STEER-BY-WIRE DRIFT COMPENSATION

Abstract

Steer-by-wire system (119), wherein the system (119) comprises: a control unit (144) which, in response to a handwheel orientation (166) defined by an angular position (160) of a handwheel (122), which has a handwheel orientation offset value (162) corresponding to a substantially straight desired direction of movement (112) with respect to a predetermined handwheel zero value (164), and at least a yaw rate (306) associated with a rate of change of a yaw position about a yaw axis (115) that is less than a predetermined yaw rate threshold value (320), or a lateral acceleration that is less than a predetermined lateral acceleration threshold value, can be operated to actuate a road wheel actuator (142) for aligning road wheels (104) such that a position command (212) to the road wheel actuator (142) based on the handwheel orientation (166) corresponds to the handwheel orientation offset value (162) in the opposite direction corresponds,to reduce the difference between the handwheel orientation offset value (162) and the predetermined handwheel zero value (164) when the road wheels (104) are angled / turned.

Description

[0001] This disclosure relates to steer-by-wire systems and a control unit program product of a steer-by-wire system.

[0002] Steer-by-wire systems mechanically separate operator interfaces, such as a steering wheel or handwheel, from wheel-steering mechanisms. This means the steering shaft or steering column can be partially or completely removed, and operator steering commands are sent to motorized wheel-steering systems. These road wheel-steering systems or road wheel actuators can translate handwheel rotation into lateral movement of the road wheel. Strong winds, tire pressure differences, and other driving conditions may require operators to rotate the handwheel to an offset angle to maintain straight vehicle movement.

[0003] DE 11 2010 005 308 B4 discloses a steering control device capable of adapting reference points of a plurality of movements used for a steering operation in a steering actuation unit with high precision. DE 10 2017 207 229 A1 discloses a method for aligning a steering wheel. For this purpose, a steering wheel position is corrected to a steering angle of 0° when driving straight ahead, when the driver is not holding the steering wheel in their hands. DE 10 2014 204 461 A1 discloses a method for improving the straight-ahead stability of a vehicle. Yaw rate, lateral acceleration, and a steering wheel angle are preferably used to identify the straight-ahead stability of the vehicle. US Pat. No. 7,725,227 B2 discloses a method for compensating for a steering influence in a vehicle steering system.

[0004] The invention is based on the object of compensating for drift phenomena such as crosswinds in order to maintain a straight vehicle movement.

[0005] The above-mentioned object is achieved by a steer-by-wire system having the features of claim 1, by a steer-by-wire system having the features of claim 8 and by a control unit program product of a steer-by-wire system having the features of claim 17. Advantageous further developments emerge from the subclaims.

[0006] These and other advantages and features will become clearer from the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The subject matter regarded as the invention is particularly disclosed and separately claimed in the claims at the end of the specification. The foregoing and other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a plan view of a vehicle crossing a roadway; Fig. 2 is a system diagram of a steer-by-wire system; Fig. 3 shows a handwheel with an angular position; Fig. 4 is a control method for a steer-by-wire system; Fig. 5A is a drift compensation method with a learning activation section; Fig. 5B is a learning activation method of a drift compensation method; Fig. 6 is a drift compensation method of a steer-by-wire system; and Fig. Figure 7 is a series of diagrams illustrating a drift-compensated steer-by-wire system. DETAILED DESCRIPTION

[0008] Steer-by-wire systems can completely or partially interrupt mechanical connections between a vehicle's steering axle and an operator interface. For example, a handwheel position or orientation sensor can detect the movement of a handwheel and transmit control signals to a roadwheel actuator for movement in the desired direction. The roadwheel actuator can be mounted on a pinion and connected to a rack to adjust the position of the roadwheel. A handwheel actuator can provide feedback to the handwheel operator, providing realistic position or torque feedback.

[0009] Crosswinds, varying tire pressures, road embankments, and many other driving phenomena can cause unnatural adjustments of the handwheel position while driving. For example, a strong and consistent crosswind can cause a vehicle traveling on a straight roadway to veer off the road. Of course, the operator can adjust the handwheel position to counteract the crosswind and maintain a straight heading. The operator may hold the handwheel in an offset position, which may feel unnatural. The control device(s) connected to the handwheel actuator and the roadwheel actuator can be configured to adjust the torques felt by the operator and maintain the vehicle in a straight heading to compensate for the crosswind forces.

[0010] Changes to the roadwheel actuator to maintain a straight course can undesirably maintain torque on the handwheel. The torque can be configured to provide the operator with an indication of crosswind while the handwheel is in a centered orientation. Therefore, the torque can be removed under these conditions to improve the operator experience. In fact, the handwheel can be in a centered position with no torque while the roadwheel is oriented to compensate for the crosswind.

[0011] Now with reference to the figures in which the invention is described with reference to specific embodiments without limiting it, Fig. 1 depicts a roadway 100. A vehicle 102 traverses the roadway. The vehicle includes road wheels 104 associated with a front axle 106 and road wheels 108 associated with a rear axle 110. The vehicle 102 has a substantially straight direction of movement 112 from a yaw axis 115. The yaw axis 115 is a vertical axis corresponding to a relative left-right movement (as depicted) of the front of the vehicle 102 with respect to the rear of the vehicle 102. That is, the yaw position about the yaw axis 115 describes the rotational movement from this perspective. Due to crosswind 118 or other phenomena, the vehicle 102 has a shifted trajectory 114 with an offset angle 116 relative to the substantially straight direction of movement 112 about the yaw axis 115. Sensors may be attached to the vehicle 102 to monitor the position, speed, or acceleration of the yaw axis 115.For example, accelerometers can be used to measure a yaw rate of movement around the yaw axis 115 or a rate of change of yaw position as yaw rate. Similarly, other vehicle signals such as lateral velocity and acceleration, vehicle speed, wheel speeds, etc., can also be obtained.

[0012] Fig. 2 shows a vehicle 102 with a steer-by-wire system 119 that includes a handwheel system 120 and a roadwheel system 140. The handwheel system 120 includes a handwheel 122, a handwheel shaft 124, and a housing or instrument panel 126 that may include a handwheel actuator 130 connected to the handwheel shaft 124 via a handwheel coupling 128. The handwheel actuator 130 may be any type of actuator, including an electric machine or other power generator. The handwheel actuator 130, in conjunction with the handwheel coupling 128, may also include a worm gear or other mechanical device for transmitting torque to the handwheel shaft 124. Therefore, the handwheel actuator 130 may be actuated by the handwheel controller 132 to transmit the appropriate torque to the handwheel 122. The handwheel controller 132 may include a processor 138 and memory for performing methods described and not described herein.

[0013] A control unit may contain any combination of processors, field-programmable gate arrays (FPGAs), or application-specific integrated circuits (ASICs). The control unit may contain volatile and non-volatile memory operable to store machine instructions from the processors and other processing mechanisms, as needed, for receiving, calculating, and controlling devices. Machine instructions may be stored in any language or representation, including but not limited to machine code, assembly instructions, C, C++, C#, PASCAL, COBAL, PYTHON, JAVA, and RUBY. It should be noted that any type of wired or wireless configuration for any of the communications is understood by the control unit. Wireless protocols such as ZIGBEE, WI-FI, BLUETOOTH, or other implementations may be used.Communication can occur via any known or unknown protocol or medium.

[0014] The handwheel controller 132 may communicate with a roadwheel controller 144 via a Controller Area Network (CAN) 134 or other communication medium or protocol. It should be appreciated that any number of controllers may perform some or all of the methods or systems described herein. That is, only one controller or any number of controllers may actuate the handwheel actuator 130 and the roadwheel actuator 142 to compensate for crosswinds. The roadwheel controller 144 is connected to a roadwheel actuator 142. The roadwheel actuator 142 may be an electric machine, a hydraulic system, or any other type of drive device. The roadwheel actuator 142 may include a rack and pinion system configured to align the roadwheels 104.

[0015] With reference to Fig. 3, the handwheel 122 is illustrated. The handwheel 122 has a handwheel orientation 166 about a handwheel axis 168. The handwheel orientation 166 may be defined relative to a predetermined handwheel zero value 164. For example, the predetermined handwheel zero value 164 corresponds to a vertical position of the handwheel 122. That is, the handwheel zero value 164 may correspond to a twelve o'clock position of the handwheel 122. The handwheel orientation 166 may be defined by an angular position 160 of the handwheel 122 with a handwheel orientation offset angle value 162.

[0016] With reference to Fig. 4 shows a control method 200 for a steer-by-wire system 119. The control method may be implemented on one of the controllers 132, 144 or on both controllers 132, 144, or certain functions may be implemented on one or both controllers 132, 144. The control method 200 includes, in block 202, a handwheel position sensor input from the handwheel 122. Block 204 receives the handwheel position sensor input from block 202 and outputs the torque at the handwheel 122 via the handwheel actuator 130. The angular position 160 of the handwheel 122 generates a position command in block 206.

[0017] The position command may include position, velocity, and acceleration when providing a command to the input of the road wheel position controller in block 212. The position control block may use closed-loop control techniques such as PID to generate a torque command for operating actuator 214. Drift compensation may be implemented after the position command is sent in block 206 by the drift compensation algorithm in block 208 and the summing block 210, so that the road wheel position is adjusted to compensate for the drift. The road wheel controller 144 controls the road wheel actuator 142 in block 214. In block 216, the road wheel actuator controls the lateral movement of the vehicle through the movement of the road wheel 104. In block 218, the rack force observer provides a torque or force indication from the rack of an expected reaction torque to the handwheel 122 for the operator.

[0018] The handwheel controller 132 may receive the torque indication in block 218 and generate a reference torque for the handwheel 122 in block 222. The rack force observer torque is adjusted by the drift compensation algorithm in block 208 and in summation block 220 to remove the feedback forces or torques associated with the drift. The handwheel controller 132 actuates the handwheel actuator 130 in block 224 to provide a response torque at the handwheel 122 so that the operator is unaware that the vehicle 102 includes a steer-by-wire system 119 and is similar to an electric power steering system. The drift compensation 208 receives an estimated rack force 414 and a handwheel angle 308, as shown in Fig. 6 shown.

[0019] With reference to Fig. 5A, Fig. 5B and Fig. 6, a learn activation control method 300 and a drift compensation method 208 are shown. The learn activation control method 300 includes inputs from a yaw rate sensor 302 and a handwheel orientation sensor 308. However, it should be appreciated that equivalent signals may be used. For example, instead of the yaw rate signal, the lateral acceleration signal or other signals, or even a combination of such signals, indicative of vehicle motion may be used. Similarly, an alternative to the handwheel orientation sensor, such as a motor angle sensor for the handwheel actuator motor, may be used to obtain the handwheel orientation after appropriate gear ratio conversion. It should be appreciated that any technology that provides the required information may be used. For example, piezoresistive or piezoelectric sensors may be used.An absolute yaw rate 306 or other similar signal including lateral acceleration and an absolute handwheel orientation 312 are inputs to the learning activation method 300. Additionally, a non-absolute handwheel angle 308 and a rack torque 414 are provided to the drift compensation method 208. Thus, the drift compensation method 208 compensates for the handwheel angle torque 422 and the rack torque 424.

[0020] Absolute values ​​of these inputs are captured in blocks 304 and 310, respectively, resulting in an absolute yaw rate 306 and an absolute handwheel orientation 312, respectively. To activate the remaining portions of the drift compensation method, the absolute yaw rate 306 and the absolute handwheel orientation 312 are compared to a predetermined handwheel orientation threshold 314 and a predetermined yaw rate threshold 320. If both the absolute yaw rate 306 and the absolute handwheel orientation 312 are less than the respective thresholds, a timer 324 may be activated. If the output of 324, elapsed time, is greater than or equal to the elapsed time threshold 326, then the control method 208 is activated. The respective thresholds may be defined based on the impact values ​​associated with the respective indications.That is, the learning activation method ensures that the control method 208 is activated only during the straight or pseudo-straight pass and not when the operator performs a turn / change of direction. The thresholds can be customized and vary depending on the vehicle and location. Thresholds can be learned and based on statistical methods.

[0021] Fig. 6 includes and illustrates a control method 208 for correcting drift in a steer-by-wire system 119. The input of the handwheel orientation sensor 308 is received by the method 208. It should be noted that the handwheel orientation 166 may be a flag connected to an analog or digital input of the controller. In block 404, an absolute value of the input of the handwheel orientation sensor 308 is captured. A predetermined deadband threshold 406 is compared to the absolute value to ensure that the drift is large enough to justify the control method 208. If the learn enable input 332 determined by the learn enable method 300 is true and the absolute value of the handwheel orientation sensor 308 is greater than the predetermined deadband threshold 406, the conditional block 412 receives the authorization operation to counteract the drift in the conditional block 416.Similarly, the cutoff frequency of the low-pass filter can be a function of the vehicle speed.

[0022] Therefore, outputs 422, 424 are generated that actuate the road wheel actuator 142 to move the road wheels 104 to counteract the crosswind 118. That is, the control method 208 operates the road wheel controller 144 such that the position command 212 to the road wheel actuator 142 angles / turns the road wheels 104 to counteract the crosswind 118 depending on the angular position 160, which corresponds to the handwheel orientation offset angle value 162. Over time, the difference between the handwheel orientation offset angle value 162 (equal to the required correction by the driver) and the predetermined handwheel zero value 164 will decrease as the road wheels 104 are angled / turned to counteract the crosswind 118 by an amount or portion thereof equal to the handwheel orientation offset angle value 162.That is, the value 162 of the handwheel orientation offset angle is equal to the required adjustment in the orientation of the road wheels 104. An adjustment by the road wheel actuator 142 corresponding to the value 162 of the handwheel orientation offset angle is required to counteract at least some of the drift caused by the crosswind 118. The compensation outputs 422, 424 update current values ​​via the merge blocks 418, 428. A rate limit 420 can be implemented to limit the rate of change for each of the compensation outputs 422, 424. Each of the outputs 422, 424 can have appropriate limits to improve the operator experience and reduce sudden changes. The rate limit block 420 limits the first derivative of the signal passing through it. The output will not change faster than the specified limit.The upper and lower limits can also be a function of the vehicle speed. In this case, the speed limit block 420 applies the speed limit separately to the outputs of 418 and 428. Alternatively or additionally, a low-pass filter block can be used.

[0023] In the latch block 426, the values ​​of the previous cycle are held in the unit delay blocks 430, 432 if the input of AND gate 410 is false. Therefore, the control method 208 is not executed, and the previous values ​​(without drift compensation) are used.

[0024] With reference to Fig.7, system performance graphs 500 are shown. In graph 501, a curve 502 shows the handwheel orientation offset angle value 162 when the vehicle 102 is subjected to a crosswind 118 or other drifting phenomena without the disclosed control method. In graph 503, a curve 504 represents the handwheel torque caused by the torque control block 224 when the vehicle 102 is subjected to a crosswind 118 or other drifting phenomena without the disclosed control method.

[0025] In graph 505, curve 502 is compared to curve 506 with the control method 208 implemented as described, showing that the handwheel orientation offset angle value 162 reaches a predetermined deadband threshold 406 over time according to the control method 208.

[0026] In graph 507, curve 504 is compared to curve 508 with the control method 208 implemented as described, showing that the handwheel torque from the handwheel torque control block 224 decreases to or approaches zero over time according to the control method 208 as the feedback torque from the rack observer 218 is compensated by the drift compensation algorithm 208.

[0027] Although the invention has been described in detail in connection with only a limited number of embodiments, it is readily understood that the invention is not limited to the disclosed embodiments. Rather, the invention may be modified to include any number of variations, changes, substitutions, or equivalent arrangements not previously described, but which are within the spirit and scope of the invention. Furthermore, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be considered limited by the foregoing description.

Claims

[1] Steer-by-wire system (119), the system (119) comprising: a controller (144) operable in response to a handwheel orientation (166) defined by an angular position (160) of a handwheel (122) having a handwheel orientation offset value (162) corresponding to a substantially straight desired direction of movement (112) with respect to a predetermined handwheel zero value (164), and at least one yaw rate (306) associated with a rate of change of a yaw position about a yaw axis (115) that is less than a predetermined yaw rate threshold value (320) or a lateral acceleration that is less than a predetermined lateral acceleration threshold value, to actuate a roadwheel actuator (142) for aligning roadwheels (104) such that a position command (212) to the roadwheel actuator (142) based on the handwheel orientation (166) corresponds to the handwheel orientation offset value (162) in the opposite direction,to reduce a difference between the handwheel orientation offset value (162) and the predetermined handwheel zero value (164) when the road wheels (104) are angled / turned. [2] The steer-by-wire system (119) of claim 1, wherein the controller (144) is operable to actuate the road wheel actuator (142) to reduce the difference until the predetermined handwheel zero value (164) corresponds to the substantially straight desired direction of travel (112). [3] Steer-by-wire system (119) according to claim 1, wherein the substantially currently desired direction of movement (112) is defined by a predetermined deadband threshold value (406). [4] The steer-by-wire system (119) of claim 1, wherein the controller (144) is further operable to receive the handwheel orientation (166) and the yaw rate (306). [5] The steer-by-wire system (119) of claim 1, wherein the controller (144) is further operable to receive instructions to actuate the road wheel actuator (142) based on the handwheel orientation offset value (162) and the yaw rate (306) to reduce the difference. [6] The steer-by-wire system (119) of claim 1, wherein the road wheel actuator (142) is a power steering electric motor configured to actuate a pinion gear connected to a rack. [7] The steer-by-wire system (119) of claim 1, wherein the road wheel actuator (142) is actuated in response to the handwheel orientation offset value (162) being less than a predetermined handwheel orientation threshold value (314). [8] Steer-by-wire system (119), the system (119) comprising: a handwheel actuator (130); and a controller (132) operable to actuate the handwheel actuator (130) when a handwheel orientation (166) defined by an angular position (160) of a handwheel (122) has a handwheel orientation offset value (162) corresponding to a substantially straight desired direction of movement (112) with respect to a predetermined handwheel zero value (164), and at least one of a yaw rate (306) associated with a rate of change of yaw position about a yaw axis (115) is less than a predetermined yaw rate threshold (320) or a lateral acceleration is less than a predetermined lateral acceleration threshold, such that a torque command to the handwheel actuator (130) based on a rack force observer has a magnitude in an opposite direction to reduce a difference between a handwheel torque and a steady-state drag torque. [9] The steer-by-wire system (119) of claim 8, wherein the predetermined handwheel zero value (164) is less than a predetermined handwheel orientation threshold value (314). [10] The steer-by-wire system (119) of claim 9, wherein the handwheel torque is derived from actuation of the roadwheel actuator (142) based on the handwheel orientation offset value (162) at the handwheel orientation (166) and the predetermined handwheel zero value (164). [11] Steer-by-wire system (119) according to claim 9, wherein the handwheel torque is equal to the steady-state resistance torque when the predetermined handwheel zero value (164) corresponds to the substantially straight desired direction of movement (112). [12] Steer-by-wire system (119) according to claim 11, wherein the substantially currently desired direction of movement (112) is defined by a predetermined deadband threshold value (406). [13] The steer-by-wire system (119) of claim 9, wherein the controller (132) is further operable to receive the handwheel orientation (166) and the yaw rate (306). [14] The steer-by-wire system (119) of claim 9, wherein the controller (132) is further operable to receive instructions to actuate the handwheel actuator (130) based on the handwheel orientation offset value (162) and the yaw rate (306) to reduce the difference. [15] The steer-by-wire system (119) of claim 9, wherein the handwheel actuator (130) is a handwheel electric motor configured to apply the handwheel torque to the handwheel (122). [16] The steer-by-wire system (119) of claim 9, wherein the predetermined handwheel orientation threshold (314) is based on a vehicle speed. [17] Control unit program product of a steer-by-wire system (119), the control unit program product comprising: a storage medium readable by a control unit (132) with program instructions executed thereon and executable by a control unit (132) in order to receive a handwheel orientation (166) defined by an angular position (160) of a handwheel (122) having a handwheel orientation offset value (162) corresponding to a substantially straight desired direction of movement (112) with respect to a predetermined handwheel zero value (164) that is less than a predetermined handwheel orientation threshold value (314), receive at least one yaw rate (306) associated with a rate of change of a yaw position about a yaw axis (115) that is less than a predetermined yaw rate threshold (320); or to receive a lateral acceleration that is less than a predetermined lateral acceleration threshold; and actuate a handwheel actuator (130) such that a torque command to the handwheel actuator (130) based on a rack force observer has a magnitude corresponding to the handwheel orientation offset value (162) in the opposite direction to reduce a difference between a handwheel torque and a steady-state drag torque. [18] The controller program product of claim 17, further comprising actuating a road wheel actuator (142) such that a position command (212) to the road wheel actuator (142) based on the handwheel orientation (166) has the magnitude corresponding to the handwheel orientation offset value (162) in the opposite direction to reduce the difference between the handwheel orientation offset value (162) and the predetermined handwheel zero value (164). [19] The controller program product of claim 18, wherein the road wheel actuator (142) is actuated to reduce the difference until the predetermined handwheel zero value (164) corresponds to the substantially straight desired direction of movement (112). [20] Control device program product according to claim 19, wherein the substantially currently desired direction of movement (112) is defined by a predetermined deadband threshold value (406).

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