Trailer angle detection target plausibility

According to one aspect of the present invention, a system for determining target plausibility is comprised of an imaging device for imaging a scene and generating image data, sensors for generating hitch angle measurements, steering angle measurements, and vehicle speed measurements. A controller in communication with the imaging device and the sensors, wherein when a driving condition is satisfied, the controller calculates a hitch angle and selects a plausible target from the imaged scene based on the image data and the calculated hitch angle.

FIELD OF THE INVENTION

The disclosure made herein generally relates to driver assist systems in vehicles, and more particularly to a trailer backup system employing image based target direction.

BACKGROUND OF THE INVENTION

Some trailer backup assist systems implement image based target detection to monitor the position of a target to determine a hitch angle between a tow vehicle and a trailer. In some instances, image based target detection can mistakenly image an unreliable or false target, which results in erroneous hitch angle calculations. In view of this shortcoming, a system and method for determining target plausibility is disclosed herein.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a system for determining target plausibility is comprised of an imaging device for imaging a scene and generating image data, sensors for generating hitch angle measurements, steering angle measurements, and vehicle speed measurements. A controller in communication with the imaging device and the sensors, wherein when a driving condition is satisfied, the controller calculates a hitch angle and selects a plausible target from the imaged scene based on the image data and the calculated hitch angle.

According to another aspect of the present invention, a method for determining target plausibility is comprised of an imaging scene and generating image data, generating hitch angle measurements, steering angle measurements, and vehicle speed measurements, calculating a hitch angle when a driving condition is satisfied, and selecting a plausible target from the imaged scene based on the image data and the calculated hitch angle.

According to yet another aspect of the present invention, a method for determining target plausibility is comprised of the steps of imaging a scene and generating image data, detecting at least one target in the imaged scene, calculating a hitch angle when a hitch angle rate, a steering rate, and a vehicle speed measurement each satisfy a threshold requirement and determining if the at least one target is plausible based on the image data and the calculated hitch angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosed subject matter is directed to a system and method for determining target plausibility and may be used in conjunction with a trailer backup assist system employing image based target detection as a means to determine a hitch angle between a tow vehicle and a trailer attached thereto. As exemplarily shown inFIG. 1, an imaging device36is installed in the rear of a tow vehicle12and can be used to image a rear vehicle scene containing a target38on a trailer14. The target38can have a checkered or other pattern and is typically provided in a fixed location on the trailer14so that its position in the imaged scene is dictated by the orientation of the trailer14relative to the towing vehicle12. Thus, by using image based target detection to track the position of the target within the imaged scene, the hitch angle between the vehicle12and trailer14can be determined. In some instances however, image based target detection can fail when the imaging device36images an unreliable target or a false target. In such scenarios, the trailer backup assist system may make an incorrect hitch angle determination. Recognizing this, a system and method is disclosed herein that distinguishes between a plausible target and an implausible target for the purpose of image based target detection.

InFIG. 2, a kinematic model10of a tow vehicle12and trailer14combination is shown having kinematic variables and angles, including a steering angle δ, a trailer length D, and a hitch angle γ, which may be affected by the dynamics of the vehicle12and trailer14combination and representable in kinematic equations. When the hitch angle γ and steering angle δ are substantially constant, the yaw rate of the vehicle12is also substantially constant and equal to the yaw rate of the trailer14. This interaction is used to formulate kinematic equations that can be solved for determining the hitch angle γ between the vehicle12and the trailer14. Specifically, the yaw rate of the vehicle120, as measured by a yaw rate sensor or other onboard vehicle sensor, provides the following equation:

Furthermore, the yaw rate of the trailer can be represented with the following equation:

ⅆβⅆt=vD⁢sin⁢⁢γ+LvDW⁢cos⁢⁢γ⁢⁢tan⁢⁢δ
Where,
δ is the steering angle of the front wheels16of the vehicle12;
D is the length from the hitch point18to the trailer axle20, referred to herein as the hitch to trailer axle length; W is the length from the front axle22of the vehicle12to the rear axle24of the vehicle12, referred to herein as the wheelbase length;
L is the length from the hitch point18to the rear axle24of the vehicle12, referred to herein as the hitch to rear vehicle axle length; and
γ is a hitch angle, as measured between a centerline longitudinal axis26of the vehicle12and a centerline longitudinal axis28of the trailer14.

Accordingly, when the yaw rate of the vehicle12and the trailer14become equal, the hitch angle γ will likely be constant. This condition can occur when a driver attempts to reverse the trailer vehicle12and trailer14in a straight line with the vehicle or when the driver inputs a maximum steering command through a vehicle steering input device such as a steering wheel, a rotatable knob, a touchscreen device, the like, or a combination thereof. In either scenario, the resulting constant hitch angle γ can be described using the following equation:
c=acos γ+bsin γ
This equation can be rewritten as follows:
c=a√{square root over (1−sin2γ)}+bsin γ
The above equation can be rearranged into quadratic form and rewritten as follows:
c2−a2−2bcsin γ+(b2a2)sin γ=0
Solving the quadratic equation for the hitch angle γ yields the following hitch angle equation:

Accordingly, the hitch angle γ may be determined as a function of the hitch to trailer axle length D, the wheelbase length W, the hitch to rear axle length L, and the steering angle δ when the vehicle12and trailer14are reversing and that the yaw rate of the vehicle12and the trailer14are substantially equal during the reversing motion for at least a threshold period of time or over a threshold distance of motion.

Referring toFIG. 3a block diagram is shown of a system30for determining target plausibility. The system30can be combined or in communication with a trailer backup assist system and includes an imaging module32having a controller34and an imaging device36. In one implementation, the imaging device36can be configured to image a target38that is located on the trailer14. Image data generated from the imaging device36can be received and processed by the controller34to produce an image on a display40. The display40can be part of a human machine interface (HMI)41that is implemented in the vehicle12and may include a plurality of user inputs to enable a user to input a variety of commands related to the trailer backup assist system and/or other systems and/or modules onboard the vehicle12.

The controller34can communicate with one or more data collection devices and/or modules configured to receive information corresponding to the hitch angle γ the steering angle δ, and the velocity of the vehicle12. With respect to the illustrated embodiment, the controller34is shown in communication with a hitch angle sensor42, a steering angle sensor44, and a vehicle speed sensor46. The hitch angle sensor42can include mechanical sensor mechanisms or other conceivable hitch angle sensors and can be located on the vehicle12and/or the trailer14. Additionally, the hitch angle sensor42can provide the controller34with hitch angle measurements. The hitch angle measurements can be supplied to the controller34via a communication network of the vehicle12, which can include a controller area network (CAN), a local interconnect network (LIN), or other popular protocols used in the automotive industry. Likewise, the steering angle sensor44and the vehicle speed sensor46can also supply information to the controller34via the communication network of the vehicle12. The steering angle sensor44can be a component of a power steering control module of the vehicle12and can provide the controller34with steering angle measurements. The vehicle speed sensor46can be a component of an engine control module of the vehicle12and can provide the controller34with vehicle speed measurements. Although the abovementioned measurements are described as being received from specific equipment, it should be appreciated that the measurements can be received from any devices implemented by a trailer backup assist system to monitor the kinematic properties of the vehicle12and the trailer14. Furthermore, it should be appreciated that the controller34can be in communication with other equipment used in conjunction with a trailer backup assist system and/or other vehicle system.

As is further shown inFIG. 3, the controller34can include at least one processor48and a memory50storing one or more routines52executable by the processor48. The processor48can be configured to process image data received from the imaging device36and any data received from the hitch angle sensor42, the steering angle sensor44, and the vehicle speed sensor46. Additionally, the processor48can be configured to output one or more signals53based on any of the data inputted from the imaging device36, the HMI41, the hitch angle sensor42, the steering angle sensor44, and/or the vehicle speed sensor46. The outputted signal(s)53can be supplied to a trailer backup assist system and/or other vehicle system to control a function of the vehicle12.

Referring toFIG. 4, a flow diagram of a method54for determining target plausibility is shown. For purposes of illustration, and not limitation, the method54is described as being implemented by system30and can be embodied as a routine52stored in the memory50of the controller34and executable by the processor48. While the steps are described below in a linear manner, it should be appreciated that each step does not necessarily need to be performed in the order in which it is presented and some steps may be omitted altogether. As exemplarily shown inFIG. 4, the method54can begin at step56, where the processor48prompts the imaging device36to image a scene to the rear of the vehicle12. In step58, the processor48analyzes the image data to determine if one or more targets38appear in the imaged scene. If at least one target38is detected, the processor48calculates a hitch angle rate and a steering angle rate in step60using hitch angle measurements and steering angle measurements received from the hitch angle sensor42and the steering angle sensor44, respectively. Optionally, in step62, the processor48can filter the hitch angle rate and the steering angle rate, as calculated in step60, in order to reduce noise. The processor48can also filter a vehicle speed measurement received from the vehicle speed sensor46.

In step64, the processor48checks if a driving condition is satisfied. According to one implementation, the driving condition is characteristic of a moving vehicle having a substantially constant hitch angle γ and steering angle δ. Satisfaction of the driving condition can be determined based on a comparison of the filtered or unfiltered hitch angle rate, steering angle rate, and vehicle speed measurements to associated threshold values, irrespective of whether the vehicle12is moving forward or backward. For example, the driving condition can be satisfied when the absolute value of the hitch angle rate is below a hitch angle rate threshold (e.g. 0.3 degrees/second), the absolute value of the steering angle rate is below a steering angle rate threshold (e.g. 0.3 degrees/second), and the absolute value of the vehicle speed is above a vehicle speed threshold (e.g. 5 km/hour). If the driving condition is satisfied, the processor48calculates a hitch angle γ in step66or otherwise returns to step60. The hitch angle γ can be calculated using the hitch angle equation and based on the steering angle δ received from the steering angle sensor44, the hitch to trailer axle length D, the wheelbase length W, and the hitch to rear axle distance L. The hitch to trailer axle length D, the wheelbase length W, and the hitch to rear axle distance L are generally known values that may be pre-stored to the memory50of the controller34or otherwise inputted and stored to the memory50via a user input device (e.g. HMI41).

In step68, the processor48determines if any of the targets38detected in step58are plausible targets. A target38can be considered plausible if analysis of the image data shows that the position of the target38in the imaged scene is consistent with an expected target position based on the hitch angle γ calculated in step66. When all plausible targets have been determined, the processor48, in step70, can select the one that is most consistently located at the expected target position over a predetermined time period and/or range of calculated hitch angles γ. Consequently, the processor48can directly implement target-related functions (e.g. image based target detection) using the selected plausible target or may instead send a signal (e.g. signal53) to the trailer backup assist system indicating its selection. The trailer backup assist system may then decide whether to use the selected plausible target for target-related functions. If the processor48is unable to determine any plausible targets, the processor48can generate a signal (e.g. signal53) in step72that can be used to notify a vehicle operator that no plausible target has been identified. The notification can be auditory, visual, and/or haptic, and may be implemented via any suitable equipment related to the trailer backup assist system or onboard the vehicle12. Upon the completion of either step70or72, the processor can return to step56to initiate another pass through.

Accordingly, a system and method for determining target plausibility have been advantageously described herein and are generally intended for use with a trailer backup assist system to enable a plausible target to be distinguished from an unreliable or false target for the purpose of image based target detection or other target-related functions.