Power boost when steering system performance is degraded

Abstract

The present invention is a method for controlling a steering system (1) for a road vehicle, characterized in that it comprises the following steps: a) determining a state of a performance level of the steering system (8); b) determining a vehicle situation (9); c) determining in a decision making unit (10) whether the performance of the steering system at the determined state of the performance level is likely to be sufficient for the determined vehicle situation; d) if it is determined that the performance of the steering system is most likely to be insufficient, changing the state of the performance level by reducing the performance level for a short period of time (11).

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a steering system of a road vehicle according to the preamble of claim 1. [Background technology]

[0002] In automobiles with electromechanical steering systems, performance degradation can occur and is tolerated. For steering systems in autonomous vehicles and / or steer-by-wire systems, the requirements and architectures are different. One of the main requirements is that the steering system must be fault tolerant, meaning that if a fault occurs, the steering system must still operate and provide its primary function.

[0003] If degradation occurs in any part of the steering system, the primary function may not be sufficient for full steering function in all driving situations. For example, if one side of a redundant architecture is suddenly switched off or the system is suddenly degraded, there may not be enough power to complete the steering maneuver, which may be insufficient if the maneuver is an emergency maneuver. Summary of the Invention

[0004] It is an object of the present invention to provide a method for controlling the steering system of a road vehicle which makes it possible to steer the vehicle in all driving situations even after a degradation in the performance of the steering system.

[0005] This object is achieved by a method for controlling a steering system of a road vehicle having the features of claim 1.

[0006] Accordingly, there is provided a method of controlling a steering system for a road vehicle, the method comprising the steps of: a) Determine the state of the steering system's performance level; b) Determine the vehicle status; c) determining in a decision making unit whether the performance of the steering system at the determined state of performance level is likely to be sufficient for the determined vehicle situation; d) If the steering system performance is insufficient, change the performance level state by reducing the performance level for a short period of time.

[0007] This method allows the steering system to provide sufficient power for all vehicle situations, even if the steering system is degraded, so that the vehicle can be steered even in situations that require high performance, such as emergency handling.

[0008] Preferably, the vehicle situation determined in step b) is an emergency situation of the road vehicle, which has high performance requirements.

[0009] It is advantageous if in step d) the performance level is reduced to a level that has sufficient performance of the steering system to provide full steering functionality for the vehicle situation.

[0010] To prevent damage to the steering system, the reduction in performance level in step d) is only carried out for a period of time short enough to allow for changing vehicle conditions.

[0011] The determination of the vehicle situation in step b) may be based on one or more of the following vehicle parameters: vehicle speed, lateral acceleration, longitudinal acceleration, yaw rate, and / or feedback actuator signals and / or road wheel actuator signals.

[0012] In step d) a change in performance level can be implemented depending on the state of the performance level of the steering system.

[0013] Preferably, in step d) the performance level is gradually reduced.

[0014] The rate of decrease is an adjustable parameter and / or it can depend on the vehicle speed.

[0015] The performance level is reduced to a limit value, which is preferably an adjustable parameter and depends on the original performance level and / or vehicle speed.

[0016] Preferably, in step d), the time period is an adjustable parameter, which depends on the original performance level and / or the vehicle speed.

[0017] In an advantageous embodiment, after step d), the performance level is increased back to the original performance level determined in step a), where the rate of increase after step d) is an adjustable parameter and / or it can depend on the vehicle speed.

[0018] There is further provided a steer-by-wire steering system or electric power steering system for a road vehicle having a controller arranged to implement the above-described method. [Brief explanation of the drawings]

[0019] Preferred embodiments of the present invention will now be described with reference to the drawings. [Figure 1] FIG. 1 is a schematic diagram of a steer-by-wire steering system. [Figure 2] FIG. 2 is a block diagram illustrating a method for controlling a steering system. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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 road wheels 4. A road wheel actuator 5 actuates a gear rack 6 by means of a recirculating ball gear 7.

[0021] When the driver operates the steering wheel 3, the steering axis 2 is rotated, which is detected by an axis sensor (not shown in the figure). The control unit calculates an actuation signal for the road wheel actuator 5 from the signal detected by the axis sensor. By actuating the gear rack 6 with the actuation signal, the road wheels 4 are changed direction. At the same time, the force introduced from the road wheels 4 to the gear rack 6 is detected by another sensor (not shown in the figure), and a feedback signal is calculated, which is applied to the steering axis 2 by a steering wheel actuator 7, also called a feedback actuator, so that the driver can perceive feedback at the steering wheel 3.

[0022] If a malfunction occurs in the system, performance degradation may occur. The performance degradation may result in a reduced performance level of the steering system. Depending on the degraded functionality, the system may be unable to perform the current driving maneuver in a particular performance mode and may, for example, have to terminate it.

[0023] According to the method shown in Figure 2, a performance mode (performance level or performance class) or state 8 and a current vehicle situation or vehicle operation 9 are determined. The information is sent to a decision making unit 10, which analyzes whether the performance of the steering system in the determined performance mode (performance level or performance class) or state is sufficient for the vehicle situation or vehicle operation. If the performance available in the determined performance mode (performance level or performance class) or state is too low, the performance level is gradually reduced, which increases the performance of the steering system to the minimum required for the current vehicle situation or vehicle operation. This performance level change 11 is performed for a short period of time sufficient to end the operation, especially an emergency situation.

[0024] In particular, the vehicle situation or vehicle operation determination 8 can be based on vehicle parameters such as vehicle speed, lateral acceleration, longitudinal acceleration, yaw rate, etc. Whether the vehicle is in a high performance demanding situation can be determined based on steering system internal parameters such as feedback actuator and / or road wheel actuator parameters, e.g., angle, angular velocity, reference and / or expected motor torque and measured or expected driver torque, which can also be used for situation determination.

[0025] A performance level change 11 can be implemented depending on the degraded state of the steering system. For example, at least one portion of the system can be switched off or downgraded to zero power. Other portions of the system would then be changed to provide more power. If all portions of the system are operational but in a degraded mode, the performance levels of all portions of the system would be changed to provide more power.

[0026] The performance level can then be gradually reduced to gradually increase the available power. The rate of reduction can be an adjustable parameter and / or it can depend on the vehicle speed. The limit value for the reduction can likewise be an adjustable parameter, which can depend on the original performance level and / or the vehicle speed.

[0027] The modified lower performance level can be applied temporarily for a short period of time. The time period is an adjustable parameter, which depends on the original performance level and / or the vehicle speed. After the aforementioned time period has elapsed, the performance level is gradually increased to the original value, resulting in a reduction in available power. The rate of increase is an adjustable parameter and / or it can depend on the vehicle speed.

[0028] Although changing the performance level may damage the system, it allows for maintaining operability in all conditions by increasing the power level of the steering system in situations requiring high performance, such as emergency handling.

Claims

1. A method of controlling a steering system (1) for a road vehicle experiencing a deterioration in steering system performance, characterized in that the method comprises the steps of: a) determining a state of degradation of the steering system (8); b) determining the vehicle status (9); c) if the vehicle situation determined in step b) is a road vehicle emergency situation, determining in a decision making unit whether a power level of the steering system in the determined degraded performance state is likely to be sufficient for the determined vehicle situation (10); d) if it is determined that the power level of the steering system is likely to be insufficient, increasing the power level of the steering system to a level having sufficient performance to provide full steering function for the vehicle situation by relaxing constraints on the performance of the steering system for a short period of time (11).

2. 2. The method of claim 1, wherein the relaxing of the constraints on the steering system performance in step d) is performed for a period of time short enough to allow the vehicle situation to change.

3. 2. The method of claim 1, wherein the determination of the vehicle situation in step b) is based on one or more of the following vehicle parameters: vehicle speed, lateral acceleration, longitudinal acceleration, yaw rate, and / or feedback actuator parameters and / or road wheel actuator parameters.

4. 2. The method according to claim 1, wherein in step d) the relaxation of the restrictions on the performance of the steering system is performed depending on the state of the performance degradation of the steering system.

5. 2. The method of claim 1, wherein in step d) the constraints on the performance of the steering system are gradually relaxed.

6. 6. The method of claim 5, wherein the rate of relaxation is an adjustable parameter and / or it depends on the vehicle speed.

7. 2. The method according to claim 1, wherein in step d) the time period is an adjustable parameter, which depends on the original performance degradation state and / or the vehicle speed.

8. 2. The method of claim 1, wherein after step d), the limitations on the steering system performance are returned to their original levels.

9. 9. The method of claim 8, wherein the speed of return of the limitations on the performance of the steering system to the original level after step d) is an adjustable parameter and / or it can depend on the vehicle speed.

10. A steer-by-wire steering system (1) or electric power steering system for a road vehicle having a controller arranged to implement the method according to any one of claims 1 to 9.

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