How to control a car's steer-by-wire steering system with increased feedback torque after a steering system failure.

Abstract

A method for controlling a steer-by-wire steering system (1) of a road vehicle, the steer-by-wire steering system (1) comprising a feedback actuator (8) for applying a feedback torque to a steering wheel (3), and a road wheel actuator (5) for steering steerable road wheels (4) each having two redundant power packs, characterized in that the method comprises the following steps: if a fault is detected in the road wheel actuator (11), increasing (10) the feedback torque provided by the feedback actuator (8) to a value higher than a calculated feedback torque; if a fault is detected in one power pack of the feedback actuator (8) or a fault in one power pack of the feedback actuator (8) is detected (9), increasing (10) the feedback torque provided by a functional power pack of the feedback actuator to a value higher than the calculated feedback torque.

Description

【Technical Field】 【0001】 The present invention relates to a method for controlling a steer-by-wire steering system of a motor vehicle as described in the preamble of claim 1, and to a steer-by-wire steering system designed to implement such a method. 【Background Art】 【0002】 In motor vehicles, it is known to implement a fail function architecture for a steer-by-wire steering system. These include two identical power packs each containing a separate independent controller and motor. Defects or degradations of the system have to be reported to the driver, for example, by providing feedback by means of a feedback actuator. If a defect or degradation occurs in the feedback actuator, there is a risk that a feedback torque higher than the normal level is applied. If such a situation persists, it may cause high degradation, which is not desirable for system operation. Alternatively, if a defect on one side of the redundant system is the cause, it may lead to degradation of the remaining functional side of the system. 【Summary of the Invention】 【0003】 It is an object of the present invention to provide a method for controlling a steer-by-wire steering system of a motor vehicle that enables providing feedback to the driver in case of degradation or defect of the system without the risk of further degradation or defect. 【0004】 This object is achieved by a method for controlling a steer-by-wire steering system of a motor vehicle having the features of claim 1, and by a steer-by-wire steering system for a road vehicle designed to implement such a method. 【0005】 Accordingly, a method for controlling a steering system of a road vehicle is provided, wherein the steer-by-wire steering system includes a feedback actuator for applying feedback torque to the steering wheel and a road wheel actuator for changing the direction of steerable road wheels, each having two overlapping power packs, and the method is characterized by including the following steps: a) If a defect is detected in the load wheel actuator, increase the feedback torque supplied by the feedback actuator to a value higher than the calculated feedback torque, preferably up to +6 Nm; b) If a defect is detected in the power pack of one of the feedback actuators, the feedback torque supplied by the power pack on which the feedback actuator is functioning is increased to a value higher than the calculated feedback torque. 【0006】 This method allows the driver to be notified of a malfunction in the steering system without the risk of further deterioration or failure. No additional components are required. 【0007】 If a problem such as actuator overheating occurs, the feedback torque can be increased for a specified period of time, and then reduced to a calculated torque. Preferably, the reduction in feedback torque is done gradually. 【0008】 In terms of component types and costs, it is advantageous if the two power packs of the road wheel actuator are identical. 【0009】 This method may further include the following steps: c) If the defect detected in step a) is on one side of the overlapping load wheel actuator, switch off that side and provide at least partial steering function to the remaining functional side. 【0010】 Furthermore, a steer-by-wire steering system for road vehicles designed to implement the above method is provided. 【0011】 This objective is achieved by a method for controlling a steer-by-wire steering system of an automobile having the features of claim 1, and by a steer-by-wire steering system designed to carry out such method. [Brief explanation of the drawing] 【0012】 Preferred embodiments of the present invention will be described with reference to the drawings. [Figure 1] Figure 1 is a schematic diagram of a steer-by-wire steering system in an automobile. [Figure 2] Figure 2 shows a block diagram illustrating how a feedback actuator provides feedback to the driver in the event of a steering system malfunction. [Modes for carrying out the invention] 【0013】 Figure 1 is a schematic diagram of a steer-by-wire steering system 1 having a steering shaft 2 connected to a steering wheel 3. There is no mechanical connection between the steering wheel 3 and the load wheel 4. A load wheel actuator 5 acts on a gear rack 6 via a rack and pinion gear 7. 【0014】 When the driver operates the steering wheel 3, the steering shaft 2 rotates, which is detected by a shaft sensor (not shown in the diagram). The control unit calculates an actuation signal for the load wheel actuator 5 from the signal detected by the shaft sensor. By acting on the gear rack 6 with the actuation signal, the load wheel 4 is turned. At the same time, the force introduced from the load wheel 4 to the gear rack 6 is recognized by another sensor (not shown in the diagram), and a feedback signal is calculated, which is applied to the steering shaft 2 by the steering wheel actuator 8, also called the feedback actuator, so that the driver can perceive feedback in the steering wheel 3. 【0015】 The load wheel actuator 5 and the feedback actuator 8 each have two overlapping power packs (not shown), which may be of the same or different design. 【0016】 Figure 2 schematically illustrates the control method of the steer-by-wire steering system 1. If a failure of a feedback actuator is detected on one side of the overlapping system 9, the motor corresponding to that side is switched off. To provide feedback to the driver, the control unit is informed of the change in state, and the motor control unit increases the feedback torque of the functioning motor to a value higher than the calculated torque (an adjustable parameter) 10, which can be noticed by the driver. After a period of time, the feedback torque is gradually reduced to the calculated torque to reliably avoid thermal loads. If no problems such as overheating occur, the increased torque can be maintained for a long period of time, for example, until the vehicle reaches a repair shop. 【0017】 If a fault is detected in the load wheel actuator, the feedback torque of the feedback actuator is also increased. The fault may be, for example, on one side of the overlapping system, which is then switched off, and the remaining functioning side takes over the steering function at least partially. To inform the driver of a fault in the load wheel actuator, the motor control unit increases the feedback torque of the feedback actuator to a value (adjustable parameter) higher than the calculated torque. After a period of time, the feedback torque may be gradually reduced to the calculated torque if a problem such as overheating occurs.

Claims

[Claim 1] A method for controlling a steer-by-wire steering system (1) of a road vehicle, wherein the steer-by-wire steering system (1) includes a feedback actuator (8) for applying feedback torque to a steering wheel (3) and a road wheel actuator (5) for changing the direction of a steerable road wheel (4), the feedback actuator (8) and the road wheel actuator (5) each have two duplicate power packs, each of which includes a separate independent motor and a separate independent controller, the separate independent controllers included in each of the two duplicate power packs of the feedback actuator (8) each calculate an operating signal for the feedback actuator (8), and the separate independent controllers included in each of the two duplicate power packs of the road wheel actuator (5) each calculate an operating signal for the road wheel actuator (5), the method comprising the following steps: a) If a defect is detected in the load wheel actuator (11), the feedback torque provided by the feedback actuator (8) is increased to a value higher than the calculated feedback torque (10); b) If a partial defect is detected in one of the power packs of the feedback actuator (8) or if a complete defect is detected in one of the power packs of the feedback actuator (8) (9), the feedback torque supplied by the power pack on which the feedback actuator is functioning is increased to a value higher than the calculated feedback torque (10). However, if the temperature of the feedback actuator (8) exceeds a predetermined value, the feedback torque is increased for a specified time, and thereafter the feedback torque is reduced to the calculated torque. [Claim 2] The method according to claim 1, characterized in that the reduction of the feedback torque is performed gradually. [Claim 3] The method according to claim 1, characterized in that the two power packs of the load wheel actuator (5) are identical. [Claim 4] The method according to claim 1, characterized in that it includes the following steps: c) If the defect detected in step a) is on one side of the overlapping load wheel actuator (5), switch off that side and provide at least partial steering function to the remaining functional side. [Claim 5] A steer-by-wire steering system (1) for a road vehicle designed to carry out the method described in claim 1.

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