Method for operating a power steering system

Abstract

Method for operating a power steering system comprising a rack that is driven for steering purposes, wherein the method is carried out upon occurrence of a fault in the power steering system, a rack position requested for steering is specified and compared with an actual rack position so that a rack position deviation is determined, the rack velocity is monitored, for which purpose said rack velocity is detected, the detected rack velocity is compared with at least one limit value, and the at least one limit value is established depending on the direction in which the rack is moving.

Description

[0001] R. 415011

[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. 415011.

[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 9 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 rack and pinion driven for steering. The method is executed particularly when a fault occurs in the power steering system. A rack position requested for steering is specified and compared with the actual rack position to determine any rack position deviation. The rack speed is then monitored by recording it, compared to a limit value, and the limit value is set depending on the direction of rack movement.

[0018] In this method, a first limit value can be set for the case that the rack moves towards the requested rack position, and a second limit value can be set for the case that the rack moves away from the requested rack position, with the first limit value being higher in magnitude than the second limit value, resulting in asymmetric monitoring.

[0019] In another embodiment, a factor R is used depending on the vehicle speed and the rack position deviation. 415011

[0020] - 3 -

[0021] The limit value is determined using this method. Please refer to the table below.

[0022] The method can also include a limitation on the control of the rack. This can also be done asymmetrically.

[0023] When the limit value is reached, at least one countermeasure can be initiated. For example, the torque of the motor driving the rack can be limited and / or a warning can be issued to the driver.

[0024] In this procedure, the driver is permitted to take their hands off the steering wheel. This falls under SAE Level 2+. The aim is to ensure that, in the event of an error, the deviation from the trajectory does not exceed a certain degree within the driver's reaction time. Safety limits can be specified by the customer or driver.

[0025] The presented arrangement serves to carry out the described procedure and is equipped with an evaluation unit for this purpose. The arrangement and / or the evaluation unit are implemented in hardware and / or software. Furthermore, the arrangement can be integrated into a vehicle's control unit or be designed as such a control unit. This control unit, in turn, is, for example, a steering control unit.

[0026] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0027] 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.

[0028] Brief description of the drawings

[0029] Figure 1 shows a vehicle at the vehicle level in a block diagram. R. 415011

[0030] - 4 -

[0031] Figure 2 shows a steering control unit in a block diagram.

[0032] Figure 3 shows an embodiment of the presented safety mechanism in a block diagram.

[0033] Figure 4 shows in a diagram the mode of operation of the presented method.

[0034] Figure 5 shows different use cases.

[0035] Figure 6 shows a flowchart illustrating a possible, highly simplified sequence of the presented procedure.

[0036] Figure 7 shows a schematic, highly simplified representation of a vehicle with one embodiment of the described arrangement.

[0037] Figure 8 shows different scenarios in a graph.

[0038] Embodiments of the invention

[0039] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0040] 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.

[0041] Figure 1 illustrates in particular the specific problem that arises during driver monitoring when SAE L2 is switched on and interacts with the driver R. 415011

[0042] - 5 -

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The transmission of the requested rack position 203 to the computing unit 214 is only required for asymmetric speed limits.

[0048] 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. 415011

[0049] - 6 -

[0050] 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.

[0051] 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.

[0052] A motor torque 270 in ASIL-D is output to a power stage 272, which in turn outputs a rack movement 274.

[0053] Block 214 is of particular importance, as it replaces or eliminates the previous symmetrical rack speed limits with asymmetrical rack speed limits.

[0054] Block 214 introduces asymmetrical rack speed limits. This is intended to prevent the rack in the steering system from making an erroneous movement in the wrong direction. Incorrect direction means movement away from the requested rack position. Correct direction means movement towards the requested rack position. This means that input signals—requested state and requested rack position—should be provided with sufficient safety integrity (ASIL-D). Previously, erroneous rack movement was permitted in both directions, limiting steering performance in the desired direction. R. 415011

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[0056] Figure 4 illustrates this using trajectories. The illustration shows a requested rack position 300, a first deviating trajectory 302, and a second deviating trajectory 304. A double arrow 310 indicates the incorrect direction for both deviating trajectories 302 and 304.

[0057] Figure 5 shows a first use case 400 on the left and a second use case 402 on the right. The illustration shows an actual rack position 410 and a requested rack position 412 in the first use case 400. A first arrow 420 indicates an incorrect direction, where a low rack speed is desired. A second arrow 422 indicates a correct direction, where a high rack speed is possible.

[0058] In the second use case 402, the actual rack position is 430 and the requested rack position is 432. A first arrow 440 indicates an incorrect direction, where a low rack speed is desired. A second arrow 442 indicates a correct direction, where a high rack speed is possible.

[0059] In this context, asymmetrical means that different rack speed limits or thresholds are specified or defined for deviations. One goal is to identify the current rack speed as it approaches the requested rack position and to assign a higher permissible rack speed to it.

[0060] The procedure may include the calculation of a factor.

[0061] This is discussed in more detail in the table below.

[0062]

[0063] Table 1 R. 415011

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[0065] The first row lists vehicle speeds. The column to the right lists rack position deviations. The table shows associated factors, where a factor of 1 means the limits are symmetrical; that is, with a rack position deviation of 0, the limits are symmetrical regardless of vehicle speed.

[0066] 0 < factor < 1 means that the rack speed is limited in the wrong direction.

[0067] A factor < 0 means that a rack speed in the correct direction is ensured.

[0068] Figure 6 shows a highly simplified flowchart of the presented procedure. In a first step 450, a vehicle equipped with power steering begins to travel. In step 452, a fault occurs. Ideally within the driver's reaction time, the movement or speed of the rack is then monitored in step 454. For this purpose, a speed limit is calculated in step 456, taking into account whether the rack is moving towards or away from a requested rack position.

[0069] Figure 7 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 includes a rack and pinion 504. Furthermore, an arrangement 506 is provided, which is configured to carry out the presented method and for this purpose has an evaluation unit 508.

[0070] Figure 8 shows different scenarios in a graph 600 in conjunction with the two tables below. Scenarios 1 to 6 are shown. A first curve 602 illustrates a symmetrical rack speed limitation in mm / s at 30 kph. A second curve 604 shows a maximum permissible positive rack speed in mm / s. R. 415011

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[0072] A third curve, 606, shows a maximum permissible negative rack speed in mm / s. R. 415011

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[0074] Example of the positive side of the rack

[0075] Example of asymmetric rack speed

[0076]

[0077] Table 2 R. 415011

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[0079] Negative rack side

[0080] Example of negative rack speed

[0081]

[0082] Table 3

[0083] In both tables, dir (direction) denotes a direction.

Claims

R. 415011 - 12 - Claims 1. Method for operating a power steering system (502) comprising a rack (504) which is driven for steering, wherein the procedure is carried out when a fault occurs in the power steering (502), a rack position (203, 300, 412, 432) requested for steering is specified, which is compared with an actual rack position (204, 410, 430) so that a rack position deviation (208) is determined, Monitoring of the rack speed is carried out, for which purpose it is recorded, the recorded rack speed is compared with at least one limit value (216), and which at least one limit value (216) is set depending on the direction in which the rack (504) moves.

2. Method according to claim 1, wherein a first limit value is set for the case that the rack (504) moves towards the requested rack position (203, 300, 412, 432), and a second limit value is set for the case that the rack (504) moves away from the requested rack position (203, 300, 412, 432), wherein the first limit value is higher in magnitude than the second limit value, resulting in asymmetric monitoring.

3. Method according to claim 1 or 2, wherein depending on the vehicle speed and the rack position deviation (208) R. 415011 - 13 - a factor is determined with which at least one limit value (216) is determined.

4. Method according to one of claims 1 to 3, wherein an additional limitation is imposed on the control of the rack (504).

5. Method according to any one of claims 1 to 4, wherein at least one countermeasure is initiated upon reaching at least one limit value (216).

6. Method according to claim 5, wherein, upon reaching at least one limit value (216), a limitation of the torque of the motor (110) driving the rack (504) is carried out.

7. Method according to claim 5 or 6, wherein a warning is issued to the driver (22) when at least one limit value (216) is reached.

8. Method according to claim 7, wherein an optical and / or acoustic warning message is issued when at least one limit value (216) is reached.

9. Arrangement for operating a power steering system in a vehicle (500) with an evaluation unit (508) which is configured to carry out a method according to one of claims 1 to 8.

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