The present invention relates to a control system for a steering system, and more particularly to a control system for determining a rejection command based on hand wheel acceleration and road wheel frequency.
Vehicles are subjected to some degree of disturbance in the front road wheels. In one example, road wheel disturbance may be caused by variations in brake disk thickness, which is referred to as brake judder. The variation in brake disk thickness may create a harmonic modulation of a braking force during braking of the vehicle, which in turn may be transmitted to a steering column and a hand wheel of a steering system. The vibrations created in the hand wheel may be detected by a driver. Some approaches currently exist for reducing and rejecting road wheel disturbance. However, while they might be relatively effective at rejecting road wheel disturbance at higher vehicle speeds, these approaches may not be as effective if the vehicle is operating at relatively lower vehicle speeds. In other examples, road wheel disturbances may also be caused by imbalance, tire non-uniformity, or brake disk thermal effects.
In one embodiment, a control system for a steering system is provided, and includes an acceleration module, a scaling module, and a final command module. The acceleration module determines hand wheel acceleration. The scaling module determines a rejection command. The rejection command is based on the hand wheel acceleration and a road wheel frequency. The final command module determines an adjusted assist command that is based on a normal assist command and the rejection command.
In another embodiment, a method for determining a rejection command for a steering system is provided. The method includes determining hand wheel acceleration by an acceleration module. The method includes determining the rejection command by a scaling module. The rejection command is based on the hand wheel acceleration. The method includes sending an adjusted assist command that is based on a normal assist command and the rejection command to a motor by a final command module.
In yet another embodiment, a control system for a steering system is provided, and includes an acceleration module, a scaling module, and a final command module. The acceleration module determines hand wheel acceleration. The hand wheel acceleration is based on an extended state observer, and is determined based on a motor torque command, a hand wheel torque, a motor position, and a motor velocity. The scaling module determines a rejection command. The rejection command is based on the hand wheel acceleration and a road wheel frequency, and represents a road wheel disturbance cancel amount. The final command module determines an adjusted assist command that is based on a normal assist command and the rejection command.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, an exemplary embodiment of a vehicle 10 including a steering system 12 is illustrated. In various embodiments, the steering system 12 includes a handwheel 14 coupled to a steering shaft 16. In the exemplary embodiment shown, the steering system 12 is an electric power steering (EPS) system that further includes a steering assist unit 18 that couples to the steering shaft 16 of the steering system 12 and to a left tie rod 20 and a right tie rod 22 of the vehicle 10. It should be noted that the steering system 12 may be a rack assist EPS (REPS) as well. The steering assist unit 18 includes, for example, a rack and pinion steering mechanism (not shown) that may be coupled through the steering shaft 16 to a steering actuator motor and gearing. During operation, as the handwheel 14 is turned by a vehicle operator, the motor of the steering assist unit 18 provides the assistance to move the left tie rod 20 and the right tie rod 22 which in turn moves left and right steering knuckles 24, 26, respectively. The left knuckle 28 is coupled to a left roadway wheel 28, and the right knuckle 26 is coupled to a right roadway wheel 30 of the vehicle 10.
As shown in
A control module 50 controls the operation of the steering system 12 based on one or more of the sensor signals and further based on the steering control systems and methods of the present disclosure. Referring now to
The control module 50 determines a rejection command 52. The rejection command 52 represents a road wheel disturbance cancel amount based on the velocity of the road wheels (e.g., the left wheel 28 and the right wheel 30 shown in
In the exemplary embodiment as shown, the control module 50 receives as input a motor torque command 70, a hand wheel torque 72, a motor position 74, a motor velocity 76, a left wheel speed 77 that is converted into a left wheel frequency 78, a right wheel speed 79 that is converted into a right wheel frequency 80, brake pressure 82, and a position authority signal 84. The control module 50 (or another module) may convert the motor torque command 70 from motor coordinates into steering coordinates (e.g., motor Nm to hand wheel Nm) by scaling the motor torque command 70 by a motor-to-steering wheel ratio. In one embodiment, the motor torque command 70 may represent a final command sent to a motor of the steering assist unit 18 shown in
The hand wheel torque 72 is measured by the torque sensor 36 shown in
The left wheel frequency 78 may be determined based on the left wheel speed 77 and the right wheel frequency 80 may be determined based on the right wheel speed 79. The left wheel speed 77 is determined by the left wheel speed sensor 32 and the right wheel speed is determined by the right wheel speed sensor 34 shown in
The brake pressure 82 may be determined, for example, by monitoring a vehicle controller area network (CAN) bus. The brake pressure 82 represents the braking pressure as applied by a driver. The position authority signal 84 is a unitless signal that varies from 0 to 1, and represents an amount of confidence that the motor position 74 at initialization is generally accurate.
The control module 50 generally performs two different functions, determining an acceleration estimation 90 of the hand wheel 14 (
In one exemplary embodiment, the acceleration module 54 may determine the acceleration estimation 90 using an extended state observer, which is described below. However, it is to be understood that other approaches may be used as well to determine the acceleration estimation 90. In one embodiment, acceleration of the hand wheel 14 (
{circumflex over ({dot over (x)})}obs=Aobs{circumflex over (x)}obs+Bobsu+L(y−ŷ) Equation 1
where the cap or hat symbol “^” is used to indicate an estimated signal (e.g., a calculated or predicted system output), and the subscript “obs” indicates observed. Specifically, xobs refers to a state of the steering system 12, and contains state variables that represent values inside the steering system 12. The term {circumflex over (x)}obs refers to a calculated state of the steering system 12. The term {circumflex over ({dot over (x)})}obs represents the rate of change of the system state, or a state change (e.g., the differentiation of {circumflex over (x)}obs). The term u refers to system input. The term y refers to system output. The term Aobs refers to a system matrix, and determines how the current state (e.g., {circumflex over (x)}obs) affects the state change {circumflex over ({dot over (x)})}obs. The term Bobs represents a control matrix, and determines how the system input u affects the state change {circumflex over ({dot over (x)})}obs. L represents the observer gain matrix, and determines how an error e between a measured system output y and a calculated system output ŷ affects the state change {circumflex over ({dot over (x)})}obs. Finally, the term Cobs (not expressed in equation 1) refers to an output matrix, and calculates system output ŷ using the calculated state {circumflex over (x)}obs.
The acceleration module 54 receives as inputs the motor torque command 70, the hand wheel torque 72, the motor position 74, and the motor velocity 76. The acceleration module 54 assumes an accurate motor position 74 to correctly determine the acceleration estimation 90. The hand wheel torque 72 may be scaled by 1/tb_K to determine a t-bar angle, where tb_K represents a t-bar stiffness of the torque sensor 36 (
The motor torque command 70 is scaled by the control matrix Bobs and sent to the summation block 92, and the calculated state {circumflex over (x)}obs is sent to the summation block 92 as well. The error term, e, multiplied with the observer gain, L, is also sent to the summation block 92. The summation block 92 outputs the state change {circumflex over ({dot over (x)})}obs. The state change {circumflex over ({dot over (x)})}obs is sent to an integrator 94. The integrator 94 provides an estimate of the states (i.e., the calculated state {circumflex over (x)}obs). The state change {circumflex over ({dot over (x)})}obs may be scaled by a vector value P in order to determine the acceleration estimation 90. The vector P is used to extract a rate of change of velocity (e.g., the acceleration) that is coming out of the summation block 92.
Referring back to
Referring now to
Referring back to
The scale module 60 receives as input the adjusted filtered hand wheel acceleration 120 from the phase adjust module 58, the average center wheel frequency 98, the hand wheel torque 72, brake pressure 82, and the position authority signal 84. The scale module 60 requires the position authority signal 84 in order to correctly determine the rejection command 52. The scale module 60 uses a scale function to provide gain based on the average center wheel frequency 98, the hand wheel torque 72, and brake pressure 82. The scale module determines the rejection command 52.
The hand wheel torque 72 is sent to a hand wheel torque scale 130, which is shown in greater detail in
Turning back to
Turning back to
Referring now to
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, 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 seen as limited by the foregoing description.
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