System Architecture for Functional Safety of Active Steer-by-Wire Systems

Abstract

The disclosed invention is a force feedback system for use in a steer-by-wire vehicle that provides active haptic feedback to the vehicle operator and provides safe control of the steer-by-wire vehicle. The disclosed invention is also a method for safely returning the steering control system of a steer-by-wire vehicle to a center position.

Description

[Background technology]

[0001] In prior art vehicle steering systems, the steering system includes a mechanical mechanism, such as a positive caster, that forces the steering wheel to return to a center position (zero wheel angle) after each steering input by the operator. The effect provided by such a positive caster configuration increases with vehicle speed. Thus, the positive caster mechanical mechanism improves vehicle stability and provides a good centering feel. Current steer-by-wire systems lack the steering linkage necessary to provide the active operator feedback and return-to-center functionality of prior art steering systems.

[0002] A steer-by-wire input device with active haptic feedback must provide an acceptable level of functional safety by providing accurate angular position sensing and preventing unintended movement of the steering input shaft and unintended haptic feedback.

[0003] The exemplary embodiments disclosed herein overcome the shortcomings of current steer-by-wire systems and add functional safety to the overall system. As an additional advantage, the disclosed embodiments can be integrated into current steer-by-wire systems installed on land and water vehicles. Summary of the Invention

[0004] The disclosed invention is a force feedback system. The force feedback system includes a steering shaft, a Hall sensor magnet supported on the steering shaft, an electrically controlled brake configured to engage the steering shaft, an electronically controlled motor configured to engage the steering shaft, at least one power source, a brake drive amplifier, and a motor drive amplifier. The brake drive amplifier receives power from the at least one power source, and the brake drive amplifier supplies current to the electronically controlled brake. The force feedback system further includes a motor drive amplifier, which receives power from the at least one power source, and the motor drive amplifier supplies current to the electronically controlled motor. Additionally, the force feedback system includes a first pair of angular position sensors and a steering input controller. The first pair of angular position sensors receives power from the at least one power source. A vehicle controller is in data communication with the first pair of angular position sensors and the steering input controller. The force feedback system may include a second pair of angular position sensors, a second power source, and a third power source. Additionally, the force feedback system may include a main microcontroller and a safety or backup microcontroller.

[0005] The present disclosure further provides a method for returning a steering control system of a vehicle to a center position, the method comprising: the vehicle having at least one steering wheel capable of adjusting the steering control system over a range of angular orientations that includes a center position of the steering control system; a steering control system including an electric motor and a steering input controller, the steering input controller controlling operation of the electric motor to directly or indirectly control wheel angle; a steering control system including a force feedback device in data communication with a vehicle steering controller, the force feedback device including at least one angular position sensor, an electric motor, an electrically actuated brake, and a microcontroller; The method comprises the following steps: transmitting data provided by the at least one angular position sensor to a vehicle controller; transmitting data from the wheel angle sensors and the vehicle speed sensor to a vehicle controller; a vehicle controller analyzing the received data to thereby detect a fault in any one of the at least one angular position sensor; the microcontroller initiating closed loop operation to effect a change in wheel angular orientation; the microcontroller defining a value for the target parameter using the data received by the microcontroller, where a zero value corresponds to a center position of the steering control of the vehicle; a microcontroller managing operation of the feedback device, thereby controlling operation of the electric motor to drive the target parameter to a zero value; Includes. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 illustrates an exemplary embodiment of a system architecture for improving the safe operation of a steer-by-wire system. [Figure 2] FIG. 2 is a block diagram of elements of a force feedback device (FFD) suitable for use in the exemplary embodiment of FIG. 1. [Figure 3A] FIG. 1 is a control flow diagram of operations for managing and safe operation of the electric motor components of the FFD. [Figure 3B] FIG. 1 is a control flow diagram of operations for managing and safe operation of the electric motor components of the FFD. [Figure 4A]FIG. 8 is a process flow diagram of a safety loop that provides safe operation of the electrically controlled motor shown in FIGS. 2 and 7. [Figure 4B] FIG. 8 is a process flow diagram of a safety loop that provides safe operation of the electrically controlled motor shown in FIGS. 2 and 7. [Figure 5A] FIG. 8 is a process flow diagram of a safety loop that provides safe operation of the electrically controlled brake shown in FIGS. 2 and 7. [Figure 5B] FIG. 8 is a process flow diagram of a safety loop that provides safe operation of the electrically controlled brake shown in FIGS. 2 and 7. [Figure 6] FIG. 1 illustrates another exemplary embodiment of a system architecture for improving the safe operation of a steer-by-wire system. [Figure 7] FIG. 7 is a block diagram of elements of a force feedback device (FFD) suitable for use in the exemplary embodiment of FIG. 6. [Figure 8] FIG. 1 is a control flow diagram of operations for management and safe operation of electrically actuated brake components of an FFD. DETAILED DESCRIPTION OF THE INVENTION

[0007] The drawings included in this application illustrate certain aspects of the embodiments described herein. However, the drawings should not be construed as limiting the embodiments. The disclosed subject matter is capable of considerable modification, alteration, combinations, and equivalents in form and function, as will occur to those skilled in the art having the benefit of this disclosure.

[0008] The present disclosure may be more readily understood by reference to these detailed descriptions. For brevity and clarity of description, reference numerals may be repeated among the different figures, where appropriate, to indicate corresponding or analogous elements. The following description is not intended to limit the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate the details and features of the present disclosure. Furthermore, the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless specifically indicated as such.

[0009] Throughout this disclosure, the terms "about," "approximate," and variations thereof are used to indicate that values ​​include inherent variation or error in the device, system, or measurement method employed, as would be recognized by one of ordinary skill in the art.

[0010] 1-2 and 6-7 present exemplary embodiments of an improved force feedback system. The force feedback system can be integrated into existing steer-by-wire systems installed on land and water vehicles. The force feedback system generates active feel or feedback to the vehicle operator based on the vehicle state and the integration of target parameters, which are described in detail below. Additionally, the force feedback system provides functional safety task separation between the force feedback device 20 and the vehicle's native systems.

[0011] Each embodiment includes a force feedback device 20 suitable for returning a directional control element, such as a steering wheel 16 or control wheel 16, to center using a combination of an electric motor 24 and an electric brake 22 mounted in series with a steering shaft 18 that supports the steering wheel 16. As described in more detail below, for purposes of vehicle operation, center may be defined by any number of vehicle parameters. The force feedback device (FFD) 20 measures the current position of the steering wheel 16 using one or more angular position sensor pairs 44, 46 and also reads the current state of the vehicle via a CAN bus 52. For simplicity, the remainder of this disclosure will refer to this as a CAN bus 52, although any suitable digital communication bus will suffice. A microcontroller 50 uses this information to control the electric motor 24 to apply sufficient torque to return the steering shaft 18 and steering wheel 16 to the defined center position, and / or to control the brake 22 to apply sufficient torque to provide haptic feedback to the operator. To improve safe vehicle operation, the exemplary system architecture performs three primary tasks: The three primary tasks are (i) transmitting accurate angular position and diagnostic information to the vehicle (directly or indirectly), (ii) preventing unintended motor operation, and (iii) preventing steering lock due to unintended current flow in the electric brake coils. Furthermore, the exemplary system architecture provides safety task separation between the steering input controller and the vehicle steering controller. Thus, while continuously executing a feel algorithm used to drive the target parameter to zero, the microcontroller 50 also monitors the angular position sensors 44, 46, the brake drive amplifier 38, and the motor drive amplifier 42. An example of a suitable algorithm is provided in FIGS. 4A and 4B. For the remainder of this disclosure, centering the steering shaft 18 will be referred to as returning to the target parameter. Thus, mathematically, centering the steering shaft 18 is equivalent to forcing the target parameter to zero.

[0012] Before describing the two exemplary embodiments described herein, the following definitions are helpful in understanding the terminology in the process flow diagrams of FIGS. Motor torque control logic -including various types of closed-loop feedback control methods, such as proportional control (P), proportional-integral control (PI), proportional-integral-derivative control (PID) or other similar methods suitable for closed-loop feedback control; -The output is the desired motor torque (T COMMAND , Figure 3A); Motor torque constant - the motor winding current (I) required to generate the desired motor torque COMMAND , Figure 3B) to calculate the value; -Usually provided by the motor manufacturer; Motor current control -Controls the motor winding amplifier to draw the required current (I MOTOR , Figure 3B) to the windings, also known as "motor commutation"; - For example, trapezoidal control, sine wave control and field oriented control; Motor operation -Torque due to current flowing through the motor windings (T STEER , Figure 3B); Steering angle position sensor - Angular position sensors 44, 46 are used to measure the angular position (θ STEER ) is measured; Steering system dynamics - the torque (T STEER ) movement of the steering shaft 18; The generated torque overcomes the inertia and friction of the steering shaft 18 and the wheel 16, creating a rotational movement of the steering wheel 16 attached to the steering shaft 18; Scaling and saturation - mathematical operations are performed by the microcontroller 50, 50a, 50b, which executes control logic based on information received from the vehicle steering controller 14, thereby calculating target parameters and generating the desired behavior (e.g., response time) of the steering system; Vehicle steering controller 14 In the exemplary embodiment of FIGS. 1 and 6, a road wheel angle (RWA) sensor 12 (the sensor 12 detects the road wheel angle or steering angle θ RWA The FFD 20 reads the original equipment vehicle sensors (providing

[0013] The following definitions are helpful in understanding the terminology in the process flow diagram of FIG. Brake operation -Brake coil current (I BRAKE ) flows through the brake coil, generating a brake torque (T BRAKE ) occurs; Brake feel logic -Consists of an algorithm that uses steering angle position measurements to calculate the required tactile feel (end-stop feel, steering speed proportional feel, etc.); - The output is the command brake current (I COMMAND,BRAKE ) is; -Examples of suitable algorithms are provided in Figures 5A, 5B and 8; Brake current sensor - Actual current in the brake coil (I BRAKE ) to measure; Brake coil control logic -including various types of closed-loop feedback control methods, such as proportional control (P), proportional-integral control (PI), proportional-integral-derivative control (PID) or other similar methods suitable for closed-loop feedback control; -Brake Command (I COMMAND,BRAKE ) and the measured brake coil current (I BRAKE ) and calculate the duty cycle of the PWM signal that drives the brake coil current amplifier; Brake coil current amplifier -including circuitry that generates a variable current to the brake coil based on an input PWM command; Steering system dynamics - The movement of the steering wheel shaft 18 when the operator tries to turn the steering wheel 16 while a braking torque is applied.

[0014] 1 and 6 present exemplary embodiments of a system architecture for improving the safe operation of a steer-by-wire system. FIG. 1 shows a directional control element 10, e.g., a wheel, of a land vehicle, or a rudder or other similar directional control mechanism in the case of a watercraft. For simplicity, in the remainder of this disclosure, the directional control element 10 will be referred to as a wheel 10. The wheel 10 corresponds to the rudder of a watercraft. The wheel 10 has a rotation angle (θ) that is proportional to the rotation angle of the road vehicle wheel. RWA ) or at least one RWA sensor 12 suitable for monitoring changes in the rudder angle position of the vessel. SPEED ) is measured by a speed sensor 58. A vehicle steering controller 14 manages the operation of a steer-by-wire system installed in the vehicle and receives data from the RWA sensor 12 and the vehicle speed sensor 58. A steering wheel 16 supported by a steering shaft 18 provides steering input from an operator to the steer-by-wire system. In series with the steering shaft 18 is an FFD 20. The FFD 20 includes an electrically controlled brake 22, an electrically controlled motor 24, and at least one angular position sensor 44, 46 configured to monitor the position of the steering shaft 18. The FFD 20 further includes a steering input controller 21, which controls the brake 22 and the motor 24, and the FFD 20 also exchanges information with the vehicle steering controller 14 via a digital communication bus 52. An example of a suitable digital communication bus typically installed in a vehicle is a Controller Area Network (CAN) bus.

[0015] 1, the brake 22, motor 24, and position sensors 44, 46 can be positioned within the same housing. The angular position sensors 44, 46 can be any sensor suitable for monitoring rotational changes of the steering shaft 18, for example, a non-contact Hall Effect sensor providing the ability to read the angular orientation of the magnet 26 attached to the steering shaft 18. The angular position sensors 44, 46 provide data directly to the vehicle steering controller 14 via an electrical bus 62, optionally using analog, PWM, or digital signals (e.g., SPI, SENT).

[0016] Figure 6 differs from Figure 1 in that the motor 24 is located outside of the housing that contains the brake 22 and the sensors 44, 46. However, the sensors 44, 46 are not necessarily attached to or fixed to the shaft 18. Rather, the sensors 44, 46 are mounted in locations suitable for monitoring changes in the radial angle of the magnet 26. Figure 6 therefore demonstrates that the brake 22 and motor 24 may be positioned in alternative configurations relative to the steering shaft 18, so long as they are connected to the steering shaft 18 in a manner sufficient to provide the torque and braking action necessary to achieve the desired torque feedback and return of the steering shaft 18 based on target parameters.

[0017] As shown in FIGS. 2 and 7, angular position sensors 44, 46 provide angular position data of steering shaft 18 to microcontrollers 50, 50a, 50b. In FIG. 2, angular position sensor 44 is comprised of an independent sensor pair S1, S2, while angular position sensor 46 is comprised of an independent sensor pair S3, S4. As shown in FIGS. 1 and 6, brake 22 and motor 24 are mounted in series with and mechanically connected to steering wheel 16 by steering shaft 18. Additionally, if sensors 44, 46 take the form of Hall-effect sensors, steering shaft 18 can support reference magnet 26 as a reference point for sensors 44, 46. As known to those skilled in the art, Hall-effect sensors provide the ability to monitor rotational changes of a magnet by referencing the magnet's poles.

[0018] As shown in detail in FIG. 2 , one embodiment of the FFD 20 has three power inputs 32, 34, and 36. However, in this embodiment, the number of independent power inputs is not critical, as a single power source is sufficient for operation of the FFD 20. Power input 32 provides power to a brake drive amplifier 38, a motor drive amplifier 42, and a microcontroller 50. The brake drive amplifier 38 provides current to the electrically controlled brake 22, and the motor drive amplifier 42 provides current to the electrically controlled motor 24. Power input 34 provides power to a first pair of angular position sensors 44. Power input 36 provides power to a second pair of angular position sensors 46. Optionally, power from power inputs 32, 34, and 36 passes through a power conditioning unit 48, which ensures a smooth, continuous current supply to each component while meeting industry-mandated power input requirements. The power conditioning unit 48 is selected to provide the appropriate current to the device being powered. 2, power input 32 receives battery current from the vehicle's on-board battery, for example, 12 V or 24 V. Power inputs 34, 36 may receive power from the vehicle steering controller 14 at a supply voltage level, for example, 5 V. However, other voltages may be used within the scope of this embodiment depending on the unit receiving the current.

[0019] Continuing with reference to FIG. 2, the FFD 20 includes a magnet 26 supported by the steering shaft 18, a first pair of angular position sensors 44, and an optional second pair of angular position sensors 46 configured to read the orientation of the magnet 26. Additionally, the FFD 20 includes at least one microcontroller 50 in data communication with a controller area network (CAN) 52. The microcontroller 50 receives power from the power input 32 via an optional power conditioning unit 48. The microcontroller 50 is also in data communication with the brake drive amplifier 38, the motor drive amplifier 42, and the first pair of angular position sensors 44. In this embodiment of FIG. 2, the first pair of angular position sensors 44 and the second pair of angular position sensors 46 provide data to the vehicle steering controller 14 during vehicle operation. The inter-functionality of the components is described below.

[0020] The functionality of the exemplary embodiments is described with reference to FIGS. 3-5 and 8. The exemplary embodiments disclosed herein function as a closed-loop system, thereby improving the safety of a steer-by-wire system in a vehicle (not shown) associated with the system architecture. The disclosed system provides controlled feedback to the vehicle operator and operates to return the steering shaft 18 to a target parameter defined by the microcontroller 50. Typically, the target parameter corresponds to a center position of the steering control system. As used herein, the term center position corresponds to a neutral or straight-ahead position of the steering system. The calculation of the target parameter by the microcontroller 50 is based on information transmitted by the vehicle steering controller 14 via the CAN bus 52. The information used to calculate the target parameter may be any one or combination of parameters, such as RWA, vehicle speed, and lateral acceleration. Movement of the steering shaft 18 returning the target parameter to a zero value also causes the steering wheel 16 and road wheels 10 to return to a center position. Additionally, microcontroller 50 manages the operation of both electronically controlled brake 22 and electronically controlled motor 24 by controlling brake drive amplifier 38 and motor drive amplifier 42. Microcontroller 50 therefore prevents unintended operation of motor 24 and steering lock-up caused by unintended current flow through brake drive amplifier 38.

[0021] Sensors providing RWA, vehicle linear velocity, and vehicle lateral acceleration for the vehicle shown in FIG. 1 are well known to those skilled in the art. These sensors, as well as the vehicle steering controller 14, are provided as part of the vehicle's standard equipment. During operation of the land or water vehicle, sensor data from the linear velocity sensor 58 is received by the vehicle steering controller 14. Additionally, the vehicle steering controller 14 receives wheel angle (RWA) data from the RWA sensor 12, vehicle speed (v) from the vehicle speed sensor 58, and vehicle speed (v) from the vehicle steering controller 14. SPEED) and optionally lateral acceleration from lateral acceleration sensor 56. Note that lateral acceleration can be calculated by microcontroller 50 based on other vehicle parameters transmitted by vehicle steering controller 14. Vehicle steering controller 14 then transmits the data to microcontroller 50 of FFD 20 via CAN 52. Note: In the case of a water vehicle, RWA corresponds to the angle of the rudder or other device that provides directional control of the water vehicle, such as the nozzle of a jet ski. For the remainder of this disclosure, the description will simply refer to RWA.

[0022] The vehicle steering controller 14 initiates diagnostic logic that detects one or more sensor failures when analyzing raw sensor data from both pairs of angular position sensors 44, 46, the linear velocity sensor 58, the optional lateral acceleration sensor 56, and the RWA sensor 12. The lateral acceleration sensor 56 may be omitted because lateral acceleration can be estimated using other sensor measurements. In this manner, the vehicle steering controller 14 receives data regarding vehicle dynamics and determines whether the sensors are functioning properly. If one or more sensor failures are detected, the vehicle steering controller 14 determines the safety state of the vehicle.

[0023] Examples of safe states include an immediate stop of the vehicle, a return to an alternate steering input system, or a switch to a low-speed "limp-home" mode. The nature of the safe state is typically determined by the vehicle's integrated systems and is subject to a risk analysis of the vehicle's functional safety. Typically, the safe state is selected to prevent operator injury by disabling the system upon an indicated fault. Additionally, the microcontroller 50 performs diagnostic checks of the sensor data provided by both pairs of angular position sensors 44, 46.

[0024] Providing data to the microcontroller 50 initiates the closed-loop operation shown in Figures 3A and 3B. During operation of either a land or water vehicle equipped with a steer-by-wire system, movement of the steering shaft 18 (box A) results in a change in the angular position of the magnet 26, which is read by the angular position sensors 44, 46 (box B). Data from the angular position sensors 44, 46 is reported by the microcontroller 50 to the vehicle steering controller 14 (box D) via any convenient path, such as the CAN 52, or using an electrical signal 62, such as a pulse-width modulated signal, or an analog voltage level via another connection (box C). Using this input sensor data, the vehicle steering controller 14 provides the vehicle steer-by-wire system with the orientation (θ RWA At the same time, the vehicle steering controller 14 (Box D) receives one or more combinations of linear velocity and lateral acceleration data from the vehicle's original equipment sensors 12, 56, 58.

[0025] Data from the vehicle steering controller 14 is passed via CAN 52 to the microcontroller 50 (Box E) of the FFD 20. The microcontroller 50 (Box E) uses the data to calculate target parameters, then performs data scaling and saturation (Box F), as defined above and known to those skilled in the art, to improve the operation of the microcontroller 50. Note: Each vehicle's response is different (based on weight, wheel configuration, steering ratio, turning actuation method, road conditions, etc.). Therefore, it is impossible to accurately model all vehicles and all situations. However, the closed-loop control strategy shown in Figures 3A and 3B provides the ability to provide desired performance while addressing all vehicle types and the inherent parameter variations of various vehicles.

[0026] As shown in FIGS. 3A and 3B, the target parameter is used as a feedback input to determine the value required for operation of the electric control motor 24 and to enhance safe control of the steer-by-wire system to command motor torque that drives the target parameter value to zero. The microcontroller 50 manages operation of the motor 24 in a manner that drives the target parameter value to zero, thereby maneuvering the steering shaft 18 to a defined center position. Additionally, damping of the steering shaft 18 is achieved by operation of the brake 22 by the microcontroller 50. This damping action slows the motion of the steering shaft 18, thereby minimizing oscillations up and down the target parameter. In other words, operation of the brake 22 provides resistance to changes in the angular position of the steering shaft 18. In this way, the FFD 20 replicates the return-to-center behavior of a conventional mechanical system.

[0027] 3, the microcontroller 50 performs all steps in boxes H, I, J, and K of the control feedback portion of the closed loop operation shown in primary box G. The microcontroller 50 is programmed with a suitable closed loop feedback control scheme such as, but not limited to, proportional control (P), proportional integral control (PI), or proportional integral derivative control (PID). The initial output of the closed loop feedback is the desired motor torque T COMMAND The microcontroller determines the T COMMAND Using the value of , and the known motor torque constant (Box I), this determines the current I required to govern the operation of the motor drive amplifier 42 that controls the motor 24. COMMAND is determined. COMMAND Using the values ​​of , the microcontroller 50 applies the required current (box K) to the windings of the motor 24, thereby generating the motor torque T required to achieve the target parameters by rotating the steering shaft 18 to the desired position. STEER(Box N) is generated. Microcontroller 50 constantly monitors and performs diagnostics on electrically controlled motor 24 (Box J) using data from motor current amplifier 42 (Box L) and motor current sensor (Box M). Finally, under the direction of microcontroller 50, motor current (Box K) is passed to motor current amplifier 42 (Box L) and applied to electrically controlled motor 24, thereby achieving the desired feedback, i.e., torque applied to steering shaft 18, for safe operation of the steer-by-wire system.

[0028] Thus, microcontroller 50 utilizes vehicle steering controller 14 data, i.e., RWA, lateral acceleration, and linear velocity, as well as the angular position of the steering shaft measured by at least one of first angular position sensor pair 44 and second angular position sensor pair 46, to manage electric motor 24 and electric brake 22 to provide the torque required to return steering shaft 18 to a center position corresponding to the target parameters. FFD system 20 thus works in conjunction with vehicle steering controller 14 to simulate the mechanical motion provided by the vehicle's suspension alignment (specifically, caster and toe-in values ​​in a conventional land vehicle).

[0029] 4A and 4B show a flowchart of the safety loop controlling the operation of the electrically controlled motor 24. The process flow steps outlined in FIG. 4 prevent unintended operation of the motor drive amplifier 42, which could result in unintended operation of the electrically controlled motor 24. The process begins with the FFD microcontroller 50 or FFD microcontroller 50a reading vehicle information transmitted to the FFD microcontroller 50 or FFD microcontroller 50a via the CAN bus 52. The microcontroller 50 or FFD microcontroller 50a then calculates the desired motor torque required to rotate the shaft. The microcontroller then reads values ​​from the angular position sensors 44, 46 to determine if any of the sensors are faulty. If a persistent fault exists, the microcontroller disables the motor drive circuitry. If no sensor faults exist, the microcontroller calculates the motor winding current required for commutation and controls the motor drive amplifier circuitry accordingly. The microcontroller then reads the motor current sensors and calculates the error between the command level and the actual. If the error persists beyond a predetermined tolerance, the counter is incremented; if it does not, the counter is reset to zero. If the error persistence counter exceeds a certain safety limit, the microcontroller disables the motor drive amplifier circuit and sets appropriate motor current fault parameters. These preset safety limits typically correspond to the response time of a human operator or the response time of the vehicle steering controller 14. If the value of the motor current tracking error counter is below the acceptable safety limit, the motor drive circuit remains enabled. One effect of disabling the motor drive circuit is that the command current level is set to zero. This software operation provides one approach to disabling the drive circuit.

[0030] Finally, the microcontroller includes the motor current fault parameters in a CAN message and transmits it on the CAN bus 52. As shown in Figures 4A and 4B, during operation of the electrically controlled motor 24, the microcontroller 50 monitors the current to and from the motor drive amplifier 42. If the current applied to the electrically controlled motor 24 falls outside of predetermined specifications for a predetermined duration programmed into the microcontroller 50, the microcontroller 50 disables the motor drive amplifier 42. Thus, the microcontroller 50 prevents unintended motor operating conditions that may result from a failure of the motor drive amplifier 42.

[0031] 5A and 5B present a flowchart of the safety loop that controls the operation of the electrically controlled brake 22. The process flow steps outlined in FIGS. 5A and 5B prevent unintended operation of the brake drive electronics 38, which could lead to excessive torque or a locked steering shaft 18 condition. The process begins with the FFD microcontroller 50 or FFD microcontroller 50a reading vehicle information transmitted to the FFD microcontroller 50 or FFD microcontroller 50a via the CAN bus 52. The microcontroller then reads values ​​from the angular position sensors 44 and 46 to determine whether any of the sensors are faulty. If a persistent fault exists, the microcontroller disables the brake drive circuit. If no sensor faults are determined, the microcontroller uses the angle sensor values ​​to calculate the steering position and velocity, and subsequently calculates the current required to generate brake feel. The microcontroller then commands current to flow through the brake coils. The microcontroller then reads the actual current in the brake coils using the brake current sensors and calculates the tracking error between the commanded current level and the actual sensed current level. If the error persists beyond a predetermined tolerance, a counter is incremented. When the error is eliminated, the counter is reset to zero. If the error persistence counter exceeds a certain safety limit, the microcontroller disables the brake drive amplifier circuit and sets the appropriate brake current fault parameters. If the value of the brake current tracking error counter is below the acceptable safety limit, the brake drive circuit remains enabled. One effect of disabling the brake drive circuit is to set the command brake current level to zero. Finally, the microcontroller includes the brake current fault parameters in a CAN message and transmits it on the CAN bus 52.

[0032] During the closed-loop operation shown in FIGS. 3A and 3B , the vehicle steering controller 14 and microcontroller 50 also continuously perform diagnostic checks on the first angular position sensor 44 and, optionally, in some embodiments, on the angular position sensor 46, the brake drive amplifier 38, and the motor drive amplifier 42. In the exemplary embodiment of FIGS. 1 and 2 , the vehicle steering controller 14 is primarily responsible for monitoring conventional on-board sensors, such as linear and lateral velocity sensors (not shown) and the first and second angular position sensor pairs 44 and 46. Data from these sensors is transmitted to the vehicle steering controller 14, as described above. If the microcontroller 50 detects a persistent fault in one or more of the angular position sensors 44, 46, it disables the motor drive amplifier 42 and disables the brake drive amplifier 38. Thus, while FIGS. 4A and 4B provide safety-loop operational control for the electrically controlled motor 24, FIGS. 5A and 5B provide safety-loop operational control for the electrically controlled brake 22.

[0033] In addition to monitoring the indicated sensors by the vehicle steering controller 14, the microcontroller 50 monitors the current to and from the brake drive amplifier 38. If the current applied to the electrically controlled brakes 22 falls outside predetermined specifications for a predetermined duration programmed into the microcontroller 50, the microcontroller 50 will shut down the brake drive amplifier 38. Thus, the microcontroller 50 prevents a steering lock condition that may result from a failure of the brake drive amplifier 38.

[0034] 7 presents a second exemplary embodiment of a block diagram of the components of the FFD 20. This exemplary embodiment differs from the embodiment shown in FIG. 2 in that the angular positions measured by the sensors 44, 46 are read by the FFD microcontrollers 50a, 50b and then transmitted to the vehicle steering controller 14 via the CAN bus 52. In this embodiment, there is no direct electrical communication between the angle sensors 44, 46 and the vehicle steering controller 14. Additionally, sensor diagnostics for both angular position sensor pairs 44, 46 are initially performed by the microcontrollers 50a, 50b and provided to the vehicle steering controller 14 via the CAN bus 52. The microcontrollers 50a, 50b digitally communicate with each other via an electrically isolated interface 54 and also communicate with the angular position sensors 44, 46 and the motor current control (I COMMAND , Fig. 3b) and brake current control (I COMMAND-Brake, 8). In the embodiment of FIGS. 6 and 7, only two power inputs 32, 34 are required. Input 32 provides power to the main microcontroller 50a, the first angular position sensor 44, the brake drive amplifier 38, and the motor drive amplifier 42. Input 34 provides power to the safety microcontroller 50b and the second angular position sensor 46. The safety microcontroller 50b also communicates with the vehicle steering controller 14, providing sufficient redundancy to allow a "limp home" mode of operation in the event of a failure of the main microcontroller 50a. The main microcontroller 50a has primary control over the operation of the brake drive amplifier 38 and the motor drive circuit 42, and can shut down both if a persistent fault is detected according to the flowcharts of FIGS. 4 and 5. The safety microcontroller 50b monitors the status of the brake drive amplifier 38 and the motor drive circuit 42 and can independently shut down both if a persistent fault is detected. The operation of the exemplary embodiment of FIGS. 6 and 7 uses the same programming illustrated in the process flow diagrams of FIGS. 3-5 as the programming used by the exemplary embodiment of FIGS. 1 and 2.

[0035] 8 illustrates the closed-loop operation of the haptic feel generated by the electrically actuated brake 22. The haptic feel is based on the operator's desired feedback and can include features such as end stops, intermediate speed dependent braking, or warning vibrations. The braking torque T generated by the electrically actuated brake 22 is BRAKE (Box A) acts on the steering system (Box B) and provides haptic feedback or braking resistance to the operator of the steering wheel 16. The resulting steering movement (θ STEER ) is read by the angular position sensors 44, 46 (box C) and used by the main microcontroller 50 or main microcontroller 50a to generate the brake current command I to obtain the desired brake feel. COMMAND-Brake(Box D) is calculated. Next, the microcontroller 50 or microcontroller 50a calculates the brake coil current I measured by the brake current sensor (Box I) in response to this command. BRAKE and calculate the required PWM amplifier duty cycle (box F). The brake drive amplifier (box H) applies current to the brake 22 to perform the braking action (box A). The microcontrollers 50, 50a, 50b also monitor the coil sensors and the angular position sensors (box G) and can shut down the brake current amplifier if a fault is detected.

[0036] Other embodiments of the present invention will be apparent to those skilled in the art. Accordingly, the above description merely enables and describes the general application and method of the present invention. The true scope of the present invention is therefore defined by the following claims.

Claims

1. 1. A force feedback system comprising: a steering shaft 18; a hall sensor magnet 26 supported on the steering shaft; an electrically controlled brake 22 configured to engage the steering shaft; an electronically controlled motor 24 configured to engage the steering shaft; at least one power source 32; a brake drive amplifier 38 that receives power from the at least one power source and provides current to the electronically controlled brake; a motor drive amplifier 42 that receives power from the at least one power source and provides current to the electronically controlled motor; a first pair of angular position sensors 44 receiving power from the at least one power source; a vehicle controller in data communication with the first pair of angular position sensors; A force feedback system comprising:

2. The force feedback system of claim 1 , wherein the first pair of angular position sensors is positioned to monitor radial displacement of the Hall sensor magnet.

3. the force feedback system further comprising a second pair of angular position sensors, the second pair of angular position sensors receiving power from the at least one power source; the first pair of angular position sensors and the second pair of angular position sensors are positioned to monitor radial displacement of the Hall sensor magnet; The force feedback system of claim 1 .

4. 2. The force feedback system of claim 1, further comprising a microcontroller in data communication with the vehicle controller, the first pair of angular position sensors, the brake drive amplifier, and the motor drive amplifier, the microcontroller receiving power from the at least one power source.

5. 5. The force feedback system of claim 4, wherein the microcontroller is programmed to receive vehicle data via a digital communication bus and to control the electronically controlled motor and the electronically controlled brake in response to the received vehicle data.

6. 5. The force feedback system of claim 4, further comprising a second power supply, wherein the first power supply provides power to the microcontroller, the brake drive amplifier, and the motor drive amplifier, and the second power supply provides power to the first pair of angular position sensors and the second pair of angular position sensors.

7. 5. The force feedback system of claim 4, further comprising a second power supply and a third power supply, wherein the first power supply provides power to the microcontroller, the brake drive amplifier, and the motor drive amplifier, the second power supply provides power to the first pair of angular position sensors, and the third power supply provides power to the second pair of angular position sensors.

8. 1. A force feedback system comprising: a steering shaft 18; a hall sensor magnet 26 supported on the steering shaft; an electrically controlled brake 22 configured to engage the steering shaft; an electronically controlled motor 24 configured to engage the steering shaft; a first power source 32; a second power source 34; and a third power source 36; and a brake drive amplifier 38 that receives power from one of the first power sources and provides current to the electronically controlled brake; a motor drive amplifier 42 that receives power from the first power supply and provides current to the electronically controlled motor; a first pair of angular position sensors 44 receiving power from at least one power source and further receiving power from the second power source; a second pair of angular position sensors 46 receiving power from at least one power source and further receiving power from said third power source; a vehicle controller in data communication with the first pair of angular position sensors and the second pair of angular position sensors; A force feedback system comprising:

9. 9. The force feedback system of claim 8, wherein the first pair of angular position sensors and the second pair of angular position sensors are positioned to monitor radial displacement of the Hall sensor magnet.

10. 9. The force feedback system of claim 8, further comprising a microcontroller in data communication with the vehicle controller, the first pair of angular position sensors, the brake drive amplifier, and the motor drive amplifier, the microcontroller receiving power from the at least one power source.

11. 11. The force feedback system of claim 10, wherein the microcontroller is programmed to receive vehicle data via a digital communication bus and to control the electronically controlled motor and the electronically controlled brake in response to the received vehicle data.

12. 1. A force feedback system comprising: a steering shaft 18; a hall sensor magnet 26 supported on the steering shaft; an electrically controlled brake 22 configured to engage the steering shaft; an electronically controlled motor 24 configured to engage the steering shaft; a first power source 32; a brake drive amplifier 38 that receives power from the first power source and provides current to the electronically controlled brake; a motor drive amplifier 42 that receives power from the first power supply and provides current to an electronically controlled motor; a first pair of angular position sensors 44 receiving power from the first power source; a vehicle controller 14; A main microcontroller 50a and a safety microcontroller 50b A force feedback system comprising:

13. 13. The force feedback system of claim 12, wherein the force feedback system further comprises a vehicle steering controller 14, the vehicle steering controller in data communication with the main microcontroller and the safety microcontroller, the main microcontroller receiving data communications from the brake drive amplifier, the motor drive amplifier and the first pair of angular position sensors, and the vehicle steering controller not in direct electrical communication with the first pair of angular position sensors.

14. 13. The force feedback system of claim 12, wherein the first pair of angular position sensors are positioned to monitor radial displacement of the Hall sensor magnet.

15. the force feedback system further comprising a second pair of angular position sensors, the second pair of angular position sensors receiving power from at least one power source; the first pair of angular position sensors and the second pair of angular position sensors are positioned to monitor radial displacement of the Hall sensor magnet; 13. The force feedback system of claim 12.

16. 13. The force feedback system of claim 12, wherein the main microcontroller is programmed to control the electronically controlled motor and the electronically controlled brake in response to vehicle data received from the vehicle controller and in response to data received from the first pair of angular position sensors and the second pair of angular position sensors.

17. the force feedback system further comprising a second power source; the first power supply powers the main microcontroller, the brake drive amplifier, the motor drive amplifier, and the first pair of angular position sensors; the second power supply powers the second pair of angular position sensors and the safety microcontroller; 13. The force feedback system of claim 12.

18. 13. The force feedback system of claim 12, wherein the safety microcontroller is in data communication with the main microcontroller, the brake drive amplifier, the motor drive amplifier, the vehicle controller, the first pair of angular position sensors, and the second pair of angular position sensors.

19. 13. The force feedback system of claim 12, wherein the safety microcontroller is programmed to disable the electronically controlled motor and disable the electronically controlled brake in the event of a failure of the main microcontroller.

20. 1. A method for returning a steering control system of a vehicle to a center position, comprising: the vehicle having at least one steering wheel capable of adjusting the steering control system over a range of angular orientations that includes a center position of the steering control system; the steering control system includes an electric motor 24 and a steering input controller 21, the steering input controller controlling the operation of the electric motor to directly or indirectly control the wheel angle; the steering control system includes a force feedback device (20), the force feedback device being in data communication with the vehicle steering controller, the force feedback device including at least one angular position sensor (44), an electric motor (24), an electrically actuated brake, and a microcontroller (50); The method comprises: transmitting data provided by the at least one angular position sensor to a vehicle controller; transmitting data from wheel angle sensors and vehicle speed sensors to the vehicle controller; analyzing, by the vehicle controller, the received data to thereby detect a fault in any one of the at least one angular position sensor; initiating a closed loop operation by the microcontroller to effect a change in angular orientation of the wheel; defining, by the microcontroller, a value for a target parameter using the data received by the microcontroller, wherein a zero value corresponds to a center position of a steering control of the vehicle; managing operation of the force feedback system with the microcontroller, thereby driving a target parameter to a zero value by controlling operation of the electric motor; A method comprising:

21. the force feedback system further comprising a steering shaft connected to the steering wheel, the steering shaft operatively connected to the electric motor and to an electric brake, operation of the electric brake being managed by the microcontroller; The method further comprises: calculating, by the microcontroller, a torque value that the electric motor applies to the steering shaft; controlling operation of the electric brake with the microcontroller to thereby provide resistance to changes in the angular position of the steering shaft; 21. The method of claim 20, comprising:

22. the force feedback system further comprising a motor drive amplifier; The method further comprises: monitoring, by the microcontroller, a current applied to the electric motor, the microcontroller being programmed with an allowable current range for operation of the electric motor; disabling, by the microcontroller, the motor drive amplifier when the current applied to the electric motor falls outside the allowed current range for a predetermined duration; transmitting, by the microcontroller, motor fault information to the vehicle controller via a digital communication bus; 22. The method of claim 21, comprising:

23. the force feedback system further comprising a brake drive amplifier; The method further comprises: monitoring, by the microcontroller, a current applied to the electric brake, the microcontroller being programmed with an allowable current range for operation of the electric brake; disabling, by the microcontroller, the brake drive amplifier when the current applied to the electric brake is outside the allowed current range for a predetermined duration; transmitting, by the microcontroller, motor fault information to the vehicle controller via a digital communication bus; 22. The method of claim 21, comprising:

24. 22. The method of claim 21, further comprising disabling the electric motor and the electric brake when a fault is detected in any one of the at least one angular position sensor.

25. 25. The method of claim 24, further comprising transmitting sensor fault information to the vehicle controller via the digital communication bus.

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