Patent Description:
Reversing a vehicle with a connected trailer is a nontrivial and counter intuitive process which often frustrates consumers and poses challenges while attempting to maneuver trailers into tight spots. Drivers are often confused as to which way to turn the vehicle's steering wheel to get the desired change in direction of the trailer. The recent addition of Trailer Reverse Assist (TRA) type functions remedies this situation by allowing the driver/operator to steer the trailer directly with the vehicle while backing. However, with reference to <FIG>, the control system in a vehicle <NUM> enabling Trailer Reverse Assist functions are prone to small errors during straight line backing of a trailer <NUM>, which may result in large drift of the trailer <NUM> from the implied/expected/desired backing direction. With reference to <FIG>, this drift must be periodically and manually adjusted by the driver and is a noticeable inconvenience as it interrupts the smooth and intuitive operation of the system. Note that in <FIG>, the Y-scale is exaggerated for description clarity.

Thus, there is a need to provide a system and method that removes such drift and is also able to provide real-time updates to the calibration of TRA type systems to further mitigate drift.

From the publication <CIT>, which shows that features of the preamble of claim <NUM>, a trailer backup assist system for a vehicle reversing a trailer is known. A steering input device controls a desired curvature. A controller is in communication with the steering input device and is configured to generate steering commands for the vehicle to guide the vehicle and trailer onto a straight path when a straight backup request is initiated via the steering input device.

The trailer backup assist system steers the vehicle as necessary for causing the trailer to be backed along a curved backing path as desired path. If the vehicle starts reversing the trailer along this curved backing path and continue backing up along a desired path in the heading direction of the trailer, the deviation of the trailer is detected based on a hitch angle unequal to zero. Then, the deviation is corrected to merge with the desired path.

It is an object of a known parking system (<CIT>) to promptly correct a deviation from a target parking route by detecting the present location and performing a corrected steering according to the deviation. When a main control system starts performing an automatic parking to a parking spot, the vehicle starts along a parking target route. If the vehicle deviates from the target parking route, a corrected auxiliary parking route is calculated. Thus, the actual traveling route gradually approaches the original target parking route. Only the vehicle is automatically parked. A trailer coupled to the vehicle is not mentioned.

The document <CIT> discloses a guidance system for a vehicle reversing a trailer. The system includes a display and a controller configured to generate a steering icon on the display. The steering icon recommends a steering direction and a steering magnitude related to a steering device of the vehicle in order to correct a deviation from an intended backing path for assisting a driver of a vehicle in reversing a trailer along an intended backing path. A hitch angle between vehicle and trailer is measured, determining whether the vehicle and trailer have deviated from the intended backing path based on the measured hitch angle.

An object of the invention is to fulfill the need referred to above. In accordance with the principles of a present embodiment, this objective is achieved by providing a trailer reverse assist system for vehicle straight line backing-up of a trailer connected to the vehicle via a coupler. The vehicle has a steering system and vehicle dynamic sensors for detecting vehicle operating parameters. The system includes a coupler angle detection sensor constructed and arranged to detect a zero-degree angle of the trailer relative to the vehicle. A trailer reverse assist module is constructed and arranged to receive signals from the vehicle dynamic sensors and the coupler angle detection sensor. The trailer reverse assist module is associated with the steering system for causing changes to the vehicle's steering while backing up the trailer on an intended straight line implied path. A drift controller is constructed and arranged to receive signals from the vehicle dynamic sensors. The drift controller is electrically connected with the trailer reverse assist module. When the vehicle is backing up the trailer on the intended straight line implied path and since the coupler angle sensor, detecting the zero degree angle, may not be perfectly calibrated, based on the signals from the vehicle dynamic sensors, the drift controller is constructed and arranged <NUM>) to estimate a distance that the trailer has drifted from the straight line desired path and <NUM>) in a closed-loop feedback manner, to provide a drift correction signal to the trailer reverse assist module for modifying a value of the zero degree angle and thus cause adjustment of the steering system to realign the trailer towards the straight line implied path without manual steering intervention.

In accordance with another aspect of an embodiment, a method is provided for backing up a trailer along a straight line implied path using a vehicle. The vehicle has a steering system, a trailer reverse assist module associated with the steering system for causing changes to the vehicle's steering while backing up the trailer, and vehicle dynamic sensors for detecting vehicle operating parameters. The method includes detecting a zero-degree angle of the trailer relative to the vehicle. The trailer reverse assist module determines if the detected zero-degree angle is substantially <NUM> degrees. The trailer reverse assist module receives signals from the vehicle dynamic sensors. The method provides a drift controller electrically connected with the trailer reverse assist module. The signals from the vehicle dynamics sensors are also received by the drift controller. When the vehicle is backing up the trailer intending to move the trailer along the straight line implied path and when the trailer reverse assist module determines that the relative trailer angle is substantially <NUM> degrees and since the zero degree angle is not detected perfectly, based on the signals from the vehicle dynamic sensors received by the drift controller, the drift controller estimates a distance that the trailer has drifted from the straight line implied path. In a closed loop feedback manner, the drift controller provides a drift correction signal to the trailer reverse assist module to modify the value of the zero degree angle and thus cause adjustment of the steering system so as to realign the trailer towards the straight line implied path without manual steering intervention.

Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.

The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:.

With reference to <FIG>, a Trailer Reverse Assist (TRA) system is shown, generally indicated at <NUM> for assisting a vehicle <NUM>' in backing up of a trailer <NUM> coupled thereto via coupler or hitch <NUM>. The vehicle <NUM>' includes a Trailer Reverse Assist (TRA) module <NUM>, preferably of the type disclosed in <CIT>. As best shown in <FIG>, the TRA module <NUM> is an electronic control unit (ECU) including or connected with a separate vehicle steering module <NUM>. In the embodiment, the steering wheel module <NUM> is shown to be part of the TRA module <NUM>. A coupler angle detection sensor <NUM> and an input device <NUM> are connected to the TRA module <NUM>. The sensor <NUM> and input device <NUM> may already be existing components and incorporated into the vehicle <NUM>'. For example, the input device <NUM> may be a joystick controller that is used with a navigation/information system. The sensor <NUM> may be used to measure the coupler or hitch angle which represents relative angle between the vehicle and the trailer. The sensor <NUM> may be one or multiple sensors measuring relative distance between the vehicle <NUM>' and the trailer <NUM> and using the varied distance to calculate hitch angle. The sensor(s) <NUM> may use horizontal or vertical features on the trailer <NUM> in the distance measurement. In the embodiment, the sensor <NUM> is a camera, preferably a camera which is already installed in the vehicle <NUM>', such as a back-up camera. The camera <NUM> may capture an image and image analysis may be used to calculate the hitch angle. A distinct marking <NUM> can be established on the trailer <NUM> and captured by the camera <NUM> for analysis.

The steering module <NUM> includes a processor circuit <NUM> that is constructed and arranged to actively change a steering angle of the front axle wheels <NUM> (<FIG>) without the vehicle driver giving a respective input through the vehicle steering wheel <NUM>. The steering wheel angle is detected by a sensor <NUM> and the steering angle is changed via an actuator <NUM> coupled with the steering system <NUM> such as with a shaft <NUM> connected with the steering wheel <NUM> so as to provide torque to the steering wheel. The shaft <NUM> can be considered to be part of the steering wheel <NUM>. The steering module <NUM> may also include the capability of additionally steering the rear axle wheels. With reference <FIG>, based on signals <NUM> obtained from conventional vehicle dynamic sensors <NUM> (e.g., wheel rotations, and/or distance traveled and steering wheel angle obtained from sensor <NUM>), a user requested steering signal <NUM> from the input device <NUM> and an observed trailer orientation signal <NUM> obtained from the sensor <NUM>, the processor circuit <NUM> computes corrective actions to be taken and initiates, via steering output signal <NUM>, the steering actuator <NUM> in order to maneuver the vehicle <NUM>' and trailer <NUM> accordingly. It is noted that steering wheel angle sensor <NUM> can be considered to be part of the vehicle dynamic sensors.

In the case when a user provides an input to the TRA module <NUM> for straight line backing with an aligned trailer <NUM> (trailer angle being approximately <NUM> degrees relative to the vehicle axis A), the vehicle <NUM>' is expected to back straight up as if there was no trailer attached thereto and with the driver holding the steering wheel <NUM> straight. The TRA module <NUM> works well for its intended purpose, but, in practice, this <NUM> degree angle is not maintained since the trailer <NUM> tends to swing to one side due to small imperfections in the system alignment. The conventional TRA module <NUM> for straight line backing involves the vehicle steering in an attempt to keep the trailer angle sensor <NUM> reading zero degrees. When the value reported for <NUM> degree trailer angle is not perfectly calibrated (due to imprecise detection by the sensor <NUM>), this is equivalent to connecting the trailer <NUM> to the vehicle <NUM>' with a small angle error and then backing up. When this happens, the vehicle <NUM>' turns gradually and follows the trailer <NUM>. As noted above with regard to <FIG>, as a result, the reversing direction deviates slightly from the implied straight-line path.

In accordance with the embodiment, a drift controller <NUM> is provided as part of, or preferably connected to, the TRA module <NUM> to mitigate drift of the trailer <NUM> during straight line backing. As noted above, the vehicle <NUM>' has a steering wheel angle sensor <NUM> and the vehicle can also detect the distance traveled by each road wheel individually (via sensors <NUM>). Given this data, an estimate can be determined as to how far away the vehicle or trailer is from the implied straight line path (an imaginary line which connects the starting position and the desired final position). This estimate can be considered to be a path offset estimate. This path offset estimate can be used to instruct the steering wheel module <NUM> to apply torque to the steering wheel via actuator <NUM> to bring the vehicle or trailer back onto the implied path. This can be termed as drift correction.

With reference to <FIG> and <FIG>, in the embodiment, the drift controller <NUM> uses the signals <NUM> obtained from vehicle dynamic sensors <NUM> (e.g., sensing vehicle operating parameters such as wheel rotations, and/or distance traveled, with steering wheel angle obtained from sensor <NUM>) to estimate the path offset or deviation of the trailer <NUM> and propose a new path (heading angle) which closes the accumulated path error without requiring user intervention. Thus, as best shown in <FIG>, the drift controller <NUM> receives the same precision vehicle dynamic input signals <NUM> that are used to drive the TRA module <NUM>. These input signals <NUM> are sufficient to estimate the deviation of the position and orientation of the vehicle <NUM>' from the initial straight line position thereof. This deviation is then used as feedback to control the TRA module <NUM> to cause the vehicle <NUM>' to realign the trailer <NUM> back to its original path.

The drift controller <NUM> can be any type of controller that sends a drift correction signal <NUM> as an input to the TRA module <NUM> for controlling the steering module <NUM> to cause changes to the steering system <NUM>. The drift correction module <NUM> can also be employed to recalibrate or modify the value of the zero relative trailer angle in the TRA module <NUM>. For example, drift correction module <NUM> may employ a proportional control feedback to the TRA module <NUM> such that a steady (equilibrium value) correction to the TRA module is obtained during a maneuver. The angle sensor <NUM> can be recalibrated (by permanently subtracting the correction from the angle sensor). Once this is done, the TRA module <NUM> and thus the steering module <NUM> will be driven exponentially back to a zero offset.

<FIG> shows a simple first order exponential path planner. The controller <NUM> constructs a smooth path which converges to the desired path and can be easily interpreted as steering commands to the TRA module <NUM> and does not involve excessive back and forth motions of the steering wheel <NUM>. Thus, the proportional controller <NUM> relating heading angle correction per unit offset translation has an exact analytic solution and is an exponential path. With reference to <FIG>, the controller <NUM> employs the arc tangent function <NUM> which converts slope to angle. The trailer heading should be - atan (Trailer Offset Error * K) and the trailer angle sensor <NUM> can have its <NUM> degree calibration value adjusted by exactly this amount.

Any closed loop control scheme can be applied to correct the above-mentioned error. One example embodiment of estimating the position of the vehicle <NUM>' is to track, via signals <NUM>, the LEFT and RIGHT rear wheel displacement combined with the steering wheel angle signal from sensor <NUM>, and constant steering ratio, and constant wheel base. Thus, for example, with reference to <FIG>, the steps for performing a method of an embodiment are shown. In step <NUM>, upon start of the routine, the path offset is assumed to be <NUM> and the heading angle θ is also assumed to be <NUM> with the vehicle orientation assumed to be along the straight line implied path. In step <NUM> the TRA <NUM> determines if the user input is <NUM> and if the trailer angle (from sensor <NUM>) is substantially <NUM>. If not, the routine returns to step <NUM>, but if so, in step <NUM>, the drift controller <NUM> (<FIG>) calculates a path offset, for example by: <MAT> Δs = average of rear wheel displacements since last step <MAT> <MAT> <MAT> <MAT>.

The drift correction signal <NUM> from the drift controller <NUM> is fed back to the TRA module <NUM> in step <NUM> so as to recalibrate or modify the value of the zero relative trailer angle in the TRA module <NUM>. Thus, there is a new offset every cycle. As shown in <FIG>, the above calculations are executed in a processor circuit or a path offset estimator <NUM> of controller <NUM> and the result is inputted to the drift correction module <NUM> and then to the TRA module <NUM>.

Thus, the TRA module <NUM> functions as usual when the user provides active input and the new system <NUM> overrides the conventional operation of the TRA module <NUM> and enables a more precise path following feature to back the vehicle in a perfectly straight line. Thus, employment of the drift controller <NUM>:.

There are many different ways to achieve a similar feed-back result. Step <NUM> of <FIG> computes the offset for the center of the rear axle for the vehicle <NUM>'. Another approach is to compute the distance offset for a different point on the vehicle <NUM>', or a point on the trailer <NUM> (e.g., the center of the axle on the trailer). It is noted that speed instead of displacement measurements can be used. The yaw rate can also be used. All four conventional wheel sensors can be employed. Since the Steering Ratio is not typically constant, more exact relationships as well as geometries of the steering system and wheel slip can be employed to improve the estimate.

The operations and algorithms described herein can be implemented as executable code within the processor circuit <NUM> and path offset estimator <NUM> as described, or stored on a standalone computer or machine readable non-transitory tangible storage medium that are completed based on execution of the code by a processor circuit implemented using one or more integrated circuits. Example implementations of the disclosed circuits include hardware logic that is implemented in a logic array such as a programmable logic array (PLA), a field programmable gate array (FPGA), or by mask programming of integrated circuits such as an application-specific integrated circuit (ASIC). Any of these circuits also can be implemented using a software-based executable resource that is executed by a corresponding internal processor circuit such as a micro-processor circuit (not shown) and implemented using one or more integrated circuits, where execution of executable code stored in an internal memory circuit causes the integrated circuit(s) implementing the processor circuit to store application state variables in processor memory, creating an executable application resource (e.g., an application instance) that performs the operations of the circuit as described herein. Hence, use of the term "circuit" in this specification refers to both a hardware-based circuit implemented using one or more integrated circuits and that includes logic for performing the described operations, or a software-based circuit that includes a processor circuit (implemented using one or more integrated circuits), the processor circuit including a reserved portion of processor memory for storage of application state data and application variables that are modified by execution of the executable code by a processor circuit. The memory circuit can be implemented, for example, using a non-volatile memory such as a programmable read only memory (PROM) or an EPROM, and/or a volatile memory such as a DRAM, etc..

Claim 1:
A trailer reverse assist system for vehicle (<NUM>) straight line backing-up of a trailer (<NUM>) connected to the vehicle (<NUM>) via a coupler (<NUM>), the vehicle (<NUM>) having a steering system (<NUM>) and vehicle dynamic sensors (<NUM>) for detecting vehicle operating parameters, the system comprising:
a coupler angle detection sensor (<NUM>) constructed and arranged to detect a zero degree angle of the trailer (<NUM>) relative to the vehicle (<NUM>),
a trailer reverse assist module (<NUM>) constructed and arranged to receive signals from the vehicle dynamic sensors (<NUM>) and the coupler angle detection sensor (<NUM>), the trailer reverse assist module (<NUM>) being associated with the steering system (<NUM>) for causing changes to the vehicle's steering while backing up the trailer (<NUM>) on an intended straight line implied path, and
a drift controller (<NUM>) constructed and arranged to receive signals from the vehicle dynamic sensors (<NUM>), the drift controller (<NUM>) being electrically connected with the trailer reverse assist module (<NUM>),
characterized in that when the vehicle (<NUM>) is backing up the trailer (<NUM>) on the intended straight line implied path and since the coupler angle detection sensor (<NUM>), detecting the zero degree angle, is not perfectly calibrated, based on the signals from the vehicle dynamic sensors (<NUM>), the drift controller (<NUM>) is constructed and arranged <NUM>) to estimate a distance that the trailer (<NUM>) has drifted from the straight line desired path and <NUM>) in a closed-loop feedback manner, to provide a drift correction signal (<NUM>) to the trailer reverse assist module (<NUM>) for modifying the value of the zero degree angle and thus cause adjustment of the steering system (<NUM>) to realign the trailer (<NUM>) towards the straight line implied path without manual steering intervention.