Yaw damper for two-wheel self-balancing vehicles.

Abstract

A control path is added to a two-wheel self-balancing vehicle with CMG or reaction wheel actuators for steering augmentation and roll balance. These actuators are used to damp yaw disturbances while preventing roll disturbances based on the yaw rate disturbance signal received on the control path.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This U.S. patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 181,795, the disclosure of which is incorporated herein by reference in its entirety. This U.S. patent application is a related U.S. patent application Ser. No. 16 / 085,975, entitled "Control of a Two-Wheeled Self-Balancing Vehicle," filed Sep. 17, 2018, the disclosure of which is incorporated herein by reference in its entirety. This U.S. patent application is a related U.S. patent application Ser. No. 16 / 499,833, entitled "Augmented Tire Traction System for Two-Wheeled Vehicle," filed Sep. 30, 2019, the disclosure of which is incorporated herein by reference in its entirety. This U.S. patent application is a related application to U.S. patent application Ser. No. 16 / 979,094, entitled “Integrated Control Method for Balancing a Two-Wheeled Vehicle Using Control Moment Gyroscopes and Drive-by-Wire Steering Systems,” filed Sep. 8, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0002] (Technical field) The present invention relates to a two-wheel self-balancing vehicle, and more particularly to the damping of yaw disturbances in a two-wheel self-balancing vehicle. [Background technology]

[0003] A two-wheel self-balancing vehicle has two sets of actuators used to balance the vehicle. The primary actuator is a control moment gyro (CMG). The CMG applies torque on the roll axis ("roll axis torque", or simply "roll torque") to balance the vehicle. The second actuator augments the steering. By adding or subtracting torque from the driver-commanded steering, the second actuator provides additional roll torque that increases the driving range of the vehicle. The augmented steering actuator changes the steering angle, and therefore the yaw rate of the two-wheel self-balancing vehicle, and the subsequent value of the centrifugal force. The centrifugal force acts on the center of gravity of the vehicle, producing a change in the roll axis torque. These two actuators work together to produce the desired roll axis torque when balancing a two-wheel self-balancing vehicle. They can also act to counteract the total roll torque while affecting the yaw rate of the vehicle.

[0004] Two-wheeled vehicles can have poorly damped vibration modes in the yaw direction, sometimes called wobble and / or weave. This is due to the absence of a chassis damper that can correct the torsional modes about the yaw axis. The primary damping comes from the horizontal spring-damper characteristics of the tires. The chassis spring rate also contributes to the yaw vibrations, but the resulting disturbances are poorly damped. Typically, vehicle designers have very limited options for the horizontal spring rate and damping of tires. Tires are primarily selected for longitudinal road handling performance. [Brief description of the drawings]

[0005] The detailed description is now described with reference to the accompanying drawings, in which the left-most digit of a reference number identifies the figure in which the reference number first appears. Use of the same reference number in different figures indicates similar or identical items or features.

[0006] [Figure 1A] 1 is a graph of Mu, μ, which is the ratio of the magnitude of the horizontal force to the magnitude of the downforce. [Figure 1B] 1 is a graph of a yaw disturbance illustrating that the tire reaction force to the yaw disturbance is out of phase; [Diagram 2] 1 is a graph of yaw rate showing that as a vehicle accelerates from rest to 30 km / h, the yaw rate starts at zero and increases to 1.5 degrees per second. [Diagram 3] 13 is a graph of a bandpass filter applied to the full yaw rate signal to capture disturbance signals. [Figure 4] 4 is a graph showing yaw rate and filter response before applying yaw damper control. [Diagram 5] 1 is a graph showing that yaw disturbance has little effect on the roll rate of a two-wheel self-balancing vehicle. [Figure 6] FIG. 2 is a block diagram of a yaw damper control using a measured yaw rate obtained from an inertial measurement unit (IMU) as a control signal in accordance with an embodiment of the present invention. [Figure 7] FIG. 13 illustrates the application of yaw damper control to steering only to reduce yaw disturbances in accordance with an embodiment of the present invention. [Figure 8] 13 is a graph showing roll disturbance in an embodiment that does not utilize a CMG and therefore is only steering controlled. [Figure 9] 11 is a graph showing roll rate with yaw disturbance frequency removed after adding CMG compensation results according to an embodiment of the present invention. [Figure 10] FIG. 1 is a block diagram of an embodiment of the invention without a CMG where the secondary control path utilizes only steering to maintain balance and has active tuning to achieve yaw damping while compensating for variations in natural frequency due to changing vehicle characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] As mentioned above, the two-wheel self-balancing vehicle has two actuators that generate roll torque: the CMG and the stability augmentation steering actuator, which when used in conjunction provide a mechanism for enhancing yaw damping without affecting the roll torque applied to the vehicle, in accordance with an embodiment of the present invention.

[0008] (theory) For the steady-state rotational torque about the roll axis due to the steering angle of the front wheels, P is the wheelbase of the vehicle and ψ is the steering angle of the wheels.

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[0009] X is the vehicle's position in the direction of travel.

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[0010] M is the mass of the vehicle.

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[0011] Centrifugal force reacts with tire contact force to generate torque.

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[0012] The torque generated by the front wheels and the change in ψ can be countered by the torque provided by the CMG.

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[0013] EXEMPLARY EMBODIMENTS Starting with a model of a two-wheeled self-balancing vehicle, the steering wheel is set to achieve a turn rate of 1.5 degrees per second at 30 km / h. The vehicle starts from rest and accelerates to 30 km / h, which begins at 2.5 seconds. At 7 seconds, a yaw disturbance 102 is present. Mu, μ, shown in graph 100 of FIG. 1A, is the ratio of the magnitude of the horizontal force to the magnitude of the downforce. The maximum limit of Mu is governed by the coefficient of friction between the respective front tires 105 and rear tires 110 and the roadway. In this example, the Mu of the tires is offset from zero by moving in a circular path. This makes it easier to visualize the effects of the yaw disturbance, but the yaw damper control according to an embodiment of the present invention is effective in damping the yaw disturbance no matter which path is assumed. The yaw disturbance 102 is highlighted in graph 100 of FIG. 1B, showing that the tire reaction force is out of phase with the yaw disturbance.

[0014] Graph 200 of FIG. 2 depicts a yaw rate 202 starting at zero and rising to 1.5 degrees per second as the vehicle accelerates from rest to 30 km / h. The value of yaw rate 202 is disturbed by a yaw impulse induced by the road surface, depicted at 204. The yaw disturbance 204 can be felt at the steering wheel due to the fluctuations in steering torque caused by centrifugal acceleration and caster of the steering wheel. The steering wheel in this example is the front wheel, but in some embodiments, the steering wheel could be the rear wheel or both wheels. Most production motorcycles incorporate a mechanical damper somewhere in the steering system due to this phenomenon. Yaw damper control, according to an embodiment of the present invention, utilizes a CMG and steering actuator to augment or completely replace the mechanical damper in the steering system to manage this phenomenon.

[0015] Yaw damper control according to embodiments of the present invention utilizes a yaw rate signal at the natural frequency of the yaw resonance. In some embodiments, a bandpass filter 302 is applied to the full yaw rate signal to capture the disturbance signal 304, as depicted in graph 300 of Figure 3. Graph 400 of Figure 4 depicts the yaw rate 402 and the filter response 404 before applying the yaw damper control.

[0016] As shown in graph 500 of FIG. 5, the yaw disturbance has little effect on the roll rate 502 of the two-wheel self-balancing vehicle or on the ability of balance control to perform correctly. The beginning of the plot depicted at 504 shows the rate sensor being turned on (0.033 seconds). This initiates the roll sensor offset calibration. At 0.75 seconds, the driver commands the vehicle to lift off the landing gear from a 4 degree angle, depicted at 506. 2.4 seconds later, depicted at 508, the vehicle starts and accelerates to 30 km / h, running in a circle which will generate a yaw rate of 1.5 degrees per second. This creates a ramp in the roll rate between 2.8 seconds and 5 seconds as the vehicle rolls to maintain balance due to the changing rate of turn and speed, depicted at 510. At 7 seconds, a yaw disturbance is introduced, depicted at 512.

[0017] In one embodiment, as shown in block diagram 600 of FIG. 6, the yaw damper control uses the measured yaw rate obtained from an inertial measurement unit (IMU) 602 as the control signal. The control block diagram is simple with the addition of a secondary control path to reduce yaw resonance disturbances using the most common sensors and actuators in vehicle balance control. The yaw rate measured by the IMU is passed through a notch filter 604 to isolate yaw disturbances at the vehicle's natural yaw frequency. It is understood that in other embodiments, a different set of sensors can be used to generate the yaw signal, such as differential accelerometers at the front and rear of the vehicle, steering angle feedback, steering actuator force measurements, etc. The notch filter 604 with its inherent phase shift can be designed for fixed conditions that are built into the control, or it can be a self-tuning filter to allow for variations in vehicle dynamics due to age, tire pressure, etc. The gain 606 varies as the inverse of the vehicle speed, and the result is output at 608 as a command to the augmented steering actuator 610. The gain variation is useful because the yaw torque generated by steering increases as the square of the velocity. The same signal is passed through a filter 612 which changes the phase of the signal to compensate for differences in the response of the steering actuator, the CMG gimbal actuator, and the phase lag of the tire dynamics. The gain 614 varies as the square of the velocity because the roll torque due to steering is proportional to the square of the velocity and the torque generated by the CMG is proportional to the CMG gimbal rate.

[0018] The IMU yaw rate 602 is filtered at 604 to capture the yaw resonance frequency. A phase shift between the steering angle command and the CMG gimbal rate command is achieved in a filter at 612.

[0019] Applying yaw damper control only to steering reduces yaw disturbances, as depicted in graph 700 of FIG. 7. For example, compare yaw rate 402 of FIG. 4 to yaw rate 702 of FIG. 7, and compare filter response 404 of FIG. 4 to filter response 704 of FIG. 7. In an embodiment that does not utilize CMG, steering control alone can be implemented. However, there is a resultant roll disturbance, as depicted in graph 800 of FIG. 8. Rotating the front tires to dampen the yaw disturbance would result in a disturbance in the vehicle roll rate. This disturbance can be compensated by using a control moment gyro to generate a roll torque to counteract the roll disturbance caused by the steering yaw damping. Adding CMG compensation results in a roll rate with the yaw disturbance frequencies removed, as depicted in graph 900 of FIG. 9. This embodiment not only damps the yaw disturbance, but also improves driver comfort, something that a mechanical damper alone cannot do.

[0020] Thus, as discussed above, embodiments of the present invention contemplate adding a secondary control path to a two-wheel self-balancing vehicle with CMG or reaction wheel actuators for steering augmentation and roll balance. These actuators are used to damp yaw disturbances while preventing roll disturbances.

[0021] According to one embodiment, the secondary control path uses a notch filter and gain to isolate the vehicle's natural yaw frequency or any other undesirable vibration with the appropriate phase lag and gain to vary one or more steered wheels of the vehicle to dampen the yaw disturbance. According to this embodiment, the secondary control path uses the augmented steering command to generate a CMG gimbal rate or reaction wheel velocity rate command with the appropriate gain and phase to counteract the roll torque generated by the yaw damping steering command.

[0022] In one embodiment, the secondary control path is mechanized by adding a software path to the existing control mechanization for the baseline vehicle self-balancing control. In one embodiment, the secondary control path can include separate digital or analog controls that apply control signals to the steering actuator and the roll torque actuator, which can be one or more CMGs or one or more reaction wheel roll torque actuators.

[0023] In the above embodiments, the secondary control path may have active tuning to achieve yaw damping while compensating for natural frequency variations due to vehicle dynamics, rather than fixed tuning achieved at the factory or repair shop.

[0024] Referring to block diagram 1000 of FIG. 10, in an embodiment without a CMG, the secondary control path utilizes only steering to maintain balance and has active tuning to achieve yaw damping while compensating for natural frequency variations due to vehicle dynamics, rather than employing fixed tuning achieved at the factory or garage.

[0025] Thus, embodiments of the present invention add a secondary control path to a two-wheel self-balancing vehicle with CMG or reaction wheel actuators for steering augmentation and roll balance. These actuators are used to damp yaw disturbances while preventing roll disturbances.

[0026] These embodiments use a notch filter and gain to isolate the vehicle's natural yaw frequency or other undesirable vibrations with the appropriate phase delay and gain, and vary one or more steered wheels of the vehicle to dampen the yaw disturbance.

[0027] Embodiments may use the augmented steering commands to generate CMG gimbal rate or reaction wheel velocity rate commands with appropriate gain and phase to counteract the roll torque generated by the yaw damping steering commands.

[0028] The embodiment can be mechanized by adding software paths to the existing control mechanization for the baseline vehicle self-balancing control.

[0029] An embodiment may use separate digital or analog controls to apply control signals to the steering actuator and the roll torque actuator, which may be one or more CMGs or one or more reaction wheel roll torque actuators.

[0030] Embodiments can use active tuning to achieve yaw damping while compensating for natural frequency variations due to vehicle varying characteristics, rather than fixed tuning achieved at the factory or repair shop.

[0031] Embodiments can use steering only (no CMG) to maintain balance and use active tuning to achieve yaw damping while compensating for natural frequency variations due to vehicle dynamics rather than fixed tuning achieved at the factory or repair shop.

[0032] Thus, described is a method of controlling a two-wheel self-balancing vehicle ("vehicle") comprising the steps of receiving a yaw rate signal of the vehicle by one or more sensors mounted on the vehicle, obtaining a yaw rate disturbance signal from the yaw rate signal by a signal filter coupled to the one or more sensors, receiving the yaw rate disturbance signal as a control input to an augmentation steering actuator that augments a driver-controlled steering actuator, where the yaw rate disturbance signal is used to generate a torque about a roll axis of the vehicle ("roll torque") that reduces or cancels a roll rate disturbance of the vehicle, and generating, by the augmentation steering actuator, a roll torque in response to the received yaw rate disturbance signal to reduce or cancel said roll rate disturbance of the vehicle.

[0033] According to an embodiment, the augmenting steering actuator modifies the steering angle and thus the vehicle's yaw rate and centrifugal forces, which act on the vehicle's center of gravity and cause changes in the vehicle's roll torque.

[0034] According to a further embodiment, the yaw rate disturbance signal is received as a control input to a control moment gyroscope (GMG) coupled to the vehicle for balancing the vehicle, the yaw rate disturbance signal being used to generate a roll torque in the vehicle that reduces or cancels the yaw rate disturbance in the vehicle, and the CMG generates a roll torque in response to the received yaw rate disturbance signal to reduce or cancel the yaw rate disturbance in the vehicle. [Explanation of symbols]

[0035] 602 IMU Yaw Rate 604 Notch Filter 606 Gain as a function of speed 610 Output to steering 612 Phase Shift 614 Gain as a function of speed

Claims

1. A method for controlling a two-wheeled self-balancing vehicle (the "vehicle"), comprising: receiving a yaw rate signal of the vehicle by one or more sensors attached to the vehicle; obtaining a yaw rate disturbance signal from the yaw rate signal by a signal filter coupled to the one or more sensors; receiving the yaw rate disturbance signal as a control input to an enhanced steering actuator that enhances a driver-controlled steering actuator, and using the yaw rate disturbance signal to generate a torque (the "roll torque") about the roll axis of the vehicle that reduces or cancels out roll rate disturbances of the vehicle; generating, by the enhanced steering actuator, a roll torque in response to the received yaw rate disturbance signal to reduce or cancel out the roll rate disturbances of the vehicle; A method comprising the above steps.

2. The method according to claim 1, wherein the enhanced steering actuator corrects the steering angle and thus the yaw rate and centrifugal force of the vehicle, the centrifugal force of the vehicle acts on the center of gravity of the vehicle, and a change in the roll torque of the vehicle is caused.

3. The method according to claim 1, wherein the step of receiving the yaw rate signal of the vehicle by the one or more sensors attached to the vehicle comprises receiving the yaw rate signal of the vehicle by the one or more sensors selected from a group of sensors consisting of an inertial measurement unit (IMU), a differential accelerometer, a feedback sensor of the steering angle of the vehicle, or a force measurement sensor on the enhanced steering actuator of the vehicle.

4. The method according to claim 1, wherein the yaw rate signal includes a natural frequency of yaw resonance of the vehicle.

5. The method according to claim 1, wherein the step of obtaining the yaw rate disturbance signal from the yaw rate signal by the signal filter coupled to the one or more sensors comprises obtaining the yaw rate disturbance signal from the yaw rate signal by a self-adjusting filter coupled to the one or more sensors that allows for variations in vehicle dynamics.

6. The method according to claim 1, wherein the yaw rate disturbance signal is caused by a yaw impulse induced by the road on which the vehicle is traveling.

7. Receiving the yaw rate disturbance signal as a control input to a control moment gyroscope (CMG) coupled to the vehicle to balance the vehicle, and using the yaw rate disturbance signal to generate a roll torque of the vehicle that reduces or cancels out the yaw rate disturbance of the vehicle; Generating, by the CMG, the roll torque in response to the received yaw rate disturbance signal to reduce or cancel out the yaw rate disturbance of the vehicle; The method according to claim 1, further comprising.

8. A two-wheeled self-balancing vehicle ("vehicle"), An enhanced steering actuator of the vehicle that generates a roll torque for the vehicle; One or more sensors attached to the vehicle for receiving a yaw rate signal of the vehicle; A signal filter coupled to the one or more sensors, obtaining a yaw rate disturbance signal from the yaw rate signal, and providing the yaw rate disturbance signal as a control input to the enhanced steering actuator; Comprising The enhanced steering actuator generates a roll torque that reduces or cancels out a roll rate disturbance of the vehicle in response to the yaw rate disturbance signal; A two-wheeled self-balancing vehicle characterized by this.

9. The vehicle according to claim 8, wherein the enhanced steering actuator corrects a steering angle and thus the yaw rate and centrifugal force of the vehicle, the centrifugal force of the vehicle acts on the center of gravity of the vehicle, and a change in the roll torque of the vehicle is caused.

10. The vehicle according to claim 8, wherein the one or more sensors are selected from a group of sensors including an inertial measurement unit (IMU), a differential accelerometer, a feedback sensor of a steering angle of the vehicle, or a force measurement sensor on the enhanced steering actuator of the vehicle.

11. The vehicle according to claim 8, wherein the yaw rate signal includes a natural frequency of yaw resonance of the vehicle.

12. The vehicle according to claim 8, wherein the signal filter coupled to the one or more sensors and obtaining the yaw rate disturbance signal from the yaw rate signal includes a self-adjusting filter coupled to the one or more sensors and allowing fluctuations in vehicle dynamics to obtain the yaw rate disturbance signal from the yaw rate signal.

13. The vehicle according to claim 8, wherein the yaw rate disturbance signal is caused by a yaw impulse induced by a road on which the vehicle is traveling.

14. The vehicle according to claim 8, further comprising a control moment gyroscope (CMG) coupled to the vehicle to generate a roll torque to balance the vehicle, wherein the signal filter provides the yaw rate disturbance signal as a control input to the CMG that generates a roll torque that reduces or cancels the yaw rate disturbance of the vehicle in response to the yaw rate disturbance signal.

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