Method for operating a power steering system

Abstract

A 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 which is provided; after detection of a fault in the power steering system, the rack is moved towards a zero position, the movement of the rack towards the zero position is terminated when the driver resumes control of the vehicle and an intervention occurs via the steering handle.

Description

[0001] R. 415010

[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. 415010.

[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 wheel handles. 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] In the event of a power steering malfunction, it is necessary to inform the driver of this malfunction and, if necessary, to put the vehicle into a condition in which there is no danger to other road users and the driver is not impaired.

[0015] One way to address this, for example, to prevent a communication failure with the higher-level control unit (Figure 1, reference numeral 16), is the KLA (Keep Last Angle) measure. As a first step, the driver is informed of the error. This is done, for example, with an acoustic and / or visual signal. This mechanism is also used in the event of a failure of the main microcontroller, e.g., due to the critical task overflow error. In this case, the system switches to the backup microcontroller, which itself does not have bus communication.

[0016] In a second step, the last position or angle (KLA) on the rack is maintained until the driver regains control of the vehicle. If this takeover does not occur within a predetermined time period, e.g., within 2 seconds, manual steering can be activated and further measures can be taken.

[0017] This procedure is necessary to prevent a sudden return of the steering to straight-ahead driving, especially when cornering.

[0018] Disclosure of invention R. 415010

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[0020] Against this background, a method with the features of claim 1 and an arrangement according to claim 9 are presented. Embodiments are derived from the dependent claims and from the description.

[0021] The presented method is used to operate a power steering system that includes a steering handle. This handle is used to influence the direction of travel of a vehicle in which the power steering system is located and 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 predetermined by a requested trajectory, typically provided by a trajectory controller. That is, in this case, the driver's hands are not on the steering handle or the steering wheel; the driver does not intervene via the steering handle and therefore does not influence the direction of travel. This is also referred to as SAE Level 2+, where the power steering system takes over tasks previously performed by the driver.

[0022] Upon detection of a power steering fault, the rack is now moved towards the zero position in a controlled manner with a specific, adjustable gradient. A fault signifies a condition in which the power steering no longer operates reliably. The zero position of the rack is the position in which the vehicle travels straight ahead. This procedure specifically addresses the KLA fault response. This response is activated as described above, i.e., in the event of a communication failure or when switching to the backup microcontroller in the event of a critical fault on the main microcontroller.

[0023] The movement of the rack towards the zero position is aborted when the driver regains control of the vehicle and intervenes via the steering handles. This means that the driver's hands are once again on the steering handles.

[0024] A warning signal is typically given to the driver before the rack and pinion move. This occurs as soon as possible after the fault occurs. If the driver reacts immediately to this warning signal, as indicated by R. 415010

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[0026] If he has his hands back on the steering handle and is actively steering, then it may not be necessary to trigger the movement of the rack towards the zero position.

[0027] If the driver does not react to the signal conveyed by moving the rack and the rack has been returned to the zero position, then further measures may need to be taken.

[0028] The presented method thus provides, in one embodiment, that when a fault in the power steering is detected, information is first sent to the driver, which includes, for example, an acoustic and / or optical signal.

[0029] For this purpose, a warning light or a bell, for example, can be used. In a second step, the rack is moved to the zero position by activating the associated motor. This can be done, for example, incrementally or continuously, with the rack position typically following a ramp. This ramping back can occur immediately after the fault is detected or after a predetermined period, e.g., 1 second or less. The rack continues to move back until the driver regains control of the vehicle, i.e., resumes steering and thus has their hands back on the steering handle or steering wheel. If the driver does not regain control within a predetermined period, e.g., within 2 seconds, further measures can be initiated.

[0030] For example, the system switches to manual steering. It should be noted that this procedure can be used in conjunction with SAE Level 2+. This means the driver is responsible for taking over in the event of an error. The "ramping to straight-ahead driving" measure serves as an incentive for the driver to take over.

[0031] This prevents the steering from jerking back during cornering or from snapping back.

[0032] In particular, the procedure is effective if the first step, warning the driver with a signal, is ineffective. The driver receives warning via the re-ramming of the rack and the corresponding movement of the R. 415010.

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[0034] The steering mechanism provides an additional incentive. The resulting movement of the vehicle is clearly perceptible.

[0035] 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.

[0036] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0037] 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.

[0038] Brief description of the drawings

[0039] Figure 1 shows a vehicle at vehicle level in a block diagram.

[0040] Figure 2 shows a steering control unit in a block diagram.

[0041] Figure 3 shows an embodiment of the presented safety mechanism in a block diagram.

[0042] Figure 4 shows in a graph the progression of the rack position in one embodiment of the presented method.

[0043] Figure 5 shows a flowchart illustrating a possible, highly simplified sequence of the presented procedure.

[0044] Figure 6 shows a schematic, highly simplified representation of a vehicle with one embodiment of the described arrangement. R. 415010

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[0046] Embodiments of the invention

[0047] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0048] 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.

[0049] Figure 1 illustrates in particular the specific problem that arises during driver monitoring when SAE L2 is switched on and interacts with the driver.

[0050] 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.

[0051] 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.

[0052] The procedure is implemented, for example, with a fail-safe steering system that has a KLA function (Keep Last Angle) as a preventative measure, e.g., implemented on a backup microcontroller. The system response in the event of a single-point error should be as follows: switching to the backup microcontroller, maintaining the last rotor position for at least 2.5 seconds, and R. 415010

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[0054] The driver is required to regain control of the vehicle. This applies specifically only in the case of a serious fault in the main microcontroller 102. Otherwise, "gentler" measures can also be initiated, see 254 in Figure 3. It should be noted that the reaction to a single-point fault depends on the fault itself.

[0055] Input signals, such as the requested state and rack position, should be guaranteed with sufficient safety integrity. A fault in the input signals cannot be detected by the steering system and should be addressed by the vehicle control unit with an appropriate ASIL integrity level.

[0056] 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.

[0057] The diagram shows a vehicle control system with a trajectory controller 202, which 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.

[0058] The transmission of the requested rack position 203 to the computing unit 214 is only required for asymmetric speed limits.

[0059] 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. R. 415010

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[0061] The steering motor torque 230 is input into a rack and pinion speed limiter 232, as are the rack and pinion speed limits 216. The speed limiter 232 outputs a signal "limited motor torque" 234 to a crossfader 240. Furthermore, block 214 outputs the rack and pinion speed limits 216 to a rack and pinion speed monitor 238.

[0062] 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.

[0063] A motor torque 270 in ASIL-D is output to a power stage 272, which in turn outputs a rack movement 274.

[0064] Figure 4 illustrates the presented procedure in a graph 300. Graph 300, whose abscissa 302 represents time and whose ordinate 304 represents the rack position, shows the progression of the rack position. On the ordinate 304 are plotted an initial or requested rack position 310 and a zero position 312. The vehicle, whose behavior is described here, operates according to SAE L2+, meaning the driver's hands are not initially on the steering handles.

[0065] A first curve 320 shows the initial position of the rack, i.e., the requested rack position. Then, at time h 322, an event 323 occurs, leading to a power steering fault or failure. The driver is then warned, for example, by means of a visual and / or audible signal. R. 415010

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[0067] After a debouncing period 324, the rack moves back towards the zero position 312 at time t2326, as illustrated by curve 328. A ramp 329 is clearly visible in curve 328. This continues until time ts 330, which also marks the end of a waiting period 331, during which the driver is expected to take control of the vehicle. Curve 332 further illustrates the movement of the rack if the described procedure is not carried out.

[0068] Figure 5 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 rack is moved towards the zero position. The zero position is the position in which the vehicle travels straight ahead. This return movement of the rack occurs over a period of time and ends when the driver regains control of the vehicle, i.e., when their hands are back on the steering handle and they are actively steering.

[0069] Figure 6 shows a purely schematic representation of a vehicle designated as reference numeral 500. The vehicle 500 has a power steering system 502, which in turn comprises a rack 504 and a steering handle 505. 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. 415010 - 10 - 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 where the direction of travel is specified via a provided requested trajectory, After detecting a fault in the power steering (502), the rack (504) is moved towards a zero position (312), the movement of the rack (504) towards the zero position (312) is aborted when the driver regains control of the vehicle (500) and an intervention is made via the steering handle (505).

2. Method according to claim 1, wherein the requested trajectory is provided by a trajectory controller (202).

3. Method according to claim 1 or 2, wherein, after detection of the fault, a warning signal is first given to the driver.

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

5. Method according to any one of claims 1 to 4, wherein the movement of the rack (504) towards the zero position (312) takes place after the expiry of a debounce period (324).

6. Method according to any one of claims 1 to 5, wherein the movement of the rack (505) towards the zero position (312) is such that it is completed by the end of a waiting period (331). R. 415010 - 11 - 7. Method according to any one of claims 1 to 6, wherein the movement of the rack (504) towards the zero position (312) is continuous.

8. Method according to claim 7, wherein the movement of the rack (505) towards the zero position (312) follows a ramp (329).

9. Arrangement for operating a power steering system (502) comprising 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 arrangement (506) comprises an evaluation unit (508) which is configured to carry out a method according to one of claims 1 to 8.

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