METHOD OF CONTROLLING STEERING OF A GROUND VEHICLE
A method of controlling steering of a vehicle through setting wheel angles of a plurality of modular electronic corner assemblies (eModules) is provided. The method includes receiving a driving mode selected from a mode selection menu. A position of a steering input device is determined in a master controller. A velocity of the vehicle is determined, in the master controller, when the determined position of the steering input device is near center. A drive mode request corresponding to the selected driving mode to the plurality of steering controllers is transmitted to the master controller. A required steering angle of each of the plurality of eModules is determined, in the master controller, as a function of the determined position of the steering input device, the determined velocity of the vehicle, and the selected first driving mode. The eModules are set to the respective determined steering angles.
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This application is a divisional application of, and claims the benefit of priority from, U.S. application Ser. No. 14/075,262, which was filed on Nov. 8, 2013, which is incorporated by reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTThis invention was made with government support under NASA Space Act Agreement number SAA-EA-10-017. The invention described herein may be manufactured and used by or for the U.S. Government for U.S. Government (i.e., non-commercial) purposes without the payment of royalties thereon or therefor.
TECHNICAL FIELDThe present disclosure is related to a method of controlling steering of a vehicle.
BACKGROUNDAn ideal vehicle design for a driver who is commuting within a congested area might be a relatively small, fuel efficient vehicle that is easy to maneuver and park. However, on other occasions, the same driver may wish to transport multiple passengers and/or cargo, or may wish to operate in different drive modes. For such a driver, a conventional vehicle chassis and powertrain, having a fixed configuration and mechanically coupled steering, braking, and propulsion systems, may be less than optimal.
SUMMARYA modular robotic vehicle is disclosed herein. The vehicle is electrically driven, via by-wire commands, using energy from a high-voltage battery pack and an associated power electronics module. The vehicle is controlled by way of a distributed control network having a primary and secondary master controller and multiple embedded control modules, with each control module having a corresponding steering, propulsion, and braking control task for a given corner of the vehicle. Multiple levels of control redundancy are provided, e.g., with multiple control modules used to ensure a “fail safe” backup for operationally critical functions.
Additionally, each corner of the vehicle includes a modular, self-contained “eModule”, housing electric steering, propulsion, braking, and suspension subsystems. Independent control of each eModule is supervised by the primary and secondary master controllers, with the various control modules embedded within the eModules communicating as needed with the master controller via Ethernet for Control Automation Technology (EtherCAT), control area network (CAN) bus, or another suitable high-speed connection.
Driver input commands are received by the master controller from various devices, such as a steering wheel and/or joystick, a brake pedal, an accelerator pedal, and a human machine interface (HMI) screen or touchpad. These electrical input signals are transmitted to the primary and secondary master controllers. The primary and secondary master controllers then determine the driver's desired control response, and issue individual commands to each of the control modules embedded within the eModules that are affected by the driver inputs. The entire control operation is by-wire as noted above, i.e., lacking a direct mechanical linkage between the driver input devices and the steering, propulsion, or braking subsystems being controlled in response to the driver's inputs.
One possible aspect of the disclosure provides a method of controlling steering of a vehicle through setting wheel angles of a plurality of modular electronic corner assemblies (eModules) relative to a chassis. The method includes receiving a driving mode selected from a mode selection menu. A position of a steering input device is determined in a master controller. A velocity of the vehicle is determined, in the master controller, when the determined position of the steering input device is near center. A drive mode request corresponding to the selected driving mode is transmitted to a plurality of steering controllers. A required steering angle of each of the plurality of eModules is determined, in the master controller, as a function of the determined position of the steering input device, the determined velocity of the vehicle, and the selected first driving mode. The eModules are set to the respective determined steering angles.
In another aspect of the disclosure, a method of controlling steering of a vehicle through setting wheel angles of a plurality of eModules, relative to a chassis is provided. The method includes activating a mode selection menu. A driving mode selected from the mode selection menu is received. A master controller determines the position of a steering input device and a velocity of the vehicle. The wheel angle for each of the eModules is determined as a function of the selected driving mode, the position of the steering input device, and the determined velocity of the vehicle. The determined wheel angles are transmitted for each of the plurality of eModules to a respective steering controller.
In yet another aspect of the disclosure, a method of controlling steering of a vehicle through setting wheel angles of a plurality of eModules relative to a chassis is provided. The method includes activating a mode selection menu and receiving a selected first driving mode selected from the mode selection menu. A master controller determines when a brake pedal is activated. A first drive mode request corresponding to the selected first driving mode is transmitted to a plurality of steering controllers when the brake pedal is determined to be activated. Each of the steering controllers corresponds to a respective eModule.
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the several Figures, an example modular robotic vehicle 10 is shown schematically in
A particular modular component providing a foundation to the design set forth herein is a self-contained electric corner assembly or “eModule” 40, with one eModule 40 being positioned at each corner of the vehicle 10, i.e., a left front (LF) 25, a right front (RF) 27, a left rear (LR) 29, and a right rear (RR) 30 of the vehicle 10. Each eModule 40 includes a drive wheel 18. A typical four-wheel design as shown in
Referring to
The steering module 46 is configured for directing steering of the respective eModule 40, as will be explained in more detail below. The steering module 46 includes a first and a second steering controller 50S1, 50S2 and a first and second steering sensor 58A, 58B, i.e., encoder read head. Functional redundancy within the steering module 46 is enabled via the use of the first and second steering controllers 50S1, 50S2, as shown in
Referring to
Referring to
The communications module is configured for communicating between each of the primary and secondary master controllers 50, 150 and the corresponding steering, propulsion, and braking modules 46, 48, 49.
Referring again to
Further with respect to
Referring to
Referring to
Referring to
The first and second steering controllers 5051, 50S2, positioned with respect to the upper portion 70, locally control the steering function of the respective eModule 40. As described above, the two steering controllers 5051, 5052 may be used for functional redundancy over all steering functions. While omitted for simplicity, the upper portion 70 may include a removable access cover which provides direct access to the steering controllers 5051, 5052. A suspension assembly having a spring and damper assembly 37 are housed within or connected to the lower portion 74, e.g., electronics, wiring, conduit, and encoders (not shown) as needed for measuring and communicating information pertaining to the orientation of the drive wheel 18 with respect to a pivot axis 19 (see
Referring to
Still referring to
The seal 157 shown in
Referring again to
With reference to
With continued reference to
Use of the modular, independently-controlled eModules 40 of
Referring to
Park mode 118 means that angles of the LF, RF, LR, and RR wheels 18 relative to a front F of the vehicle 10 such the RF and LR wheels 18 are at the same angle and the LF and RR wheels 18 are at the same angle. Thus, in park mode 118 the LF and RF wheels 18 and the LR and RR wheels 18 would point outward with respect to the X axis of the vehicle 10, thereby causing wheel scrub and preventing vehicular motion in any direction without the use of wheel brakes.
As noted above, the primary and secondary master controllers 50, 150 are programmed to execute a wide spectrum of different steering modes, including the two-wheel, four-wheel, diamond, and omni-directional or “crab” steering noted above. The modular design of the eModules 40, along with the distributed control network with the primary and secondary master controllers 50, 150 at its center, enables such flexibility. A driver, using the HMI screen 38 of
It should be appreciated that only the 2WS 110, 4WS 112, or omni-directional steering 116 modes may also be changed while the vehicle 10 is stationary or when the vehicle 10 is in motion. More specifically, a joystick 132 position is selected by the driver for a particular steering mode and then a button 133 on the joystick 132 is pressed to activate the selected mode. However, changing steer modes requires several conditions to be valid. First, the wheel angles must be near zero degrees, e.g., driving forward. Second, the vehicle velocity must be below a maximum velocity of the selected steering mode. By way of a non-limiting example, the 2WS mode 110 may have a maximum velocity of 40 mph and the omni-directional steering 116 mode may be 15 mph. Therefore, in order to switch from the 2WS mode 110 to the Omni-directional steering 116 mode, the vehicle 10 must be less than or equal to 15 mph. Third, the joystick 132 Z-axis (Yaw) must be near zero. Since the omni-directional steering mode 116 uses the Z-axis to turn, the angle must be near zero so as to prevent sudden turns when the vehicle 10 transitions into the omni-directional steering 116 mode.
The ability of the vehicle 10 to change steering modes while the vehicle 10 is in motion allows for quick changes without distracting the driver from the field of view, e.g., the roadway. Conversely, the system may be configured such that the HDMI menu 38 may only be activated when the vehicle 10 is stopped. Although a menu system may be used when the vehicle 10 is in motion, it may be configured to only show valid modes for selection when the vehicle 10 is in motion.
Referring to
Referring again to
At step 250, the master controllers 50, 150 receive a selected first driving mode, selected from the mode selection menu. The master controllers 50, 150 then determine at step 260 when the brake pedal 34 is activated. A first drive mode request, corresponding to the selected first driving mode, is transmitted at step 270 to a plurality of steering controllers 50S1, 50S2 when the brake pedal 34 is determined to be activated. Each of the steering controllers 50S1, 50S2 corresponds to a respective eModule 40.
Once the first drive mode request is transmitted, the method proceeds to initiating a steering algorithm 400, 500, 600, 700, corresponding to the selected first drive mode request at 280. The required steering algorithm 400, 500, 600, 700 may correspond to the 2WS mode 110, 4WS mode 112, diamond steering mode 114, omni-directional steer mode 116, and park mode 118, which are all executed by the master controller at step 280. Generally, the steering algorithm 400, 500, 600, 700 determines the required steering angle of each of the plurality of eModules 40 as a function of a determined position of the steering input device 32, the determined velocity of the vehicle 10, and the selected first driving mode.
When the vehicle 10 is already operating in a driving mode and in motion, the master controllers 50, 150 may receive a request for a second driving mode, also selected from the mode selection menu, at step 300. This second driving mode is different from the first driving mode and, as described in more detail below, may only be entered from the first driving mode when certain requirements are met.
The position of the steering input device 32 is determined at step 310. The position of the steering input device 32 may be an angle of the steering wheel, relative to a front F center of the vehicle 10. A determination is made, in the master controllers 50, 150 at step 320, as to whether the position of the steering input device 32 is near center. If the position of the steering input device 32 is not near center, then the selection is aborted and the method proceeds to step 240. The position of the steering input device 32 is only used if the vehicle 10 is in motion. If the vehicle 10 is stopped, the steering input device 32 may be in any position when selecting the driving mode.
If the position of the steering input device 32 is near center, then the method proceeds to step 330. At step 330, a determination of the vehicle speed is made, in the master controller. If the vehicle speed is greater than a maximum velocity, then the selection is aborted and the method proceeds to step 240. If the vehicle speed is determined to be no greater than the maximum velocity, then the method proceeds to step 350, where a second drive mode request is sent to the steering controller 50S1, 50S2.
The master controllers 50, 150 then determine at step 310, the position of the steering input device 32. The master controllers then determine a velocity of the vehicle 10 when the determined position of the steering input device 32 is near center.
A second drive mode request corresponding to the selected second driving mode is transmitted at step 320 to the plurality of steering controllers 50S1, 50S2 when the velocity of the vehicle 10 is determined to be no greater than a maximum velocity.
A steering algorithm is executed by the master controllers 50, 150 at step 280. Generally, the steering algorithm determines the required steering angle of each of the plurality of eModules 40 as a function of the determined position of the steering input device 32, the determined velocity of the vehicle 10, and the selected first driving mode. It should be appreciated that the determined steering angles may be updated at any desired frequency. By way of a non-limiting example, the determined steering angles may be updated at 100 Hertz (Hz). After the required steering angles are determined, each of the eModules is set to the respective determined steering angles at step 280.
Referring to
Next, an instantaneous center of rotation (ICR) is set to be along a centerline of the LR and RR wheels, i.e., along a Y axis of the vehicle 10 at step 425. Then, the angle setting of the LR and RR wheels is set to 0 degrees at step 430. A coordinate position of the ICR in an XY coordinate plane is then calculated as a function of the calculated steering angle at step 435. The steering angles of each of the LF and RF wheels are next calculated to intersect with the calculated ICR at step 440.
If the LF and RF wheels have a steering axis and a wheel axis that are offset, i.e., caster wheel offset, then the caster wheel offsets for each of the LF and RF wheels is calculated at step 445. Then, the wheel angle offsets are calculated to align the LF and RF wheel centers with the calculated ICR at step 450, as illustrated in
Next, the wheel angles of the LF and RF wheels are calculated, relative to the front F of the vehicle 10 at step 455. Then, the calculated wheel angles are written to the main memory of the master controllers 50, 150 at 460.
Referring to
When the determined position of the steering input device 32 is not near 0 degrees, an ICR lateral line offset is calculated as a function of the velocity of the vehicle 10 at step 520. When the velocity of the vehicle 10 is no less than a minimum velocity, the ICR lateral line is calculated to intersect a center of the vehicle 10. When the velocity of the vehicle 10 is greater than a maximum velocity, the ICR lateral line is set to intersect the center of the LR and RR wheels. When the velocity of the vehicle 10 is greater than the minimum velocity and no greater than the maximum velocity, then the ICR lateral line is set to transition linearly from the position corresponding to velocity that is no less than the minimum velocity and the velocity that is greater than the maximum velocity. By way of a non-limiting example, the minimum velocity may be 5 miles per hour (mph) and the maximum velocity may be 10 mph.
At step 525, the steering angle is calculated as a function of the steering input device 32 angle and a max steer angle. The max steer angle is dependent on the steering case of the vehicle 10, i.e., 2WS 110, 4WS 112. When 2WS 110 is selected, the max steer angle is at a first angle and when 4WS is selected, the max steer angle is at a second angle, different from the first angle. Therefore, during transition, the max steer angle varies linearly with velocity of the vehicle 10 between the value of the first angle and the value of the second angle.
Next, at step 530, a coordinate position of the ICR in an XY coordinate plane is then calculated as a function of the calculated steering angle. The steering angles of each of the LF and RF wheels are next calculated to intersect with the calculated ICR at step 540. In turn, the wheel angle of each of the LR, RR, LF, and RF wheel is calculated to intersect with the calculated ICR at step 535, as illustrated in
If the LR, RR, LF, and RF wheels have a steering axis and a wheel axis that are offset, i.e., caster wheel offset, then the caster wheel offsets for each of the LR, RR, LF, and RF wheels are calculated at step 540. Then, the wheel angle offsets are calculated to align the LR, RR, LF, and RF wheel centers with the calculated ICR at step 545.
Next, the wheel angles of the LR, RR, LF, and RF wheels are calculated, relative to the front F of the vehicle 10 at step 550. Then, the calculated wheel angles are written to the main memory of the master controllers 50, 150 at step 555.
As described previously, other modes, such as the diamond steer mode 114 illustrated in
Further, vehicle motion in the diamond steer mode 114 from another mode may only be achieved if a minimum threshold of the steering angle of the steering input device 32 is exceeded and a defined amount of displacement of the accelerator pedal 36, i.e., throttle, is not exceeded. By way of a non-limiting example, of the steering input device 32 is turned to the minimum threshold of 45 degrees, in either direction, and the defined amount of displacement of the accelerator pedal 36 is exceeded.
In another non-limiting example, the diamond steer mode 114 may be achieved when the defined amount of displacement of the accelerator pedal 34 is achieved and the steering input device 32 is turned slowly in the desired direction of displacement. As such, if the steering input device 32 is at center, i.e., 0 degrees, the vehicle will stop. However, if the steering input device 32 is at the minimum threshold of 45 degrees, the vehicle will turn in the direction of the steering input device 32, i.e., left or right.
In yet another non-limiting example, the diamond steer mode 114 may be achieved by using a combination of varying the angle of the steering input device 32 and the amount of displacement of the accelerator pedal 34.
Referring to
Alternatively, referring to
Another parallel parking maneuver of the vehicle 10 is illustrated in
With reference to
Referring to
At step 610, a normalized joystick 132 yaw angle is determined. The angle may be within a range of 0+/−1 degrees. At step 615, if the joystick 132 yaw angle is not determined to be less than a minimum yaw angle or greater than a maximum yaw angle, then the wheel angles of the vehicle 10 are written to the main memory in the master controllers 50, 150 at step 620. However, if the joystick 132 yaw angle is determined to be less than a minimum yaw angle or greater than a maximum yaw angle, the algorithm 600 proceeds to step 625. At step 625, the steer angle is calculated as a function of the max steer angle and the joystick 132 yaw angle about the Z-axis. The max steer angle limits the turning radius of the vehicle 10 such that the combined maximum direction vector angle and maximum steering angle of any wheel does not exceed the limits of the steering motor, e.g., +/−160 degrees.
Next, the steering radius of the vehicle 10 is calculated from the center C of the vehicle 10 at step 630. The coordinate position of the ICR is calculated as a function of the calculated steering radius and the directional vector at step 635. Then, the angles of the LF eModule, the RF eModule, the LR eModule, and the RR eModule are calculated at step 640, relative to the location of the steering motor.
If the LR, RR, LF, and RF wheels have a steering axis and a wheel axis that are offset, i.e., caster wheel offset, then the caster wheel offsets for each of the LR, RR, LF, and RF wheels are calculated at step 645. Then, the wheel angle offsets are calculated to align the LR, RR, LF, and RF wheel centers with the calculated ICR at step 650.
Next, the wheel angles of the LR, RR, LF, and RF wheels are calculated, relative to the front F of the vehicle 10 at step 655. At step 620, the wheel angle of the LF eModule, the RF eModule, the LR eModule, and the RR eModule are recorded to the memory in the master controllers 50, 150.
Referring to
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.
Claims
1. A method of controlling steering of a vehicle through setting wheel angles of a plurality of modular electronic corner assemblies (eModules), the method comprising:
- activating a driver interface device;
- receiving a selected first driving mode selected from the driver interface device;
- determining, by a master controller, when a brake pedal is activated; and
- transmitting a first drive mode request corresponding to the selected first driving mode to a plurality of steering controllers when the brake pedal is determined to be activated;
- wherein each of the plurality of steering controllers corresponds to a respective one of the plurality of eModules.
2. A method, as set forth in claim 1, further comprising:
- determining a position of a steering input device;
- determining, in the master controller, a required steering angle of each of the plurality of eModules as a function of the determined position of the steering input device and the selected first driving mode; and
- setting the eModules to the respective determined steering angles.
3. A method, as set forth in claim 2, further comprising:
- receiving a second driving mode selected from the driver interface device;
- determining, in the master controller, the position of the steering input device;
- determining, in the master controller, a velocity of the vehicle when the determined position of the steering input device is near center;
- transmitting a second drive mode request corresponding to the selected second driving mode to the plurality of steering controllers when the velocity of the vehicle is determined to be no greater than a maximum velocity; and
- determining, in the master controller, a required steering angle of each of the plurality of eModules as a function of the determined position of the steering input device and the selected first driving mode; and
- setting the eModules to the respective determined steering angles.
4. A method, as set forth in claim 3, further comprising:
- receiving a command to activate a mode selection menu;
- determining, by the master controller, if the vehicle is in motion; and
- activating the driver mode selection menu when the vehicle is determined to not be in motion.
5. A method, as set forth in claim 1, further comprising:
- determining, with at least one location device, a spot defined between objects adjacent the vehicle;
- wherein determining the wheel angle is further defined as determining the wheel angle for each of the plurality of eModules as a function of the driving mode, the position of the steering input device, the determined velocity of the vehicle, and the spot defined between objects adjacent the vehicle.
Type: Application
Filed: Jan 18, 2016
Publication Date: May 12, 2016
Applicants: GM GLOBAL TECHNOLOGY OPERATIONS LLC (Detroit, MI), The U.S.A. As Represented by the Administrator of the National Aeronautics and Space Administration (Washington, DC)
Inventors: Andrew D. Dawson (League City, TX), William J. Bluethmann (Houston, TX), Chunhao J. Lee (Troy, MI), Robert L. Vitale (Macomb Township, MI), Raymond Guo (Seabrook, TX), Venkata Prasad Atluri (Farmington Hills, MI)
Application Number: 14/997,850