SYSTEM AND METHOD FOR DYNAMIC EXTENSION OF A STEERING RELATIONSHIP

Abstract

A steer-by-wire system includes a steering wheel actuator coupled to a steering column, a steering angle sensor coupled to the steering column and configured to measure steering column movement, a wheel actuator configured to engage the steering rod, and a controller in electrical communication with the steering wheel actuator, steering angle sensor, and wheel actuator. The controller is configured to identify movement of the steering wheel actuator, which is mechanically coupled to the steering column, using a steering angle sensor and to determine the steering wheel actuator's acceleration. The controller is also configured to determine the acceleration of the wheel actuator, which is configured to engage the steering rod, selectively changing a wheel angle and increasing the steering ratio of the steer-by-wire system when the wheel actuator's acceleration exceeds a predetermined threshold.

Description

BACKGROUND

[0001] The present disclosure relates to the steering of a vehicle and in particular to a steering system that dynamically increases a steering ratio in a steer-by-wire system.

[0002] Steer-by-wire systems are an alternative to mechanical steering linkages, which provide a direct mechanical connection found in many vehicles. Steer-by-wire systems use electronic controls and actuators to translate input from a driver at the steering wheel into an output that causes the steerable wheels to move to a desired driving angle. Mechanical steering systems rely on a direct mechanical connection between the steering wheel and the steerable wheels via a steering column, rod, and drive gear, or similar mechanisms. Mechanical steering systems may include a motor or hydraulic power assist to help the driver turn the steerable wheels. DESCRIPTION

[0003] This document discloses a steer-by-wire system. The system includes a steering wheel actuator coupled to a steering column, a steering angle sensor coupled to the steering column and configured to measure steering column movement, a wheel actuator configured to engage a steering rod, and a controller in electrical communication with the steering wheel actuator, the steering angle sensor, and the wheel actuator. The controller is configured to identify movement of a steering wheel actuator, mechanically coupled to the steering column, with a steering angle sensor and to determine the acceleration of the steering wheel actuator.The controller is also configured to determine the acceleration of a wheel actuator that is configured to engage the steering linkage to selectively change a wheel angle and increase the steering ratio of the steer-by-wire system when the acceleration of the wheel actuator exceeds a predetermined threshold.

[0004] In one aspect of the revelation, the control is configured to determine a speed of the steering wheel actuator and to hold the impeller actuator in a fixed position when the speed of the steering wheel actuator is zero.

[0005] In one aspect of the revelation, the control is configured to maintain a constant steering ratio of the steer-by-wire system when the acceleration of the steering wheel actuator is less than a predetermined threshold.

[0006] In one aspect of the revelation, the steering wheel actuator is configured to provide feedback torque through the steering column.

[0007] In one aspect of the revelation, the system includes a position sensor configured to determine the position of the steering rod, and the controller is configured to determine the acceleration of the wheel actuator using the steering rod position sensor.

[0008] In one aspect of the revelation, the control is configured to determine a speed of the impeller actuator with the position sensor and to increase a feedback torque to the steering column through the steering wheel actuator when the speed of the impeller actuator is above a predetermined threshold.

[0009] In one aspect of the revelation, the impeller actuator includes a drive unit configured to engage with the steering column via a gear drive.

[0010] In one aspect of the revelation, the control system is configured to selectively operate the drive unit to generate varying steering ratios.

[0011] This document discloses a method for operating a steer-by-wire system. The method includes identifying the movement of a steering wheel actuator mechanically coupled to a steering column with a steering angle sensor and determining the acceleration of the steering wheel actuator. The method also includes determining the acceleration of a wheel actuator configured to engage a steering rod and selectively change a wheel angle, thereby increasing the steering ratio of the steer-by-wire system when the acceleration of the wheel actuator exceeds a predetermined threshold.

[0012] In one aspect of the disclosure, the method involves determining the speed of the impeller actuator and increasing a feedback torque to the steering column by the steering wheel actuator when the speed of the impeller actuator exceeds a predetermined threshold.

[0013] In one aspect of the revelation, identifying a movement of the steering wheel actuator involves determining a speed of the steering wheel actuator and holding the impeller actuator in a fixed position when the speed of the steering wheel actuator is zero.

[0014] In one aspect of the disclosure, the method involves maintaining a constant steering ratio of the steer-by-wire system when the acceleration of the steering wheel actuator is less than a predetermined threshold.

[0015] In one aspect of the revelation, the steering wheel actuator is configured to provide feedback torque through the steering column.

[0016] In one aspect of the revelation, the wheel actuator is configured to drive the steering column with varying steering ratios.

[0017] This document discloses a vehicle. The vehicle includes a steering wheel actuator coupled to a steering column, a steering angle sensor coupled to the steering column and configured to measure movement of the steering column, a wheel actuator configured to engage a steering rod, and a controller in electrical communication with the steering wheel actuator, the steering angle sensor, and the wheel actuator. The controller is configured to identify movement of a steering wheel actuator, which is mechanically coupled to the steering column, with a steering angle sensor and to determine acceleration of the steering wheel actuator.The controller is also configured to determine the acceleration of a wheel actuator that is configured to engage the steering linkage to selectively change a wheel angle and increase the steering ratio of the steer-by-wire system when the acceleration of the wheel actuator exceeds a predetermined threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are included in and form part of this specification, illustrate implementations of the revelation and, together with the description, explain the principles of the revelation. Fig. Figure 1 schematically illustrates a vehicle that incorporates an exemplary steer-by-wire system. Fig. Figure 2 is a flowchart of a procedure for operating the exemplary steer-by-wire system from Fig. 1. Fig. Figure 3 is a graphical representation of changes in a steering ratio for the steer-by-wire system. DETAILED DESCRIPTION

[0019] Average professionals will recognize that terms such as "above," "below," "up," "down," "above," "below," "left," "right," etc., are used descriptively for the figures and do not represent limitations on the scope of disclosure as defined by the attached claims. Furthermore, the teachings herein may be described in terms of functional and / or logical block components and / or various processing steps.

[0020] Fig. Figure 1 illustrates an example of a vehicle 10 that includes a steering system 12, such as a steer-by-wire system. In the illustrated example, the vehicle 10 includes a body 14, which at least partially defines a passenger cabin, supported by a pair of rear wheels 16 and a pair of front wheels 18, which are steerable to generate a road angle for steering the vehicle 10 in a desired direction. The steering system 12 includes a steering wheel actuator (HWA) 22, which is mechanically connected to a steering wheel 20, such as a hand steering wheel, and a wheel actuator (RWA) 30, which is mechanically connected to a steering rod 36 for moving the front wheels 18 to different road angles.

[0021] The steering wheel 20 is connected to an upper steering column 24, such that turning the steering wheel 20 in a desired direction causes the upper steering column to rotate in the same direction and at the same speed. A steering angle sensor (SAS) 28 is mounted on the steering column 24 and monitors steering input from the steering wheel 20. In particular, the SAS 28 determines the position and rotational speed of the steering wheel 20. The position and rotational speed of the steering wheel 20, determined by the SAS 28, are communicated to an electronic control unit (ECU) 40, as discussed in more detail below.

[0022] In the illustrated example, the HWA 22 includes redundant drive units 23, each comprising a motor and a motor control unit, each communicating with a gear drive 25 mechanically connected to the upper steering column 24. When the ECU 40 receives position and yaw rate information from the SAS 28, the ECU 40 provides a feedback torque command to the HWA 22, which is received by at least one of the motor control units. The feedback torque command instructs the HWA 22 to apply a feedback torque to the steering column 24, which is felt by the driver manipulating the steering wheel 20. One feature of the HWA 22 is to provide the driver with feedback from the front wheels 18, similar to a mechanical steering system.

[0023] The steering system 12 also includes a wheel actuator (RA) 30 in electrical communication with the ECU 40. The RWA 30 engages with a steering rod 36 via a gear drive 32, which instructs the front wheels 18 to assume different track angles. In the illustrated example, the RWA 30 includes redundant drive units 31, each comprising a motor and a motor controller. Each of the motor and controller combinations is configured to receive command signals from the ECU 40 and drive the gear drive 32 to cause the steering rod 36 to move the front wheels 18 to the desired track angle. The steering rod 36 is connected to a steering knuckle 39 at each of the front wheels 18 by a pair of tie rods 38. The front wheels 18 are rotatably connected to the steering knuckle 40 by a wheel bearing hub. A lateral movement of the tie rods 38 causes the front wheels 18 to assume a desired road angle.The lateral position of the steering rod 36 is monitored by a rod position sensor 34, which communicates electrically with the ECU 40 to provide the ECU 40 with information regarding the position and movement, such as acceleration and speed, of the steering rod 36. Accordingly, the ECU 40 provides suitable signals to the RWA 30 to change the position of the steering rod 36, and the rod position sensor 34 monitors the position of the steering rod 36 and communicates this information to the ECU 40 for control purposes.

[0024] In this disclosure, the ECU 40 may be equipped with one or more processors (P), e.g., logic circuits, combinational logic circuit(s), application-specific integrated circuit(s) (ASIC), electronic circuit(s), central processing unit(s), semiconductor IC devices, etc., as well as input / output (I / O) circuitry, suitable signal conditioning and buffering circuits, and other components, such as a high-speed clock generator. The ECU 40 also includes an associated non-volatile, computer-readable storage medium, i.e., memory (M), including read-only memory, programmable read-only memory, direct access memory, a hard disk, etc., whether resident, remote, or a combination of both.

[0025] Fig. Figure 2 illustrates a flowchart of an exemplary procedure 100 for operating the steering system 12. Fig. 1. Procedure 100 begins at block 102 ("Start"). From block 102, procedure 100 proceeds to block 104.

[0026] At block 104 (“HWA speed = 0”), procedure 100 determines a rotational speed of the HWA 22. Procedure 100 can use the SAS 28 in conjunction with the ECU 40 to determine the rotational speed of the HWA 22 at a specific time. If the ECU 40 determines that the speed of the HWA 22 is zero, procedure 100 proceeds to block 106 (“Hold RWA position”).

[0027] At block 106 of procedure 100, procedure 100 instructs the RWA 30 via the ECU 40 to maintain a constant position to prevent changes in the track angle of the front wheels 18. From block 106, procedure 100 returns to block 104 to continue monitoring the speed of the HWA 22. When the speed of the HWA 22 is no longer zero, procedure 100 proceeds to block 108.

[0028] At block 108 (“HWA acceleration above threshold”), procedure 100 determines the acceleration of HWA 22 using SAS 28 in conjunction with ECU 40. Procedure 100 then compares this determined acceleration of HWA 22 to a predetermined threshold. If the acceleration of HWA 22 determined at block 108 by SAS 28 is less than the predetermined threshold, procedure 100 proceeds to block 110.

[0029] At block 110 (“Maintain steering ratio”), procedure 100 maintains a predetermined steering ratio for steering system 12. The steering ratio for steering system 12 defines a relationship between degrees of steering wheel rotation 20 and degrees of road angle for the front wheels 18. If the acceleration of the HWA 22 at block 108 is greater than the predetermined threshold, procedure 100 switches to block 112.

[0030] At block 112 (“RWA acceleration above threshold?”), procedure 100 determines the acceleration of the RWA 30. In one example, the acceleration of the RWA 30 is measured by the rod position sensor 34 to determine the acceleration of the steering rod 36 in a lateral direction. If the acceleration measured for the RWA 30 is less than a predetermined threshold, procedure 100 proceeds to block 110 to maintain the steering ratio and then continues to monitor the movement of the HWA 22 at block 104. If the acceleration measured for the RWA 30 is greater than the predetermined threshold, procedure 100 proceeds to block 114.

[0031] In block 114 (“Increase steering ratio”), procedure 100 increases the steering ratio for steering system 12 to slow down the reaction of the RWA 30 relative to the HWA 22. Increasing the steering ratio for steering system 12 results in a reduced track angle for the front wheels 18 at a given steering wheel 20 rotation for steering system 12. A characteristic of dynamically increasing the steering ratio for steering system 12 is a reduction in rapid changes of direction for vehicle 10, which can cause discomfort for the occupants. Accordingly, increasing the steering ratio under these circumstances provides a smoother driving experience for the occupants of vehicle 10.

[0032] Fig.Figure 3 provides a graphical representation 200 of the dynamic increase of the steering ratio while the vehicle is being driven. Specifically, the graphical representation includes a first graphical representation 202 of the steering ratio for the steering system 12 over time, a second graphical representation 204 of the HWA acceleration 210 over time, and a third graphical representation 206 of the RWA acceleration 212 over time. As shown in graphical representation 202, the steering ratio SR remains at a nominal value 214 until it is increased to a dynamic value 208. The transition to the dynamic value 208 corresponds to a time at which the HWA acceleration and the RWA acceleration each exceed a predetermined threshold value 216 and 218, respectively. From block 114, the procedure 100 transitions to block 116.

[0033] At block 116, procedure 100 determines the speed of the RWA 30. In one example, the speed of the RWA 30 is measured by the rod position sensor 34 by determining the speed of the steering rod 36 in a lateral direction. If the speed of the RWA 30 is less than a predetermined threshold, procedure 100 returns to block 110 and maintains the increased steering ratio from block 114. Procedure 100 then returns to block 104 to continue monitoring the movement of the HWA 22. If the speed of the RWA 30 is greater than the predetermined threshold, procedure 100 proceeds to block 118.

[0034] At block 118 (“Increase torque”), procedure 100 increases the torque feedback to the steering wheel 20 through the steering column 24 by using the HWA 22. Increasing the torque feedback, which is felt by the driver in the steering wheel 20, reduces the speed and acceleration for both the HWA 22 and the RWA 30. With the torque feedback increased at block 118, procedure 100 returns to block 108 to continue monitoring the movement of the steering system 12.

[0035] The terms "a" and "an" do not denote a limitation of the set, but instead indicate the presence of at least one of the referenced elements. The term "or" means "and / or" unless clearly indicated otherwise by the context. Reference throughout the specification to "an aspect" means that a particular element (e.g., feature, structure, step, or property) described in connection with that aspect is contained in at least one aspect described herein and may or may not be present in other aspects. Furthermore, it is understood that the described elements can be combined appropriately across the various aspects.

[0036] While the above disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various modifications can be made and equivalents can be replaced by elements thereof without altering its scope. Furthermore, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without altering its scope. Therefore, it is intended that the present disclosure is not limited to the specific embodiments disclosed, but includes embodiments that fall within its scope.

Claims

[1] Steer-by-wire system, including: a steering wheel actuator that is coupled to a steering column; a steering angle sensor that is coupled to the steering column and configured to measure movement of the steering column; a wheel actuator configured to engage with a steering column; and a controller in electrical communication with the steering wheel actuator, the steering angle sensor and the wheel actuator, wherein the controller is configured to: to identify the movement of a steering wheel actuator mechanically coupled to the steering column with a steering angle sensor, wherein the steering angle sensor is configured to rotate with the steering column; to determine the acceleration of the steering wheel actuator; to determine the acceleration of a wheel actuator configured to engage the steering linkage to selectively change a wheel angle; and to increase the steering ratio of the steer-by-wire system when the acceleration of the impeller actuator exceeds a predetermined threshold. [2] System according to claim 1, wherein the controller is configured to determine a speed of the steering wheel actuator and to hold the wheel actuator in a fixed position when the speed of the steering wheel actuator is zero. [3] System according to claim 1, wherein the control is configured to maintain a constant steering ratio of the steer-by-wire system when the acceleration of the steering wheel actuator is less than a predetermined threshold. [4] System according to claim 1, wherein the steering wheel actuator is configured to provide a feedback torque through the steering column. [5] System according to claim 1, comprising a position sensor configured to determine a position of the steering rod, and wherein the controller is configured to determine the acceleration of the wheel actuator using the steering rod position sensor. [6] System according to claim 5, wherein the control is configured to determine a speed of the impeller actuator with the position sensor and to increase a feedback torque to the steering column through the steering wheel actuator when the speed of the impeller actuator is above a predetermined threshold. [7] System according to claim 1, wherein the wheel actuator includes a drive unit configured to engage the steering rod via a gear drive. [8] System according to claim 7, wherein the control is configured to operate the drive unit selectively to produce varying steering ratios. [9] Method for operating a steer-by-wire system, the method comprising: Identifying a movement of a steering wheel actuator mechanically coupled to a steering column with a steering angle sensor, wherein the steering angle sensor is configured to rotate with the steering column; Determining the acceleration of the steering wheel actuator; Determining the acceleration of a wheel actuator configured to engage a steering rod and selectively change a wheel angle; and Increasing the steering ratio of the steer-by-wire system when the acceleration of the impeller actuator exceeds a predetermined threshold. [10] Method according to claim 9, comprising determining a speed of the impeller actuator and increasing a feedback torque to the steering column by the steering wheel actuator when the speed of the impeller actuator is above a predetermined threshold.

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