Method for determining a motor torque

Abstract

Method for determining a motor torque (24) for controlling a rack actuator of a rack of a steer-by-wire steering system in a vehicle, in which a dynamic model of the rack is used and first a differentially flat output variable is determined, from which the motor torque (24) is determined.

Description

[0001] R. 414974

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for determining engine torque

[0006] The invention relates to a method for determining a motor torque for controlling a rack and pinion actuator in a steer-by-wire steering system in a vehicle, in particular in a motor vehicle, and an arrangement for carrying out the method.

[0007] State of the art

[0008] A steer-by-wire steering system transmits a steering command from a sensor, via one or more control units, exclusively electrically to an electromechanical actuator that executes the steering command. Such a system typically includes a feedback unit, such as a steering wheel actuator (SWA), a steering actuator, for example, a rack and pinion actuator (SRA), and a unit for evaluating and calculating signals, which is implemented, for example, in software or software functions.

[0009] The presented method is used to control a rack and pinion actuator in a vehicle's steer-by-wire steering system. This control serves to set a requested rack position, rotor position, or steering angle position. To set one of these parameters, the rack and pinion actuator includes a servo motor that must be controlled. The control parameter is the requested motor torque of the servo motor in the rack and pinion actuator. In this way, for example, the rack in the steer-by-wire steering system can be positioned as desired.

[0010] Disclosure of the invention R. 414974

[0011] - 2 -

[0012] Against this background, a method with the features of claim 1 and an arrangement according to claim 9 are presented. Embodiments are described in the dependent claims and in the description.

[0013] The presented method is used to determine the motor torque required to control a rack and pinion actuator in a steer-by-wire steering system of a vehicle. The method employs a dynamic model of the rack and pinion and first determines a differentially flat output variable from which the motor torque is calculated.

[0014] Furthermore, a signal representing a specific engine torque can be generated. This embodiment is a method for generating a signal representing a specific engine torque.

[0015] The rack and pinion actuator can then be controlled with the generated signal. This embodiment is a method for controlling a rack and pinion actuator of a steer-by-wire steering system in a vehicle.

[0016] The rack and pinion actuator can be controlled to set a requested rack position, a rotor position of the servo motor, or a steering angle position of a steering handle, in particular a steering wheel.

[0017] The described method thus uses a model presented herein to generate a signal for a motor torque that is to be set.

[0018] The presented method improves the positioning accuracy of the requested reference variable or reference input. Furthermore, the control allows for the separation of the reference and disturbance compensation dynamics. For example, the control parameter G(s) * L(s) can be used to improve the positioning accuracy or the dynamics of the reference behavior, while the controller can be used to adjust the disturbance compensation dynamics. See Figure 1 for the quantities mentioned. R. 414974

[0019] - 3 -

[0020] The presented method uses an algorithm that, in turn, employs the requested reference variable and a modeled system to calculate a motor torque that guides the rack closely to the desired target trajectory. The additional control system then only manages the unmodeled effects, such as disturbances, nonlinearities, etc.

[0021] The presented arrangement serves to carry out the procedure and includes an evaluation unit for this purpose. The arrangement and / or the evaluation unit can be implemented in hardware and / or software and integrated into a vehicle's control unit or designed as such a control unit.

[0022] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0024] Brief description of the drawings

[0025] Figure 1 shows a possible sequence of the presented procedure in a flowchart.

[0026] Figure 2 shows a model of a rack and pinion actuator.

[0027] Figure 3 shows, in a highly simplified, purely schematic form, a vehicle with one embodiment of the presented arrangement.

[0028] Embodiments of the invention R. 414974

[0029] - 4 -

[0030] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0031] Figure 1 shows a flowchart illustrating the sequence of one embodiment of the presented method. The diagram shows transfer functions, in this case in the Laplace domain, L(s) 10, G v (s) 12, K(s) 14 and G x (s) 16.

[0032] From the reference quantity Xd 20, the differential flat output zi,d 22 is obtained using the transfer function L(s) 10. From this, the pilot-controlled motor torque Ud 24 is derived. The control signal for controlling the rack and pinion actuator Tmot 26 is the sum of Ud 24 and Uk 25. From this value, the motor torque T is derived. mot 26. Another quantity is the measured or calculated rack position x rac k 28.

[0033] The approximate behavior of G(s) in Figure 1 is shown in Figure 2.

[0034] Flatness-based feedforward control is a control engineering method based on the concept of flatness. Flatness refers to the property of a system where all state variables and their derivatives can be expressed in terms of the input variables and their derivatives. In flatness-based feedforward control, the system is designed to be flat, meaning it is possible to control the desired state variables and their derivatives using the input variables. This allows for system inversion. This enables the feedforward control of the system to be designed to achieve the desired state variables before the control engineering techniques are applied to compensate for any disturbances.

[0035] The quantities and transfer functions shown are summarized below:

[0036] Xd 20: reference rack position zi,d 22: differential flat output

[0037] Ud 24: requested motor torque calculated via the forward coupling

[0038] Uk 25: Motor torque R calculated by the controller K(s). 414974

[0039] - 5 -

[0040] L(s) 10: Calculation of the flat output signal

[0041] Gv(s) 12: Calculation of Ud

[0042] K(s) 14: Control

[0043] G x (s) 16: Distance from motor torque to rack position

[0044] Xrack 28: measured or calculated rack position

[0045] Tmot 26: Engine torque

[0046] Figure 2 shows a modeled rack and pinion actuator. This model of the rack and pinion actuator is designated with the reference number 50.

[0047] The diagram also shows the following model parameters: the linear stiffness of the servo drive k se rvo 52, the damping of the servo drive d servo 54, the inertia of the rotor JMO 56, the transmission rate of the servomotor iRaMo 57, the rack mass mRa 58 and the externally applied shaft stiffness k ex t 60. An arrow 62 illustrates the size of the rotor angle of the servo motor q> mo t and motor torque of the servo motor T mot Another parameter is the rack force FR964.

[0048] This leads to the following dynamic system: x = A ■ x + b ■ u

[0049] In summary, the following factors should be considered:

[0050] Xi: Rotor position

[0051] X2: Rotor speed or rotational speed

[0052] X3: Rack position

[0053] X4: Rack speed

[0054] JMO 56: Rotor inertia mRa 58: Rack mass R. 414974

[0055] - 6 - k S ervo 52: linear stiffness of the servo drive d Servo54: Servo drive damping dw0: Motor damping iRaMo 57: Servo transmission rate

[0056] To calculate the flat output, the matrix L is first calculated. m educated.

[0057] This matrix is ​​derived from the well-known observation map matrix.

[0058] Q s = [b Ab A 2 b ... A n-1 b] derived.

[0059] The last row of Q s forms the vector l lt which is used to to calculate.

[0060] This is how A and B can be shaped:

[0061] The transformed system is then: z = Ä - z + bu, z = L ■ x.

[0062] Applied to the system from Figure 2, z l d will be calculated. R. 414974

[0063] - 7 -

[0064] Here, the rack speed was replaced by the Laplace-transformed speed.

[0065] V d= S ' X d (s = jüJ) and the rotor position

[0066] The requested engine torque u d can be calculated by: u d = G v (s) ■ z 1>d = (s 4 + a0+ cii ■ s + a2■ s 2 + a3■ s 3 ) ■ z lid with

[0067] Figure 3 shows, in a highly simplified, purely schematic form, a vehicle designated as a whole by the reference numeral 100. This vehicle 100 is equipped with a steer-by-wire steering system 102, which in turn comprises a steering handle 104, e.g., a steering wheel, a device 106 for carrying out the procedure, and a rack 108. R. 414974

[0068] - 8 -

[0069] In the arrangement 106, an evaluation unit 110 is provided, which is implemented by hardware and / or software. A rack actuator 120 is assigned to the rack 108, which in turn includes a servo motor 122 that is controlled and for which a requested motor torque is determined or calculated using the method presented herein.

Claims

R. 414974 - 9 - Claims 1. Method for determining a motor torque (24) for actuating a rack actuator (120) of a rack (108) of a steer-by-wire steering system (102) in a vehicle (100), in which a dynamic model (50) of the rack (108) is used and a differentially flat output quantity is first determined from which the motor torque (24) is determined.

2. Method according to claim 1, wherein a signal representing the specified motor torque (24) is generated.

3. Method according to claim 2, wherein the rack actuator (120) is controlled by the generated signal.

4. Method according to claim 3, wherein the rack actuator (120) is controlled to set a requested rack position.

5. Method according to claim 3, wherein the rack actuator (120) is controlled to set a rotor position.

6. Method according to claim 3, wherein the rack actuator (120) is actuated to set a steering angle position.

7. Method according to any one of claims 1 to 6, wherein the requested motor torque Ud (24) is calculated by: u d = G v (s) ■ z 1>d = (s 4 + a0+ cii ■ s + a2■ s 2 + a3■ s 3 ) ■ z lid with R. 414974 - 10 - 8. Method according to one of claims 1 to 7, in which additional control is carried out, the manipulated variable of which is realized by a feedback of the quantity(s) rack position, motor torque, rotor position and / or steering angle position.

9. Arrangement for determining a motor torque (24) for controlling a rack actuator (120) of a rack (108) of a steer-by-wire steering system (102) in a vehicle (100), wherein the arrangement (106) has an evaluation unit (110) which is configured to carry out a method according to any one of claims 1 to 8.

10. Arrangement according to claim 9, which is integrated into a control unit of the vehicle (100).

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