Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention:
[0001] The present invention relates to a steering wheel actuator for a Steer-By-Wire (SbW) system of a vehicle and method thereof.

Background of the invention:
[0002] In a conventional Electric Power Steering (EPS) system, a driver input is detected, and the EPS system assists the driver by providing a portion of torque as assist torque. The road forces are transmitted via an intermediate shaft to the driver and act as a closed loop path to the driver. There exists fail safe even in case of complete failure of servo drive because of mechanical backup. In a steer-by-wire (SbW) system, the road forces are simulated via Force Feedback Unit (FFU) as a steer feel torque to the driver. When the FFU loses both the controllers, passive steer feel is required for the controllability of vehicle. Both the controllers corresponds to two independent controller namely a primary controller and secondary controller within a control device for the steering wheel actuator to have higher ASIL rating. If the driver intention via steering angle/torque signal cannot be measured, then the lateral control of the vehicle is not possible.

[0003] Controllability of the vehicle by the driver is of paramount importance during any driving maneuver. In SbW system, redundancy in terms of dual controllers/channels is available in both steering wheel actuator (SWA) and steering rack actuator (SRA) subsystems. In driver steer mode (driver is responsible for the control of the vehicle), steering wheel angle sensor (SAS) output from SWA is one of the main inputs to SRA that determines the front wheel angle of the vehicle through the rack actuation. In SWA, the FFU simulates the active feedback torque based on inputs like rack force, vehicle speed etc. In dual controller failure (FFU failure) and to provide a passive steer feel, a controllable passive steer feel torque is currently achieved by short circuiting the motor phases by triggering the MOSFETs in the control device of the steering wheel actuator. A continuous active power supply is required to do this trigger and provide passive steer feel when driver applies steering wheel motion. In active steering operation (esp. in driver steer mode), for the ECU processing and sensor functioning and to make rack position request to SRA and during passive mode change, continuous power supply is vital in the conventional design.

[0004] Thus in the conventional SWA, the motor provides the feedback torque if power supply is available. In case of power supply OFF, the mechanical frictional element is required to avoid free rotation. The motor is used for providing both feedback and angle adjustment. A moderate power consumption with current rating in the range of 25A - 50A. The current design/system is having homogeneous redundancy. Both the primary and secondary actuator and the control logic remains identical. So, if there is a systematic failure or if there is a common cause failure, then this can affect both primary and secondary channels and this can lead to the availability issues or failure of the SWA.

[0005] According to a prior art CN107458456, a steering-by-wire system based on hydraulic inerter is disclosed. The invention provides a steering-by-wire system based on a hydraulic inerter. The steering-by-wire system comprises a steering wheel, an upper steering column, a gear rack transmission mechanism, the hydraulic inerter, an aligning motor, a front axle, a steering motor, an ECU, an angle sensor and the like. Magnetorheological fluid is integrated to the hydraulic inerter, the viscosity of the magnetorheological fluid is changed by changing the magnetic induction intensity of the periphery of the hydraulic inerter, and accordingly, the purpose of adjusting the damping force of the hydraulic inerter is achieved. The road feel of steering inertia of the steering wheel is simulated through the dynamic inertial effect of the hydraulic inerter, and the steering assistance and feedback force are optimally designed through the adjustable damp characteristic of the magnetorheological fluid in the hydraulic inerter. Compared with traditional steering-by-wire devices, through the steering-by-wire system, the road simulation function of steering wheel is achieved better, and the control stability and driving safety of a vehicle are improved.

Brief description of the accompanying drawings:
[0006] An embodiment of the disclosure is described with reference to the following accompanying drawings,
[0007] Fig. 1 illustrates a block diagram of a steering wheel actuator for a steer-by-wire (SbW) system of a vehicle, according to an embodiment of the present invention, and
[0008] Fig. 2 illustrates a method for operating the steering wheel actuator of the Steer-By-Wire (SbW) system of the vehicle, according to the present invention.

Detailed description of the embodiments:
[0009] Fig. 1 illustrates a block diagram of a steering wheel actuator for a steer-by-wire (SbW) system of a vehicle, according to an embodiment of the present invention. A vehicle 102 is shown with Steer-by-Wire (SbW) system 100 comprising a steering wheel actuator 110 and a steering rack actuator 120. The steering wheel actuator 110 is mechanically coupled with a steering wheel 104 and electronically connected to a steering rack actuator 120. The steering wheel actuator 110 powered by a vehicle battery 124. The steering wheel actuator 110 comprises a rotatable electric machine 114, a Magneto-Rheological (MR) damper 116 (also known as active MR damper), and a control device 122 connected to the rotatable electric machine 114 and the MR damper 116. The control device 122 configured to operatively control the rotatable electric machine 114 and the MR damper 116 to provide active feedback to a driver and to provide steering assistance, characterized in that, the steering wheel actuator 110 is powered and operable even under unavailability of power supply from the vehicle battery 124. The operatively controlling of the rotatable electric machine 114 and the MR damper 116 corresponds to controlling each as per the requirement, i.e. for assistance, or for dampening and either completely or partially, etc, which is predetermined as per the requirement.

[0010] The steering wheel actuator 110 also comprises an adjustable steering column adjustment 106. The gear mechanism (or mechanical gear unit) 112 reduces speed and increase the torque at driver side. The control device 122 calculates the needed feedback based on the vehicle driving scenario like vehicle speed and the road feedback from steering rack actuator 120. The needed steering feedback is provided by either giving a counter torque or by actively damping the movement of the steering wheel 104. The steering wheel actuator 110 comprises the rotatable electric machine 114 and the Magneto Rheological fluid based active damper 116. The vehicle battery 124 or power supply is used to power both steering wheel actuator 110 and the steering rack actuator 120. A steering angle sensor (SAS) is used to determine the steering wheel angle information. The present invention focuses on a heterogeneous redundancy in steering wheel actuator (SWA) 110 for providing steering road feedback to the driver by using the MR damper 116 to provide the necessary feedback torque. The rotatable electric machine 114 fulfills the steering position request-based actuation and/or provide feedback torque to the driver and/or generate voltage/current while operating in a generotoric mode.

[0011] According to an embodiment of the present invention, the steering wheel actuator 110 is powered by at least one of the rotatable electric machine 114 and a power storage unit 118. According to an embodiment, the power storage unit 118 is provided as an additional component for the steering wheel actuator 110 which is either internal to a housing of the steering wheel actuator 110 or is externally connected. The rotatable electric machine 114 is operable as generator on rotation of the steering wheel 104.

[0012] According to an embodiment of the present invention, the power storage unit 118 is selected from a group comprising an auxiliary battery and a capacitor bank. The power is supplied to a load which is at least one selected from a group comprising the MR damper 116, the at least one sensor 108, and the control device 122. The power/energy generated is either directly provided by the rotatable electric machine 114 or through the power storage unit 118. The at least one sensor 108 is selected from a group comprising a steering angle sensor and torque sensor but not limited to the same.

[0013] According to an embodiment of the present invention, the signal detected by the at least one sensor 108 is transmitted to the Steering Rack Actuator (SRA) 120 of the SbW system 100. Thus, in the event of loss of power supply to the steering wheel actuator 110, the control device 122 is still able to provide signals to the steering rack actuator 120 and control the steerability of the vehicle 102.

[0014] According to the present invention, the control device 122 is provided with a controller with necessary signal detection, acquisition, and processing circuits. The controller is a control unit which comprises memory element such as Random Access Memory (RAM) and/or Read Only Memory (ROM), Analog-to-Digital Converter (ADC) and a Digital-to-Analog Convertor (DAC), clocks, timers, counters and at least one processor (capable of implementing machine learning) connected with each other and to other components through communication bus channels. The memory element is pre-stored with logics or instructions or programs or applications or modules/models and/or threshold values, which is/are accessed by the at least one processor as per the defined routines. The internal components of the controller are not explained for being state of the art, and the same must not be understood in a limiting manner. The controller may also comprise communication units to communicate with an external computing device such as the cloud, a remote server, etc., through wireless or wired means such as Global System for Mobile Communications (GSM), 3G, 4G, 5G, Wi-Fi, Bluetooth, Ethernet, serial networks, and the like. The controller is implementable in the form of System-in-Package (SiP) or System-on-Chip (SOC) or any other known types.

[0015] According to the present invention, a working example of the steering wheel actuator 110 is provided. Consider the vehicle 102 with SbW system 100. The steering wheel actuator 110 and steering rack actuator 120 are electronically connected. Assume there is a cut in the connection between the vehicle battery 124 to the steering wheel actuator 110, or there is some fault because of which the power to the steering wheel actuator 110 is unavailable. In this scenario, the availability of the SbW system 100 should be ensured. When the driver rotates the steering wheel 104, the rotatable electric machine 114 is also rotates. Since the rotatable electric machine 114 is coupled through a gear mechanism 112, a minor or slight rotational movement of the steering wheel 104 leads to higher rotation of the rotatable electric machine 114 due to the same gear mechanism 112. The rotation of the rotatable electric machine 114 generates electrical energy as it is rotated in generator mode and the generated power is supplied to the load selected from a group comprising the MR damper 116, the control device 122, the at least on sensor 108 and the power storage unit 118. The generated electrical energy is either directly supplied to the loads or through the power storage unit 118 once it is charged. The vehicle 102 can then be operated in limp-home mode or to nearest service station for repair before causing any accidents.

[0016] According to an embodiment of the present invention, the operation of the rotatable electric machine 114 in generator mode is automatically activated by the control device 122. The control device 122 detects the unavailability of the power supply through known means or is indicated by vehicle control unit of the vehicle 102. The same is indicated to the driver and the rotatable electric machine 114 is enabled to be operated in generator mode.

[0017] According to an embodiment of the present invention, a Steer-By-Wire (SbW) system 100 of the vehicle 102 is provided. The SbW system 100 comprises the steering wheel actuator 110 and the steering rack actuator 120. The steering wheel actuator 110 mechanically coupled with the steering wheel 104 and electronically connected to the steering rack actuator 120. The steering wheel actuator 110 comprises the rotatable electric machine 114, the Magneto-Rheological (MR) damper 116, and the control device 122 connected to the rotatable electric machine 114 and the MR damper 116. The control device 122 configured to operatively control the rotatable electric machine 114 and the MR damper 116 to provide active feedback to the driver and to provide steering assistance, characterized in that, the steering wheel actuator 110 is powered by and operable even under unavailability of power supply from the vehicle battery 124.

[0018] According to an embodiment of the present invention, the steering wheel actuator 110 is powered by at least one of the rotatable electric machine 114 and the power storage unit 118. The rotatable electric machine 114 is operable as generator on rotation of the steering wheel 104 and supply power to the load which is at least one selected from a group comprising the MR damper 116, at least one sensor 108, the control device 122 and the power storage unit 118 (for charging).

[0019] According to an embodiment of the present invention, the power storage unit 118 is selected from the group comprising the auxiliary battery and the capacitor bank. The power supply to the at least one of the MR damper 116, the at least one sensor 108, and the control device 122 is provided by at least one of the rotatable electric machine 114, the auxiliary battery and the capacitor bank.

[0020] According to an embodiment of the present invention, the signal detected by the at least one sensor 108 is transmitted to the Steering Rack Actuator (SRA) 120 of the SbW system 100. Thus, in the event of loss of power supply to the steering wheel actuator 110, the control device 122 is still able to provide signals to the steering rack actuator 120 and control the steerability of the vehicle 102.

[0021] According to the present invention, the steering wheel actuator 110 is provided for full steer-by-wire systems 100, where no mechanical connection exists between the steering wheel actuator 110 and the steering rack actuator 120, as well as for partial steer-by-wire system 100 where a mechanical coupling can be engaged in case of fail-safe operations. The heterogeneous redundant SbW system 100 is used to provide the needed steering feedback by utilizing the rotating electric machine 114 and the active MR damper 116. Thus, enabling more availability of the SbW system 100 from common cause failures to steering wheel actuator 110. The active MR damper 116 contributes the major part of steering feedback by selective damping based on controlling the current, the electric machine 114 uses the fail operational scenarios and the steering wheel positioning applications. This enables the reduction in sizing and packaging of the rotating electric machine 114 and thus the flexibility of steering wheel actuator 110. In a full steer-by wire system 100, since there is no mechanical coupling with the rack, the steering wheel 104 is freely movable when the steering wheel actuator 110 is not activated. To support the driver to get in and get out of the vehicle 102, the steering wheel actuator 110 need to prevent the movement of the steering wheel 104. With an active MR damper 116, this is achieved with a low form factor compared to that with the rotating electric machine 114.

[0022] In the event of power loss to the steering wheel actuator 110, by using the rotating electric machine 114 in generatoric mode by default and the current generated by the steering wheel rotation is fed to the active MR damper 116 in a controlled way, the steering wheel actuator 110 provides the sufficient feedback. This eliminates the need of a mechanical frictional element and this improves the efficiency of the SbW system 100. For protecting the driver airbag wiring harness, the rotation of steering wheel 104 needs to be limited. With an active MR damper 116, within a small form factor of steering wheel actuator 110, the non-over steerable steering wheel limitation can achieve. With the steering wheel actuator 110 rotated in generatoric mode, the power generated in terms of current and voltage is sufficient to run both the MR damper 116 as well as the control device 122, and this can provide an end stop torque to limit the angular rotation of the steering wheel, thus protecting the wiring harness provided to the Airbag in the steering wheel 104.

[0023] As compared to rotating electric machine 114 providing the steering feedback by the counter torque, the MR damper 116 is only absorbing the driver force and providing the needed steering feedback. The rotating electric machine 114 can cause a sudden unwanted lateral movement of the vehicle 102 if the driver suddenly takes his hand from steering wheel 104. The MR damper 116 does not lead to the stability of the vehicle 102 since there is no counter torque provided. The noise in the SbW system 100 can effectively attenuate with the active MR dampers 116. Since there are no steering wheel position changes due to noise in the feedback from steering rack actuator 120, the noise does not propagate back to steering rack actuator 120 again. But the necessary high frequency feedback can be felt with the help of the rotating electric machine 114. The driver intended torque can be estimated as a function of rate of change of damping torque provided by the active MR damper 116 and the rate of change in steering wheel angle from steering angle sensor. This helps to detect the Hands ON or Hands OFF scenario without the use of a dedicated torque sensor. With less power or even without an external power, the system 100 is able to provide the feedback, so the steering wheel actuator 110 is usable for gaming support in futuristic vehicle 102.

[0024] Fig. 2 illustrates a method for operating the steering wheel actuator of the Steer-By-Wire (SbW) system of the vehicle, according to the present invention. The steering wheel actuator 110 mechanically coupled with the steering wheel 104 and electronically connected to the steering rack actuator 120. The steering wheel actuator 110 powered by the vehicle battery 124. The steering wheel actuator 110 comprises the rotatable electric machine 114 and the Magneto-Rheological (MR) damper 116, characterized by, while power supply is unavailable from the vehicle battery 124, the method comprises plurality of steps of which a step 202 comprises generating electric energy upon manual rotation of the rotatable electric machine 114 as generator through the steering wheel 104. A step 204 comprises supplying energy to the load through the generated electric energy.

[0025] According to the method of the present invention, the load is at least one selected from a group comprising the MR damper 116, at least one sensor 108, the control device 122 and the power storage unit 118 (for charging). The power storage unit 118 is selected from the group comprising the battery and capacitor bank. The power supply to the load is provided by at least one of the rotatable electric machine 114, the battery and the capacitor bank. The rotatable electric machine 114 either supplies the energy/power to the load directly or through the battery or the capacitor bank.

[0026] According to the method of the present invention, the signal detected by the at least one sensor 108 is transmitted to the Steering Rack Actuator (SRA) 120 of the SbW system 100. Thus in the absence of power supply to the steering wheel actuator 110, the information from the at least one sensor 108 is provided to the SRA 120 to maintain the drivability/steerability of the vehicle 102.

[0027] According to the present invention, the steering wheel actuator 110 for providing road feedback to the driver in full is provided. Alternatively, the Steer-by-Wire (SbW) system 100 with heterogeneous redundancy and it’s availability is provided. Since the damping torque is mainly contributed by MR damper 116, this enables less power consumption (for example only ~2 A for 20 Nm Torque) compared to a Force Feedback type steering wheel actuator 110 that relies mainly on the rotating electric machine 114. Since the torque requirement of the rotating electric machine 114 is reduced the overall size of the steering wheel actuator 110 is reduced and this helps in packaging flexibility. One of the main challenges of Steer-by-Wire (SbW) system 100 is its availability. Since there is no mechanical connection between the steering wheel actuator 110 and the steering rack actuator 120, in case of non-availability of SbW system 100, the driver cannot steer the vehicle 102 to the desired trajectory. For that redundant channels and multiple power sources are mostly used. However, in the present invention, the use of heterogeneous redundant channel increases the availability of the SbW system 100 from common cause failures. Another focus is on power supply failure scenario, by operating the rotating electric machine 114 in generatoric mode, the rotating electric machine 114 produces electric current based on movement of the steering wheel 104, and this current is provided to the MR damper 116 circuit to provide active feedback and to the steering wheel angle sensor as one of the at least one sensor 108 to its operation and other loads. So, even with power supply failure, the steering wheel actuator 110 provides the needed feedback to the driver in a controlled manner as like in power supply ON.

[0028] According to the present invention, the rotating electrical machine 114 is operated in generatoric mode which provides needed active torque even in power OFF conditions. There is no need for mechanical friction since system 100 is able to provide active feedback in power supply lost scenarios as well, leading to higher efficiency. The rotating electric machine 114 is mainly used for steering angle adjustments, leading to less sizing. In addition, due to low size and specific use case, the rotatable electric machine 114 consumes less power (~2 A for 20 Nm feedback). The present invention is more resistant to common cause failure, with fast response time, no stick slip effect and no electric motor cogging effect. Since less power or no power required, the steering wheel actuator 110 is usable for gaming support in futuristic vehicle 102.

[0029] It should be understood that the embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.
, Claims:1. A steering wheel actuator (110) of a Steer-By-Wire (SbW) system (100) of a vehicle (102), said steering wheel actuator (110) mechanically coupled with a steering wheel (104) and electronically connected to a steering rack actuator (120), said steering wheel actuator (110) powered by a vehicle battery (124), said steering wheel actuator (110) comprises:
a rotatable electric machine (114),
a Magneto-Rheological (MR) damper (116), and
a control device (122) connected to said rotatable electric machine (114) and said MR damper (116), said control device (122) configured to operatively control said rotatable electric machine (114) and said MR damper (116) to provide active feedback to a driver and to provide steering assistance, characterized in that, said steering wheel actuator (110) is powered by and operable even under unavailability of power supply.

2. The steering wheel actuator (110) as claimed in claim 1, wherein said steering wheel actuator (110) is powered by at least one of said rotatable electric machine (114) and a power storage unit (118), wherein said rotatable electric machine (114) is operable as generator on rotation of said steering wheel (104).

3. The steering wheel actuator (110) as claimed in claim 2, wherein said power storage unit (118) is selected from a group comprising an auxiliary battery and capacitor bank.

4. The steering wheel actuator (110) as claimed in claim 3, wherein power is supplied to at least one load selected from a group comprising said MR damper (116), at least one sensor (108), said control device (122) and said power storage unit (118).

5. The steering wheel actuator (110) as claimed in claim 2, wherein said signal detected by said at least one sensor (108) is transmitted to a Steering Rack Actuator (SRA) (120) of said SbW system (100).

6. A Steer-By-Wire (SbW) system (100) of a vehicle (102), said SbW system (100) comprises a steering wheel actuator (110) and a steering rack actuator (120), said steering wheel actuator (110) mechanically coupled with a steering wheel (104) and electronically connected to said steering rack actuator (120), said steering wheel actuator (110) comprises:
a rotatable electric machine (114),
a Magneto-Rheological (MR) damper (116), and
a control device (122) connected to said rotatable electric machine (114) and said MR damper (116), said control device (122) configured to operatively control said rotatable electric machine (114) and said MR damper (116) to provide active feedback to a driver and to provide steering assistance, characterized in that, said steering wheel actuator (110) is powered by and operable even under unavailability of power supply.

7. A method for operating a steering wheel actuator (110) of a Steer-By-Wire (SbW) system (100) of a vehicle (102), said steering wheel actuator (110) mechanically coupled with a steering wheel (104) and electronically connected to a steering rack actuator (120), said steering wheel actuator (110) comprises a rotatable electric machine (114) and a Magneto-Rheological (MR) damper (116), said steering wheel actuator (110) powered by a vehicle battery (124), characterized by, while power supply is unavailable from said vehicle battery (124), said method comprising the steps of,
generating electric energy upon manual rotation of a rotatable electric machine (114) as generator through said steering wheel (104); and
supplying energy to a load through said generated electric energy.

8. The method as claimed in claim 7, wherein said load is at least one selected from a group comprising said MR damper (116), at least one sensor (108), a control device (122) and a power storage unit (118), wherein said power storage unit (118) is selected from a group comprising a battery and capacitor bank.

9. The method as claimed in claim 8, wherein said power supply to said load is provided by at least one of said rotatable electric machine (114), said battery and said capacitor bank.

10. The method as claimed in claim 7, wherein said signal detected by said at least one sensor (108) is transmitted to said Steering Rack Actuator (SRA) (120) of said SbW system (100).