Power saving mode for motor vehicle steering system

Abstract

The invention relates to a method for saving power in a steering system (1) of a motor vehicle, said steering system comprising a wheel actuator (5) acting on a rack (6) for turning a steerable wheel (4) and a control unit (10) for calculating an operating signal for the wheel actuator (5), wherein the control unit (10) comprises a position controller for calculating a motor torque request depending on an actual position or / and a measured position of the rack (6) and a requested rack position, wherein the method comprises the following steps: detecting a passive mode of the steering system (1) by a passive mode detection unit being part of the control unit (10) if the motor vehicle is stopped and no steering input is provided; and setting the motor torque request to zero for saving power in case the passive mode detection unit detects a passive mode.

Description

Technical Field

[0001] The present invention relates to a method for saving power in the steering system of a motor vehicle as described in the preamble of claim 1. Background Technology

[0002] In a steering-by-wire system, there is no mechanical connection between the steering wheel, the steering rack, and the steerable wheels. Feedback actuators acting on the steering wheel provide feedback to the driver. Steering motion is achieved by an electrically controlled motor, which is part of the wheel actuators acting on the steering rack. A position controller moves the steering rack to the desired position, thereby achieving the desired wheel angle. The position controller operates such that the wheel actuators follow a reference position signal. The position controller remains active even when the vehicle is stationary and the driver provides no steering input. Therefore, the power consumption of the steering system and the thermal load on the motor and electronic control unit (ECU) remain high. Consequently, the electrical components reach their end-of-life more quickly. Summary of the Invention

[0003] Therefore, the object of the present invention is to provide a method for saving power in a steering system, which reduces the thermal load on the motor of the wheel actuator and its electronic control unit.

[0004] This objective is achieved by a method having the features of claim 1.

[0005] This invention provides a method for saving power in a steer-by-wire system or an electric power steering system of a motor vehicle. The steering system includes a wheel actuator acting on a rack and a control unit. The wheel actuator is used to rotate a wheel. The control unit calculates an operating signal for the wheel actuator. The control unit includes a position controller that calculates a motor torque request based on the actual or estimated position of the rack and a requested rack position. The power-saving method includes the following steps:

[0006] If the vehicle stops and no steering input is provided, the passive mode of the steering system is detected by the passive mode detection unit, which is part of the control unit; and

[0007] When the passive mode detection unit detects a passive mode, the motor torque request is set to essentially zero to save power.

[0008] The passive mode results in reduced power consumption in the steering system. Furthermore, the system does not heat up, which extends the lifespan of electrical components.

[0009] In a first embodiment, the motor torque request is set to zero using a torque limiter, which gradually limits the motor torque request to zero upon detection of the passive mode. Advantageously, if a signal from the passive mode detection unit indicates that the vehicle is activated and the passive mode no longer exists, the torque limiter gradually increases the limit value to a predetermined maximum value.

[0010] In the second embodiment, the motor torque request is set to zero by modifying the request position of the rack. Preferably, if a signal from the passive mode detection unit indicates that the vehicle is activated and the passive mode no longer exists, the request position of the rack is gradually modified by gradually changing the previous modification of the request position of the rack to essentially zero.

[0011] Furthermore, a steer-by-wire system for a motor vehicle is provided, the steer-by-wire system being designed to perform the aforementioned methods. The rack of the steer-by-wire system is part of the front or rear axle. The controller unit is preferably located next to the wheel actuators.

[0012] Generally, steering input can be provided by the driver, for example by turning the steering wheel or acting on the steering mechanism, or by the vehicle control unit used for autonomous vehicle control. Attached Figure Description

[0013] Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0014] Figure 1 This is a schematic diagram of a steer-by-wire system for a motor vehicle;

[0015] Figure 2 The time dependence of motor torque limitation and finite motor torque is shown; and

[0016] Figure 3 The diagram shows the operation mode plotted according to time.

[0017] Figure 1 This is a schematic diagram of a steer-by-wire system 1, which includes a steering shaft 2 connected to a steering mechanism 3. There is no mechanical connection between the steering mechanism 3 and the wheels 4. Wheel actuators 5 operate a rack 6 via a rack and pinion transmission 7, the rack being part of the front axle 8. The front axle 8 has two linkages 9 for the wheels 4, with only one wheel 4 shown in the diagram. Detailed Implementation

[0018] When the driver operates the steering mechanism 3, the steering shaft 2 rotates, which is detected by an axle sensor (not shown in the figure). When the vehicle starts, the control unit 10, located next to the wheel actuator 5, calculates the operating signal for the wheel actuator 5 based on the signal detected by the axle sensor. By operating the rack 6 with the operating signal, the front wheel axle 8 moves laterally, and the wheel 4 rotates. Simultaneously, the force introduced from the wheel 4 into the wheel axle 8 is identified by another sensor (not shown in the figure), and a feedback signal is calculated. This feedback signal is applied to the steering shaft 2 via the feedback actuator 11, thereby allowing the operator to perceive the feedback from the steering mechanism 3.

[0019] The control unit 10 includes a position controller that calculates the motor torque request based on the actual and / or measured position of the rack 6, and the requested rack position. Therefore, the wheel actuator 5 follows the reference position signal.

[0020] In a passive state, it is not necessary to track the position of rack 6. A vehicle is considered to be in a passive state if the following conditions are met:

[0021] The vehicle stops (the vehicle speed is zero and the speed of the drive wheels is zero); and

[0022] The driver did not provide steering input.

[0023] Under these conditions, position control can be disabled, thus entering power-saving mode. Power-saving mode is achieved through near-zero torque requests. Near-zero requests for the wheel actuator motor torque can be achieved by applying a torque limiter to the requested motor torque. "Near-zero" implies the existence of hardware-related inaccuracies, and that even if the request is set to zero, there may still be residual motor torque requests.

[0024] Figure 2 and Figure 3 Two schematic diagrams are shown. Figure 2 The diagram illustrates the motor torque limit (dashed line) given by the limiter and the relationship between the resulting finite motor torque (solid line) and time. Figure 3 The operating modes corresponding to time are shown, where "OFF" represents the normal operating mode and "ON" represents the power saving mode.

[0025] The torque limiter reads the requested motor torque, calculated from the position controller and signals from the passive mode detection unit. If the signal from the passive mode detection unit indicates that the vehicle is in passive mode, the torque limiter gradually decreases the limit value until it reaches zero. The requested motor torque follows the limit value and is limited to zero torque. If the signal from the passive mode detection unit indicates that the vehicle is activated and passive mode is no longer present, the torque limiter gradually increases the limit value to a predetermined maximum value. The requested motor torque again follows the limit value until the limit value no longer affects the requested motor torque.

[0026] By modifying the requested motor torque, it is possible to further achieve zero-request motor torque for the wheel actuator.

[0027] If a passive mode is detected, the signal from the passive mode detection unit causes the modification controller to adjust the requested position of the rack. The modification controller adjusts the position increment for the actual wheel actuator motor torque output. The integrated position increment, along with the original position request, generates a modified position request. This modified position request does not require maintaining the position controller's output, and therefore does not require requesting torque from the motor. The position controller receives the modified requested position, the actual position of the rack, and further information, and calculates the torque request based on this information, which gradually decreases to zero over time.

[0028] If a signal from the passive mode detection unit indicates that the vehicle is activated and the conditions for passive mode are no longer met, the requested position will not be modified, and the torque request will be based on the actual requested position.

[0029] Both implementations share the characteristic that the torque request is set to zero, which reduces the power consumption of the steering system and hinders the system's heating.

[0030] This invention is also applicable to rear-wheel steering systems, wherein the wheel actuator is located on the rear axle of a motor vehicle. This wheel actuator can also be implemented to move a steering rack to a desired position, thereby steering the rear wheels.

[0031] This invention is also applicable to electric power steering (EPAS) systems with an external drive interface for motor vehicles. This steering actuator can also be implemented to move the steering rack to the desired position, thereby steering the wheels.

Claims

1. A method for saving power in a steering system (1) of a motor vehicle, the steering system comprising a wheel actuator (5) acting on a rack (6) and a control unit (10), the wheel actuator (5) for rotating a steerable wheel (4), the control unit (10) calculating an operating signal for the wheel actuator (5), wherein, The control unit (10) includes a position controller, which calculates the motor torque request based on the actual position and / or measured position of the rack (6) and the requested rack position. The method comprises the following steps: If the vehicle stops and no steering input is provided, the passive mode of the steering system (1) is detected by the passive mode detection unit, which is part of the control unit (10); and When the passive mode detection unit detects the passive mode, the motor torque request is set to essentially zero to save power.

2. The method according to claim 1, characterized in that, By using a torque limiter to set the motor torque request to essentially zero, when the passive mode is detected, the torque limiter gradually restricts the motor torque request to essentially zero.

3. The method according to claim 2, characterized in that, If a signal from the passive mode detection unit indicates that the vehicle is activated and the passive mode is no longer present, the torque limiter gradually increases the limit value to a predetermined maximum value.

4. The method according to claim 1, characterized in that, By modifying the request position of the rack (6), the motor torque request is set to essentially zero.

5. The method according to claim 4, characterized in that, If a signal from the passive mode detection unit indicates that the vehicle is activated and the passive mode no longer exists, the requested position of the rack is gradually modified by gradually modifying the previous modification of the requested position of the rack to essentially zero.

6. A steer-by-wire system (1) for a motor vehicle, designed to perform the method according to claims 1 to 5.

7. The steer-by-wire system according to claim 6, characterized in that, The rack (6) is part of the front axle (8) or the rear axle.

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