Rack-limiting condition detection and the corresponding steering wheel torque feedback for steer by wire steering systems

Technical solutions are described herein for steer-by-wire (SBW) steering systems to detect a rack-limiting condition and generate feedback signal that can provide responsive handwheel torque for a driver. According to one or more embodiments the steer-by-wire steering system includes a processor that receives input signals comprising a handwheel velocity signal and a vehicle speed signal. The processor determines a simulated left end stop position of a rack based on the input signals, and a simulated right end stop position of a rack based on the input signals. The processor compares a rack position with the simulated left end stop position and the simulated right end stop position. The processor generates a feedback signal based on a determination that the rack position is not within a range bound by the left end stop position and the right end stop position.

BACKGROUND

Steer by wire (SBW) steering systems do not have a direct mechanical connection between the human driver and the steerable road wheels, rather input from the human driver is conveyed to the road wheels using one or more electrical signals that cause torque to be generated and applied at the road wheels. The driver interacts with a handwheel actuator (HWA), and the road wheels are steered by a road wheel actuator (RWA). These two systems are only linked electrically (by wires).

SUMMARY

Technical solutions are described herein for steer-by-wire (SBW) steering systems to detect a rack-limiting condition and generate responsive handwheel torque for a driver.

According to one or more embodiments, a steer-by-wire steering system detects a rack-limiting condition. The steer-by-wire steering system includes a processor that receives input signals comprising a handwheel velocity signal and a vehicle speed signal. The processor determines a simulated left end stop position of a rack based on the input signals, and a simulated right end stop position of a rack based on the input signals. The processor compares a rack position with the simulated left end stop position and the simulated right end stop position. The processor generates a feedback signal based on a determination that the rack position is not within a range bound by the left end stop position and the right end stop position.

According to one or more embodiments, a method to detect a rack-limiting condition includes receiving input signals comprising a handwheel velocity signal and a vehicle speed signal. The method further includes determining a simulated left end stop position of a rack based on the input signals. The method further includes determining a simulated right end stop position of a rack based on the input signals. The method further includes comparing a rack position with the simulated left end stop position and the simulated right end stop position. The method further includes generating a feedback signal based on a determination that the rack position is not within a range bound by the left end stop position and the right end stop position.

A computer program product comprising a computer readable storage device having stored therein one or more computer executable instructions, which when executed by a processor perform a method to detect a rack-limiting condition. The method includes receiving input signals comprising a handwheel velocity signal and a vehicle speed signal. The method further includes determining a simulated left end stop position of a rack based on the input signals. The method further includes determining a simulated right end stop position of a rack based on the input signals. The method further includes comparing a rack position with the simulated left end stop position and the simulated right end stop position. The method further includes generating a feedback signal based on a determination that the rack position is not within a range bound by the left end stop position and the right end stop position.

DETAILED DESCRIPTION

As used herein the terms module and sub-module refer to one or more processing circuits such as an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. As can be appreciated, the sub-modules described below can be combined and/or further partitioned.

Described herein are several embodiments of steering systems, such as steer-by-wire (SBW) steering systems, that provide curb-condition detection.

Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, a steer by wire steering (SBW) system40in a vehicle100is depicted inFIG. 1. It will be appreciated that the SBW system40shown and described can be used in an autonomous or semi-autonomous vehicle or in a more conventional vehicle. The SBW system40includes a handwheel actuator (HWA)10and a roadwheel actuator (RWA)20.

The HWA10includes one or more mechanical components12, such as a handwheel (steering wheel), a steering column, a motor/inverter attached to the steering column either through a gear mechanism or a direct drive system. The HWA10further includes a microcontroller14that controls the operation of the mechanical components12. The microcontroller14receives and/or generates torque via the one or more mechanical components12.

The RWA includes one or more mechanical components22, such as a steering rack and/or pinion coupled to a motor/inverter through a ball-nut/ball-screw (gear) arrangement, and the rack is connected to the vehicle roadwheels/tires through tie-rods. The RWA20includes a microcontroller24that controls the operation of the mechanical components22. The microcontroller24receives and/or generates torque via the one or more mechanical components22.

The microcontrollers14and24are coupled through electrical connections that allow signals to be transmitted/received. As referred to herein, a controller can include a combination of the HWA controller14and the RWA controller24, or any one of the specific microcontrollers.

In one or more examples, the controllers14and24of the SBW system40communicate with each other through CAN interface (or other similar digital communication protocols). Guidance of the vehicle100that is fitted with the SBW system40is performed by use of the steering gear, with an input shaft that is rotated by the RWA20, such as a servo actuator. The RWA20receives an electronic communication signal of rotation of the steering wheel by the driver. A driver controls the steering wheel to directionally control the vehicle100. The angle from HWA10is sent to the RWA20which performs position control to control rack travel to guide the roadwheel. However, due to the lack of mechanical connection between the steering wheel and the road wheels, the driver is not provided with a feel for the road without torque feedback (unlike the case in an EPS as described earlier).

In one or more examples, the HWA10that is coupled to the steering column and steering wheel simulates the driver's feel of the road. The HWA10may apply tactile feedback in the form of torque to the steering wheel. The HWA10receives a rack force signal from the RWA20to generate an appropriate torque feel for the driver. Alternatively, the handwheel angle and vehicle speed can also be used to generate desired torque feel to the driver.

It will be appreciated that the steer-by-wire steering system40that is shown and described can be used in an autonomous or semi-autonomous vehicle or in a more conventional vehicle. For example, the controllers14and24may also be associated with an autonomous or semi-autonomous vehicle utilizing an advanced driver assistance system (“ADAS”)27. The ADAS system27may utilize a navigation system that enables the vehicle100and its passengers to drive portal-to-portal without ever having the operator steer the vehicle100. When the ADAS system27is activated, the steering wheel12is not required for control of the vehicle100, and therefore, rotation of the steering wheel12is not required during the autonomous driving mode. In one or more examples that include the ADAS system27, in a non-active mode of the ADAS system27, the actuators10and20receive an electronic communication signal of rotation of the steering wheel12by the driver/operator of the vehicle100. The ADAS system27is activated when an autonomous vehicle driving condition is desired, thereby deactivating directional control of the road wheels by the steering wheel12. The driver is able to switch between the autonomous vehicle driving condition and a non-autonomous vehicle driving condition.

FIG. 2depicts a block diagram of the HWA according to one or more embodiments. The non-autonomous vehicle driving condition (non-active mode of ADAS system27, if ADAS system27is included) includes a driver controlling the steering wheel12to directionally control the vehicle100. As noted above, in a non-active mode of the ADAS system27, the HWA10receives an electronic communication signal of rotation of the steering wheel14by the driver. However, due to the lack of mechanical connection between the steering wheel12and the road wheels, the driver is not provided with a feel for the road without torque feedback. In one or more examples, the HWA10includes a torque system200to simulate torque for the driver. The torque system200may include a servo actuator coupled to a steering column16and the steering wheel12to simulate the driver's feel of the road. The torque system200may apply tactile feedback in the form of torque to the steering wheel12and/or the steering column16. It should be noted that in one or more examples, the torque feedback system200may provide the tactile feedback using any other components in lieu of another servo actuator coupled to the steering column16and steering wheel12to provide tactile feedback in the form of torque to the steering wheel12to simulate the driver's feel of the road.

Aspects of embodiments described herein may be performed by any suitable control system and/or processing device, such as the controllers14and24. In one embodiment, the controllers14and24may be an electronic control unit (ECU). The vehicle100can include additional ECUs. The controllers14and24receive information from the other ECUs, such as a vehicle speed signal, one or more sensor information signals, and various other information electronic signals. As described earlier, there are multiple communication methods designed for inter-micro communication, such as the protocols SCI, CAN, and MLI, among others. Each protocol may satisfy a portion of the safety aspects of data handling, but does not inherently ensure that all safety aspects are covered.

When using SBW, the torque supplied by the HWA motor is controlled to a Reference Torque (Tref). This reference torque is then compared to the actual torque measured at the handwheel (Tbar torque). The error between these two generates error, and a control loop is used to manage the torque error. The control is sometimes referred to as closed-loop torque control.

A technical challenge exists when the vehicle100is in a condition where the rack22cannot physically move due to either its mechanical limits, or environmental restrictions (for example, in a ditch, a rut, at a curb, or the like) or system capacity restrictions (for example, rack motor can be in a degraded state where its output capacity is reduced). In such cases, the normal steering feel algorithms cannot detect these conditions, and as a result the HWA10cannot provide an adequate amount of torque (typically large amount of torque and beyond a torque sensor sensing range) to represent, to the driver, the limited situation the rack is in. However, it is critical to inform the driver of these conditions so that the driver can take appropriate action. It is also very important to provide adequate torque feedback to prevent the driver from moving the handwheel12in a direction that the rack22cannot follow. The latter can cause the handwheel12and roadwheel (or rack22) to be out of synchronization which can create other problems. Accordingly a comprehensive function is needed to allow the detection of all situations where rack motion is restricted and provide appropriate feedback to the driver under those circumstances. The technical solution described herein address such technical challenges.

FIG. 3depicts a block diagram of rack limiting detection and feedback according to one or more embodiments. The detection and feedback are depicted using five function blocks: rack limiting detection threshold generation310, simulated end stop adjustment320, handwheel simulated end stop function330, SBW vehicle rack diagnostics340, and autonomous vehicle rack diagnostics/path planning350. It should be noted that the depicted blocks are exemplary and that in other examples, the detection and feedback can be represented using different blocks and/or additional and fewer blocks.

The SBW vehicle rack diagnostics340is responsible for dynamically determining a fault condition with the rack (or other components) of the SBW system40. For example, if the one or more components of the SBW system40are not operating within predetermined thresholds/ranges that are associated with the respective components, the SBW vehicle rack diagnostics340raises an error flag that can cause the SBW system40to notify the driver and/or prevent any further operation of the SBW system40. In one or more examples, if the vehicle100is equipped with an ADAS27, the error flag can cause the ADAS27to maneuver the vehicle100to a safe stop, to a service station, or perform any other maneuver.

In a similar manner, the autonomous vehicle rack diagnostics/path planning350is responsible for dynamically determining a fault condition with the rack (or other components) of the vehicle100. For example, if the one or more components of the vehicle100are not operating within predetermined thresholds/ranges that are associated with the respective components, the autonomous vehicle rack diagnostics/path planning350raises an error flag that can cause the vehicle100to notify the driver and/or prevent any further operation of the vehicle100. In one or more examples, the error flag can cause the ADAS27to maneuver the vehicle100to a safe stop, to a service station, or perform any other maneuver.

The rack limiting detection threshold generation310, takes vehicle speed and handwheel velocity as input and calculates a rack limiting detection threshold.FIG. 4depicts an example of how the rack limiting detection threshold can be calculated based on the two inputs according to one or more embodiments. As can be seen the rack limiting detection threshold varies dynamically as the vehicle speed changes.

Referring toFIG. 3, the second block, simulated end stop adjustment320, takes the calculated rack limiting detection threshold as well as a left rack mechanical end stop and a right rack mechanical end stop and calculates left and right simulated end stop positions. In one or more examples, the calculation is performed using following expressions. However, in other examples, the calculation can vary without deviating from the innovative concepts of the technical solutions described herein.
Simulated left end stop position=max(rack position−rack limiting detection threshold, left mechanical rack limit); and
Simulated right end stop position=min(rack position+rack limiting detection threshold, right mechanical rack limit).

The output of the simulated end stop adjustment320determines the state of the rack movement and relays this to the SBW vehicle rack diagnostics340if the vehicle100is a SBW-equipped vehicle. Alternatively, or in addition, the simulated end stop adjustment320conveys the output to the autonomous vehicle rack diagnostics/path planning350if the vehicle100is an autonomous vehicle. In the case that the vehicle100is a SBW equipped autonomous vehicle, both blocks340and350can receive the output from the simulated end stop adjustment320. The left rack mechanical end stop and the right rack mechanical end stop are predetermined values representing a physical limit of the movement of the rack.

Finally, the HW simulated end stop function330takes handwheel position, handwheel velocity, the left and right simulated end stop positions and computes an appropriate amount of notification torque (typically >10 Nm) to alert the driver of the circumstances and prevent the driver from creating out of synchronization condition between the handwheel12and the roadwheel. This function is performed in a SBW-equipped vehicle. This function is implemented by a position control algorithm as follows: if handwheel position is greater than (to the right of) right simulated end stop positions, activate position control algorithm to return handwheel12to the right simulated end stop position. Similarly, if handwheel position is less than (to the left of) left simulated end stop positions, also activate the position control algorithm to return the handwheel12to the left simulated end stop position. If the handwheel12is between left and right simulated end stop positions, then the handwheel simulated end stop function330is deactivated and normal steering feel function takes over to facilitate the torque system200to provide the driver normal steering feel.

The use of a position control algorithm rather than using the torque system200in handwheel simulated end stop function330allows the typical torque sensing limit of 10 Nm to be exceeded. Accordingly, an adequate amount of torque feedback can be provided to the driver for rack limiting feedback, where the adequate amount of torque is not limited by the torque sensing limit, rather by a torque generation limit of the HWA10. Typically, the torque generation limit of the HWA10(e.g. 65 Nm) is larger than the torque sensing limit (10 Nm). Accordingly, the technical solutions described herein facilitate the SBW40to provide a larger torque than before, where the larger torque can be noticed by the driver, and accordingly, causing a notification to the driver.

FIG. 5shows an example operation of the rack limiting condition detection and feedback according to an example scenario. InFIG. 5, “normal” steering feedback is provided to the driver when handwheel position is within the dashed lines, and otherwise the notification torque according to the rack limiting detection and feedback described herein is provided. Here, “normal” steering feedback is the simulated torque feedback according to road surface when the road wheel is not stuck or prevented from movements.

It can be seen fromFIG. 5that simulated end stop positions form a narrow band510around the actual rack position with the width of the band510being the detection threshold that was computed. When the band510meets the rack mechanical limit, the band510is then limited by the mechanical limit values (520). When rack is limited, rack cannot follow the handwheel12position, causing the handwheel position to go beyond the band510. When this happens, rack limiting is detected, and corresponding amount of feedback is provided by generating the notification torque to be provided at the handwheel12by using the simulated end stop330function described above.

FIG. 6shows another an example operation of the rack limiting condition detection and feedback according to an example scenario. In this example scenario, the rack is limited before the mechanical limit is reached. As can be seen, where rack is not limited, the rack position follows handwheel position based on the closed loop rack position tracking. In this case, handwheel position is always located between the simulated left and right end stop positions where the normal steering feel is provided using the torque system200. Where the rack is limited, i.e. the rack cannot follow the handwheel position, it causes the handwheel position to go beyond the simulated right end stop position. The segment of handwheel position curve610inFIG. 6represents the detection of rack limiting condition in which the corresponding amount of notification torque is provided to the driver as feedback.

FIG. 7depicts a flowchart for rack-limiting condition detection and the corresponding steering wheel torque feedback for SBW systems according to one or more embodiments. The depicted method700includes receiving, by a controller of the SBW system40, a handwheel velocity and a vehicle speed signal (710). The method700further includes determining, using the input values, a rack limiting detection threshold (720). The rack limiting detection threshold is further used for computing, at runtime, simulated end stop positions for the rack (730). The simulated end stop positions are computed for a left and a right movement of the rack. In one or more examples, additional simulated end stop positions can also be computed. The simulated end stop positions are further limited using predetermined mechanical stop positions of the rack (740).

The method further includes comparing the rack position with the simulated end stop positions that are computed (750). If the rack position is within a band formed by the simulated end stop positions, the RWA20provides “normal” feedback according to road surface, such as based on a coefficient of friction of the road surface (760). Such feedback is limited by the torque sensing capabilities, such as within 10 Nm (first predetermined limit).

Alternatively, if the rack position exceeds the band formed by the simulated end stop positions, the RWA20generates and provides a feedback signal (770). The feedback signal can include a torque command for the HWA10to generate at the handwheel12. For example, the torque command can be larger torque (compared to the normal feedback). The torque command is not limited by the torque sensing capabilities, rather by the torque generation limit of the HWA10, such as 65 Nm (second predetermined limit). The torque command can inhibit movement of the handwheel12by the driver, accordingly, preventing the handwheel12to be at a position that is unsynchronized with the road wheels that are stuck.

In one or more examples, the feedback signal can include a notification to the ADAS27to adjust a maneuver of the vehicle100. For example, the ADAS27can stop the vehicle100and/or stop requesting the vehicle100to turn in the direction in which the curb/rut is detected. The ADAS27can further update a path planned for the vehicle100based on the feedback. It will be appreciated that, as used and defined herein, the term “curb” may refer to any type of environmental obstruction encountered by one or more roadwheels that would cause a limit of rack travel and is not to be interpreted as only a physical road curb. In non-limited examples, the term “curb” as used herein may refer to any environmental obstruction such as a physical curb, a rut, a ramp, a raised or depressed sewer grate, a small ditch or hump, etc.

The technical solutions described herein accordingly facilitate an SBW to detect the rack-limiting conditions. Further, the technical solutions described herein ensure to not falsely set diagnostics related to tracking errors between the HWA and the RWA. If the rack-limiting condition is not properly detected, the driver may continue turning the wheel (when limited to a predetermined value) and the position tracking error may increase and potentially falsely trigger an error when it is not a system failure, rather an environmental condition limiting the SBW system from performing as expected. Providing the additional HWA torque (up to a predetermined maximum HWA maximum value) reduces the chances of such false tracking errors in the rack-limiting conditions, and additionally provide a more robust input to diagnostics within the SBW system.

Aspects of the present technical solutions are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the technical solutions. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

It will also be appreciated that any module, unit, component, server, computer, terminal or device exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Such computer storage media may be part of the device or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media.

While the technical solutions are described in detail in connection with only a limited number of embodiments, it should be readily understood that the technical solutions are not limited to such disclosed embodiments. Rather, the technical solutions can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the technical solutions. Additionally, while various embodiments of the technical solutions have been described, it is to be understood that aspects of the technical solutions may include only some of the described embodiments. Accordingly, the technical solutions are not to be seen as limited by the foregoing description.