric drive and braking system are recorded by a recording device and / or a detection device, each of which is arranged on the trailer.

[0005] Furthermore, DE 10 2019 202 784 A1 discloses a trailer for a vehicle in which the two wheels of an axle can each be driven by an electric motor. The trailer further comprises a control device, a measuring device for determining a force between the trailer and the vehicle, and a detection device for determining the vehicle's drive type. The two electric motors are to be individually controlled so that a defined force acts on the vehicle.

[0006] DE 10 2018 005 122 T5 discloses a system and method for a trailer towed by a vehicle. The trailer comprises an axle with two wheels and at least one electric motor coupled thereto, as well as a coupling force sensor that measures a coupling force exerted by the vehicle on the trailer. The system comprises receiving means for receiving a vehicle braking signal from a subsystem of the vehicle. The system further comprises processing means that determine a wheel braking force based on signals from both systems of the towing vehicle and from the coupling force sensor. Finally, control means are provided that cause the at least one electric motor to exert a force on the wheel to which it is coupled, depending on the determined value of the wheel braking force of the trailer.

[0007] US 2021 / 0 291 667 A1 discloses a trailer comprising a battery and an axle or tandem axle with wheels driven by electric motors. The battery is designed to supply power to the electric motors when the trailer is towed on public roads. The trailer further comprises sensor means that detect forces on a trailer coupling in at least one longitudinal and / or transverse direction of the trailer and / or the vertical direction, as well as a controller that controls the electric motors so that a minimum and / or maximum limit is maintained.

[0008] Finally, a method is known from DE 10 2017 110 520 A1 which comprises the following steps: Direct or indirect measurement of at least one force acting on a trailer; Determination of a driving state of the trailer depending on the measured force; Controlling an electric motor coupled to a wheel of the trailer such that, depending on the determined driving state, the electric motor is operated in motor mode, in generator mode, or in idle mode. Furthermore, DE 10 2017 110 520 A1 describes a trailer with a sensor designed to measure a force acting on the trailer, with an electric motor coupled to at least one wheel of the trailer. A control unit of the trailer is designed to control the electric motor based on data determined by the at least one sensor and depending on a determined driving state, to operate the electric motor in motor mode, in generator mode, or in idle mode.

[0009] Furthermore, the article "FREIMANN, Rüdiger [et al.]: Central electric drive for lightweight caravans. In: Automobiltechnische Zeitschrift, Vol. 121, 2019, No. 10, pp. 60-65. - ISSN 0001-2785" discloses a method for controlling the drive of a caravan. The caravan has at least one electric motor for driving an axle, and the caravan includes a force sensor for recording tractive force measurements that occur between a towing vehicle and the coupled caravan and are used to control the electric motor.

[0010] The object of the present invention is to provide a method for controlling the drive of a trailer with an electric motor drive and a corresponding drive device that ensures simple and advantageous operation with regard to energy efficiency and safety. Furthermore, a corresponding computer program product is to be specified.

[0011] These objects are achieved by a method having the features of claim 1, by a drive device according to claim 8, and by a computer program product according to claim 9. Advantageous embodiments are specified in the dependent claims.

[0012] A method is specified for controlling the drive of a trailer, wherein the trailer has at least one electric machine for driving at least one axle of the trailer. For example, two wheels of an axle of the trailer can be driven by an electric motor via a transfer case. In other embodiments, each individual wheel of an axle of the trailer can be driven by an associated electric motor. The aforementioned electric motors can each be operated as a motor or as a generator. With the aid of the generator operation of the electric motors, a braking process can be assisted and, at the same time, an electrical energy storage device, i.e., a battery, can be charged.

[0013] The trailer further comprises a force sensor for detecting a tractive force between a towing vehicle and the trailer coupled to it. The force sensor thus detects measured tractive force values. A target tractive force value is then determined depending on at least one measured tractive force value, a selected direction of travel, and a braking request. A target torque value is set on the at least one electric motor depending on the target tractive force value. The target torque value is dimensioned such that a desired tractive force is established or maintained between the towing vehicle and the trailer. The target torque value can, for example, correspond to a specific input current with which the electric motor is operated to achieve the required torque.

[0014] The measured tractive force values ​​recorded by the force sensor are combined with a reference variable in a control loop to determine a tractive force setpoint. The reference variable is calculated depending on the selected direction of travel and the braking requirement. The torque output by the electric motor is then set depending on the tractive force setpoint. This means that the tractive force setpoint is used as the reference variable for controlling the electric motor. The torque therefore drives the trailer's drive wheels, thus supporting the drive of the entire vehicle combination. In versions with multiple electric motors to drive the trailer's drive wheels, a corresponding torque can be set on each individual electric motor depending on the tractive force setpoint.

[0015] To implement the method, a closed control loop can be provided in which the measured tractive force values ​​are fed back and summed with the determined reference variable. A feedback controller determines the tractive force setpoint from this. In addition, further parameters can be taken into account in a feedforward control and fed into the control loop. From the tractive force setpoint, a required torque is then determined with which the drive wheels on the trailer axle are to be driven in order to achieve the desired tractive force. Using the tractive force setpoint, a desired actual value of the tractive force can be controlled, which at least lies within a predetermined range. PID control is particularly suitable for this purpose. The system can therefore be controlled such that a target tractive force is achieved in a steady state, i.e. at a constant speed. The proposed method can also minimize the energy consumption of the towing vehicle.

[0016] To ensure optimal handling of the entire vehicle combination, i.e., the towing vehicle and trailer, the target tractive force can be determined in such a way that a minimum tractive force is not undercut during driving. Maintaining a constant tractive force between the towing vehicle and the trailer can achieve high driving stability.

[0017] The selected direction of travel and the braking request can advantageously be determined from the value of a signal transmitted via a connector between the towing vehicle and the trailer. A signal for the selected direction of travel and a braking request are already transmitted in conventional trailer connectors to control the trailer's electrical lighting accordingly. This controls the brake lights and a reversing light on the trailer.

[0018] In a simple embodiment of the invention, no additional sensors or other effort are required to control and regulate the trailer drive other than the force sensor. It is particularly advantageous if the connector plug is designed according to the ISO 11446 standard. In many countries, such 13-pin connectors are the most commonly used and commercially available connector plugs for car trailers. Using the proposed method, the drive of an electrically driven trailer can be controlled autonomously and independently of the respective towing vehicle. The towing vehicle does not require any additional equipment to use the method according to the invention. A conventional trailer coupling with a conventional connection socket is sufficient. This results in extremely simple and broad applicability for the advantageous use of such a trailer.The proposed method is therefore designed in such a way that it requires minimal information from the towing vehicle, in particular only the information transmitted via a connector according to the aforementioned standard.

[0019] According to the invention, the reference variable is determined depending on the charge level of the trailer's battery. This allows the trailer's electric motor to provide a relatively high level of drive assistance at a high charge level, while the drive assistance is regulated to a correspondingly lower level at a low charge level.

[0020] Furthermore, a driving resistance value can be taken into account to determine the target tractive force value. The driving resistance value includes at least one of the following: rolling resistance value, air resistance value, gradient resistance value, and acceleration resistance value. The greatest advantage is achieved when each of these resistance values ​​is taken into account and the corresponding resistances are compensated by adjusting the drive power of at least one electric motor. This can improve the overall efficiency of the vehicle combination and achieve comfortable driving behavior.

[0021] The driving resistance value can be determined at least partially using speed signals from at least one speed sensor located on the trailer. A rolling resistance value and an air resistance value can be determined from a speed and a derived driving speed. The acceleration resistance value can also be determined from the speeds or their change over time. A standard speed sensor of the electric motor can be used as a speed sensor, for example.

[0022] In one embodiment of the invention, the trailer may also comprise an inclination sensor, for example in the form of an inertial measuring unit (IMU), to determine a gradient resistance value.

[0023] In a further embodiment, a brake sensor can also be provided on an overrun brake of the trailer. Using the brake sensor on the overrun brake, a braking status or a braking force value can be recorded and used to determine the target tractive force. Such an additional brake sensor serves to improve safety. For example, the above-mentioned braking request can be confirmed by the connecting plug using a signal representing the level of braking pressure on the overrun brake. In a simpler embodiment, the signal can simply indicate the braking status, i.e., whether the brake is currently applied or not. A typical overrun brake is only applied once the vehicle combination has decelerated to a certain level, so the overrun brake is not applied during light and moderate braking.It can be a significant safety advantage if information about the status of the overrun brake is taken into account when determining the target tractive force. Together with the signal for the above-mentioned braking request, which is transmitted via the connecting plug, the signal for the status or brake pressure of the overrun brake creates redundancy that contributes to increased safety. This means that even if the connecting plug is defective, braking by the towing vehicle can be detected via the signal from the overrun brake. In this case, too, a negative torque can be set on the electric machine, whereby the electric machine also has a decelerating, i.e. brake-enhancing effect. This can shorten the braking distance of the vehicle combination in critical situations. While the electric machine supports braking processes, it can be operated as a generator.This allows electrical energy to be fed back into the battery, which in turn increases the overall efficiency of the drive system.

[0024] Even with the version with a brake sensor on the overrun brake, the trailer's drive can be controlled independently and independently of the towing vehicle. Therefore, a towing vehicle with a conventional trailer coupling and a conventional connection socket is sufficient, allowing the trailer to be operated with any conventional towing vehicle.

[0025] To improve cornering performance, it can further be provided that a cornering radius is determined using angle signals from an angle sensor mounted on the trailer, and that two drive wheels on the trailer axle are driven with different torques, which are calculated depending on the determined cornering radius. In this way, the agility and maneuverability of the vehicle combination can be improved, in particular.

[0026] Finally, the present invention also relates to a drive device for a trailer. The drive device comprises at least one electric machine for driving at least one axle of the trailer. The drive device further comprises a force sensor for detecting a tractive force between the towing vehicle and the trailer coupled thereto. A control unit is provided for controlling the at least one electric machine. This control unit is configured to control a method as described above. In further embodiments, the drive device can comprise additional components and in particular sensors that are mentioned in the above description and are required for carrying out the various embodiments of the method.

[0027] Finally, a computer program product is also proposed. The computer program product comprises instructions that, when executed on a computer, cause the method described above to be carried out.

[0028] In the following, the invention and its advantages are explained in more detail with reference to the embodiment shown in the attached figures.

[0029] Showing: Fig. 1 a schematic representation of a vehicle combination with a towing vehicle and an electrically driven trailer and Fig. 2 a control circuit for the drive control of a trailer.

[0030] The Fig. The towing vehicle 2 shown in Figure 1 and the trailer 1 coupled to it together form a vehicle combination. The mechanical coupling of the trailer 1 to the towing vehicle 2 takes place via a conventional trailer coupling 8, which is arranged on a drawbar 9 of the trailer 1. Furthermore, the towing vehicle 2 is connected to the trailer 1 via an electrical connection. For this purpose, the towing vehicle 2 has a socket 7, which is coupled to a 13-pin connecting plug 6 of the trailer 1. This conventional electrical connection serves primarily to supply the electrical lighting system of the trailer 1. Within the scope of the present invention, however, the signals transmitted via this electrical connection are also used to control the drive device of the trailer 1.

[0031] A force sensor 5 for detecting the tractive force between the towing vehicle 2 and the trailer 1 coupled to it is arranged on the trailer coupling 8. The force sensor 5 is connected to a control unit 12 via a data transmission link. The measured tractive force values ​​102 detected by the force sensor 5 thus represent the actual value of the tractive force. The measured tractive force values ​​102 are used in the control unit 12 to determine a target tractive force value 104 by feeding them back into a control loop and combining them with a determined reference variable.

[0032] The trailer 1 is equipped with two electric motors 3, 4, which are intended to drive the drive wheels 13 and 14 on an axle 10 of the trailer 1. The two electric motors 3, 4 are controlled by a control unit 12 via an inverter 15, 16, respectively. To control the two electric motors 3, 4, the determined tractive force setpoint 104 is activated so that they drive the respective associated drive wheel 13 or 14 with a specific torque. The electric motors 3, 4 are controlled in such a way that a minimum tractive force is not undercut.

[0033] A battery 11 is provided to supply power to the electrical machines 3, 4. The battery 11 is connected to the electrical machines 3, 4 via the inverters 15, 16. To drive the electrical machines 3, 4 and thus to drive the trailer 1, electrical current is fed from the battery 11 to the electrical machines 3, 4. During generator operation of the electrical machines 3, 4, electrical energy is fed back into the battery 11, thus charging the battery 11.

[0034] Furthermore, the battery 11 is connected to the control unit 12 via a data transmission connection, whereby data on the charge state of the battery 11 is transmitted to the control unit 12.

[0035] In the area of ​​the drawbar 9 there is also an overrun brake 18. If initially only the towing vehicle 2 is braked, the trailer 1 runs into the towing vehicle 2. This force is transferred from the trailer coupling 8 to the brakes of the trailer 1, for example via mechanical levers. Pressure-medium actuated overrun brakes are also possible. The braking force exerted by the overrun brake 18 depends on how strongly the towing vehicle 2 decelerates and on the mass of the trailer 1. Compared to an unbraked trailer, the pushing effect is less, thus increasing driving stability during braking maneuvers. A brake sensor 17 is arranged on the overrun brake 18 and records a braking status and / or a braking force value of the overrun brake 18. The braking status or braking force value is transmitted to the control unit 12 via a data transmission connection. The braking status or braking force value is stored in the control unit 12.the braking force value is used to determine the traction force target value 104.

[0036] In the present embodiment, the trailer 1 also has an inertial measuring unit 19, which can, among other things, fulfill the function of an inclination sensor.

[0037] Using this inertial measuring unit 19, for example, a road gradient can be determined, which in turn can be used to determine a gradient resistance value. The gradient resistance value can be used within the framework of the proposed method for calculating a general driving resistance value 106 to determine the tractive force target value 104. The inertial measuring unit 19 is also connected to the control unit 12 via a data transmission connection. These data transmission connections can be implemented either as a cable connection or wirelessly using radio technology.

[0038] The control unit 12 comprises at least one processor and at least one data memory coupled to the processor. Furthermore, the control unit 12 comprises suitable interfaces for communication with other components of the trailer 1. This is, for example, an input interface for the measured tensile force values ​​102 of the force sensor 5 and a further input interface for signals transmitted via the connecting plug 6. A program code is stored in the data memory, which can be executed by the processor so that the steps of the proposed method are carried out. In addition, data can be stored in the data memory that is used to determine the reference variable and / or the nominal tensile force value 104. The control unit 12 can further comprise power electronics coupled to the processor for controlling the two electrical machines 3, 4 and their inverters 15, 16.

[0039] In the Fig. Figure 2 shows a control loop 100 for controlling the drive of trailer 1. In the control loop 100, a reference variable 101 is determined taking into account various parameters 101a, 101b, and 101c. In this case, the following parameters are used to calculate the reference variable 101: • Battery charge level101a, • Status of a brake request 101 b and • the selected direction of travel 101c, ie forward or reverse travel, is used to determine the reference variable 101.

[0040] The reference variable 101 is combined with the controlled variable, namely the measured tractive force value 102, and compared. The returned measured tractive force values ​​102 can pass through a low-pass filter 109, which filters out interfering, high-frequency components of the signal. Using a feedback controller 103 and taking into account a driving resistance value 106, a tractive force setpoint 104 is determined from this as a manipulated variable. In the further control system 105, the determined tractive force setpoint 104 is converted into corresponding torque setpoints 107a, 107b, on the basis of which the two electric motors 3, 4 and the respective drive wheel 13, 14 of the trailer 1 are driven with a desired torque.

[0041] Additionally, curve radius values ​​108 can be taken into account when calculating the torque setpoints 107a, 107b, allowing the trailer 1 to be driven in curves with different torque setpoints 107a and 107b. In this way, a desired curve path of the trailer 1 and high driving stability can be achieved. The curve radius values ​​108 are recorded using the angle signals of an angle sensor 20 arranged on the drawbar 9 of the trailer 1. Reference symbol 1 trailer 2 towing vehicle 3 electric machine 4 electric machine 5 force sensor 6 connecting plugs 7 socket 8 trailer coupling 9 Drawbar 10 axis 11 Battery 12 Control unit 13 Drive wheel 14 Drive wheel 15 inverters 16 inverters 17 Brake sensor 18 Overrun brake 19 inertial measuring unit 20 angle sensor 100 control loop 101 Management variable 102 Tensile force measurement 103 feedback controllers 104 Traction force setpoint 105 Control system 106 Driving resistance value 107a Torque setpoint 107b Torque setpoint 108 Curve radius value 109 Low pass

Claims

[1] Method for controlling the drive of a trailer (1), wherein the trailer (1) has at least one electric machine (3, 4) for driving at least one axle (10) of the trailer (1), wherein the trailer (1) comprises a force sensor (5) for detecting measured tractive force values ​​(102) that occur between a towing vehicle (2) and the trailer (1) coupled thereto, wherein a desired tractive force value (104) is determined as a function of at least one measured tractive force value (102), a selected direction of travel and a braking request, and wherein a desired torque value (107a, 107b) is set on the at least one electric machine (3, 4) as a function of the desired tractive force value (104), characterized bythat measured tractive force values ​​(102) detected by the force sensor (5) are combined in a control loop with a reference variable (101) in order to determine a reference force setpoint (104) therefrom, that the reference variable (101) is calculated as a function of the selected direction of travel and as a function of the braking requirement, and that the reference variable (101) is determined as a function of the state of charge of a battery (11) of the trailer (1). [2] Method according to claim 1, characterized by that the selected direction of travel and the braking request are each determined from the value of a signal which is transmitted via a connecting plug (6) between the towing vehicle (2) and the trailer (1). [3] Method according to claim 2, characterized by that the connecting plug (6) is designed according to the ISO 11446 standard. [4] Method according to one of the preceding claims, characterized byin that a driving resistance value (106) is taken into account to determine the desired tractive force value (104), wherein the driving resistance value (106) comprises at least one of the rolling resistance value, air resistance value, gradient resistance value and acceleration resistance value. [5] Method according to claim 4, characterized by that the driving resistance value (106) is determined with the aid of speed signals from at least one speed sensor arranged on the trailer (1). [6] Method according to one of the preceding claims, characterized by that a braking status or a braking force value is detected by means of a braking sensor (17) on an overrun brake (18) of the trailer (1) and is used to determine the desired tractive force value (104). [7] Method according to one of the preceding claims, characterized by that the tractive force setpoint (104) is determined in such a way that a minimum tractive force is not undercut during driving operation. [8] Drive device for a trailer (1), with at least one electric machine (3, 4) for driving at least one axle (10) of the trailer (1), with a force sensor (5) for detecting a tractive force between a towing vehicle (2) and the trailer (1) coupled thereto, and with a control unit (12) for controlling the drive of the at least one electric machine (3, 4), characterized by that the control unit (12) is designed to control a method according to one of the preceding claims. [9] Computer program product comprising instructions which cause the control unit (12) of the drive device according to claim 8 to carry out the method steps of the method according to one of claims 1 to 7.

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