Method for operating a power steering system

Abstract

Method for operating a power steering system that has a steering handle via which a direction of travel of a vehicle can be influenced and which acts on a rack, the position of which determines the direction of travel, wherein the vehicle is in a state in which the direction of travel is specified using a requested trajectory calculated by the power steering system, after detection of a fault in the power steering system the rack is controlled by a substitute position controller, the control by the substitute position controller is terminated when the driver resumes control of the vehicle and an intervention occurs via the steering handle.

Description

[0001] R. 415012

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating a power steering system

[0006] The invention relates to a method for operating a power steering system and an arrangement for carrying out the method.

[0007] State of the art

[0008] Power steering, also known as assisted steering, reduces the force required to operate steering controls, particularly the steering wheel. This is helpful, for example, when steering while stationary, maneuvering, and at low speeds. Typically, an additional torque is provided by a motor, which compensates for the steering effort applied by the driver.

[0009] In such a power steering system, for example, a rack and pinion drive is used, in which a rack is moved by a pinion turned by the steering handle and then usually moves a tie rod. The movement of this rack, especially its speed, is monitored to ensure the safe operation of the entire power steering system.

[0010] Different levels of automation can be implemented in vehicle operation, depending on the extent to which the driver is assisted in using the vehicle. SAE levels (SAE: Society of Automotive Engineers) are defined to precisely classify the degree of automation, using a scale of six levels. Level 0 corresponds to driving without any automation, and Level 5 corresponds to R. 415012.

[0011] - 2 -

[0012] Full automation. These levels thus classify assisted, automated and autonomous driving (Level 5).

[0013] This section discusses SAE Level 2 and SAE Level 2+ in more detail, where the driver is permitted to remove their hands from the steering handle or steering wheel. In such ferry operations, it must be ensured that safe continuation of the journey is guaranteed even in the event of a system malfunction.

[0014] Disclosure of the invention

[0015] Against this background, a method with the features of claim 1 and an arrangement according to claim 8 are presented.

[0016] Embodiments are derived from the dependent claims and from the description.

[0017] The presented method is used to operate a power steering system that includes a steering handle for influencing the vehicle's direction of travel. This handle acts on a rack whose position determines the direction of travel. In this method, the vehicle is in a state where the direction of travel is specified by a requested trajectory calculated by the power steering system. This corresponds, for example, to SAE Level 2+.

[0018] After a fault is detected in the power steering system, the rack is controlled via a backup position controller. A fault is a condition in which the power steering can no longer be operated safely or even fails completely. The backup position controller is a quality management (QM) consumer, meaning it is not classified as a safety-critical component.

[0019] The control via the substitute position controller is aborted when the driver regains control of the vehicle and an intervention is made via the steering handle.

[0020] The presented procedure provides that, in the event of a power steering failure, the "Damping Mitigation Measure" is replaced by the "Switching to a Substitute Position Controller" measure. This is a QM-R. 415012.

[0021] - 3 -

[0022] Consumers without safety rating or protection. Therefore, it is only used for a limited period, e.g., 2.5 seconds.

[0023] The presented arrangement serves to carry out the procedure and includes an evaluation unit configured for this purpose. The arrangement and / or the evaluation unit is / are implemented in hardware and / or software. The arrangement can be integrated into a vehicle control unit or be designed as such a control unit.

[0024] The presented method ensures that the requested trajectory is followed at least for a limited period of time, unlike other methods which dampen the rack movement, preventing jerky movement but allowing the movement itself.

[0025] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0026] 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.

[0027] Brief description of the drawings

[0028] Figure 1 shows a vehicle at vehicle level in a block diagram.

[0029] Figure 2 shows a steering control unit in a block diagram.

[0030] Figure 3 shows an embodiment of the presented safety mechanism in a block diagram.

[0031] Figure 4 shows a simplified flowchart of a possible sequence of the presented procedure. R. 415012

[0032] - 4 -

[0033] Figure 5 shows a schematic, highly simplified representation of a vehicle with one embodiment of the described arrangement.

[0034] Embodiments of the invention

[0035] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0036] Figure 1 shows a block diagram illustrating the basic structure of a vehicle at the vehicle level. The diagram shows sensors 12, a vehicle state 14, an SAE L2+ vehicle control system 16, a driver monitoring system 18, a human-machine interface (HMI) 20, a driver 22, a powertrain control system 24, a powertrain 26, a brake system 28, a steering control system 30, and a steering system 32.

[0037] Figure 1 illustrates in particular the specific problem that arises during driver monitoring when SAE L2 is switched on and interacts with the driver.

[0038] Figure 2 shows a block diagram of the structure of a steering control unit (SCU), designated by the reference numeral 100. The diagram shows a main microcontroller 102, a backup system 104, a power stage 106, a selective phase separator 108, and a motor 110, to which a first rotor position sensor 112 and a second rotor position sensor 114 are assigned.

[0039] The task of the backup system is to take over the control task of the "Keep Last Angle" (KLA) safety mechanism in the event of a failure of the main microcontroller 102, i.e., in the event of a serious error.

[0040] The procedure is carried out, for example, with a fail-safe or fault-tolerant steering system that uses a KLA function (KLA: Keep Last Angle) as a preventive measure, e.g., on a backup R. 415012

[0041] - 5 -

[0042] The microcontroller is implemented. The system response to a single-point fault should be as follows: switching to the backup microcontroller, maintaining the last rotor position for at least 2.5 seconds, and requesting the driver to regain control of the vehicle. This applies specifically only to a serious fault of the main microcontroller 102. Otherwise, "gentler" measures can also be initiated, see 254 in Figure 3. It should be noted that the response to a single-point fault depends on the fault itself.

[0043] Figure 3 shows in a block diagram a safety mechanism, which is generally designated by the reference number 200 and which represents an implementation of the presented procedure.

[0044] The illustration shows a vehicle control unit 202 that inputs a requested rack position 203 and an actual rack position 204 into a comparator 206. The result of the comparison is referred to as the rack position deviation 208 and is input into a computing unit 210 for calculating a nominal rack torque 212 and a computing unit 214 for calculating rack speed limits, i.e., the limit values ​​216.

[0045] The transmission of the requested rack position 203 to the computing unit 214 is only required for asymmetric speed limits.

[0046] The nominal rack torque 212 is compared with a torsion bar torque 222 in a comparator 220. The result is input into a torsion bar torque PID controller 224. This represents a position controller that incorporates a steering torque for improved driving feel and is no longer ASII-D compliant. A steering motor torque 230 is output.

[0047] The steering motor torque 230 is input into a rack and pinion speed limiter 232, as are the rack and pinion speed limiters 216. The R. 415012

[0048] - 6 -

[0049] Speed ​​limiter 232 outputs a signal "limited motor torque" 234 to a crossfader 240. Furthermore, block 214 outputs the rack speed limits 216 to a rack speed monitor 238.

[0050] The crossfade controller 240 receives a "Trigger-KLA 250" signal from a state machine 252 to clear a condition. A "Rack and pinion speed limiter" signal 216 from block 214 goes to a "Rack and pinion speed monitoring" block 238. From this block 238, a "Trigger substitute position controller" signal 239 goes to a substitute position controller 260, from which a "Motor torque" signal 258 is in turn given to the crossfade controller 240.

[0051] A motor torque 270 in ASIL-D is output to a power stage 272, which in turn outputs a rack movement 274.

[0052] The measure presented herein is given by the signal “Trigger- Replacement Position Controller” 239, with which the replacement position controller 260 is activated or triggered.

[0053] This measure is intended to prevent the use of a damaged QM position controller. Therefore, the controller path is switched to a basic substitute position controller. This is based on the fact that a damping measure alone is insufficient to prevent movement in the wrong direction.

[0054] The proposed measure, in conjunction with the replacement position controller, can fulfill the following tasks in its configuration:

[0055] 1. Triggering visual warning signals to ensure that the driver regains control,

[0056] 2. Triggering the replacement position controller using the following methods: R. 415012

[0057] - 7 -

[0058] Following the requested trajectory, if the requested trajectory becomes invalid, the system can hold the last position (KLA: Keep Last Angle).

[0059] Ramping back to the zero position of the rack.

[0060] The replacement position controller can be deactivated again, for example, by DH or a bus.

[0061] Figure 4 shows a highly simplified flowchart of the presented procedure. In the first step, 450, a vehicle equipped with power steering begins to travel. In step 452, a fault occurs. In step 454, the driver is warned, in this case by a visual and audible warning signal. In step 456, the system switches to a backup position controller, which actuates the rack and pinion for a limited period. This action continues for a predetermined time and ends before the driver regains control of the vehicle, i.e., when their hands are back on the steering handles and they are actively steering.

[0062] Figure 5 shows a purely schematic representation of a vehicle designated by the reference numeral 500. The vehicle 500 has a power steering system 502, which in turn comprises a rack 504, a steering handle 505, and a substitute position controller (507). Furthermore, an arrangement 506 is provided, which is configured to carry out the presented method and for this purpose includes an evaluation unit 508.

Claims

R. 415012 - 8 - Claims 1. Method for operating a power steering system (500) which has a steering handle (505) by which the direction of travel of a vehicle (500) can be influenced and which acts on a rack (504) whose position determines the direction of travel, wherein the vehicle (500) is in a state in which the direction of travel is specified by a requested trajectory calculated by the power steering (502), After detecting a fault in the power steering (502), the rack (504) is controlled via a substitute position controller (260, 507). The control via the substitute position controller (260, 507) is aborted when the driver regains control of the vehicle (500) and an intervention via the steering handle (505) takes place.

2. Method according to claim 1, wherein, after the fault is detected, a warning signal is first given to the driver.

3. Method according to claim 2, wherein an optical and / or acoustic warning signal is emitted.

4. Method according to one of claims 1 to 3, wherein the substitute position controller (260, 507) controls the rack (504) such that the direction of travel corresponds to the requested trajectory.

5. Method according to claim 4, wherein it is checked whether the requested trajectory leads to an invalid rack position. R. 415012 - 9 - 6. Method according to claim 6, wherein, when an invalid rack position is detected, the last valid rack position is maintained.

7. Method according to any one of claims 1 to 6, which is carried out during a drive at SAE Level 2+.

8. Arrangement for operating a power steering system with a unit configured to carry out a method according to any one of claims 1 to 7.

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