ADJUSTABLE LIMIT FOR A COLLISION WARNING SYSTEM

Abstract

Device for a vehicle, comprising the following: a driver assistance system that monitors approaching objects around the vehicle and is configured to take a driver assistance action in response to a predicted collision with an approaching object according to a time-to-collision limit; a load monitor that detects whether a trailer is being towed by the vehicle and determines an initial offset in response to a result of the detection, the initial offset being essentially zero if no trailer is detected; a brake monitor that detects a braking force and a resulting change in vehicle speed, determines an expected change in vehicle speed in response to the braking force, and selects a second offset in response to a braking difference between the resulting speed change and the expected speed change, wherein the second offset is essentially zero if the braking difference is below a braking threshold; a steering monitor that detects a steering angle of the vehicle and a resulting change in the vehicle yaw rate, determines an expected change in the vehicle yaw rate in response to the steering angle, and selects a third offset in response to a steering difference between the resulting yaw rate change and the expected yaw rate change, wherein the third offset is essentially zero when the steering difference is below a steering threshold; an updater that determines an order of magnitude of the time-to-collision limit in response to the first, second, and third offsets.

Description

[0001] The present invention relates generally to collision warning and avoidance systems for motor vehicles and more specifically to an adjustable threshold for initiating driver assistance measures in response to predicted collisions.

[0002] Several different types of driver assistance systems have been developed that involve the remote detection and tracking of other vehicles or objects approaching or potentially colliding with a host vehicle. Scanning radar systems, camera-based optical detection systems, or combinations of the two are typically used to locate relevant objects, determine their relative speed and trajectory, and predict if and when a collision might occur if the vehicles remain on their current paths. The driver assistance system can simply warn the driver, as in a forward collision warning system (FCW system), allowing the driver to determine and execute any necessary evasive maneuvers.Other types of driver assistance systems, such as an adaptive cruise control system (ACC system), can automatically initiate an evasive action by reducing a set cruising speed when a vehicle ahead is detected, or such as a brake steering system, which can apply unequal braking forces to different wheels to steer the host vehicle away from a potential collision.

[0003] German patent application DE 10 2012 101 954 A1 describes a vehicle assistance device for collision prevention by means of automatic braking intervention. Measures are triggered depending on the time remaining until a collision, with the respective measure being determined by comparison with various time limits.

[0004] German patent application DE 10 2012 111 846 A1 discloses a collision avoidance system and a collision avoidance procedure for vehicles for triggering a warning signal and / or a driving maneuver in the event of a risk of collision with an object. The selection of a collision avoidance measure is made by comparing the time interval until a potential collision with various limit values.

[0005] The initiation of a driver assistance action (whether it's issuing a warning or automatically intervening to avoid a predicted collision) may or may not be triggered depending on how imminent a potential collision actually is. In a typical FCW system, a time-to-collision threshold is used to determine whether a potential collision is sufficiently imminent to warrant a warning. The threshold is based on the current host vehicle speed and the relative approach speed of the target on the collision course. The threshold is usually defined in terms of the estimated time that would elapse until the predicted collision. The time for the threshold is typically longer if the host vehicle is traveling at higher speeds.Using the predefined time limit and the relative approach speed of the target, a warning is generated when the target approaches the host vehicle within a distance equal to the relative speed divided by the limit.

[0006] The length of the time-to-collision threshold is generally predetermined by the vehicle manufacturer to give the driver sufficient opportunity to take any necessary evasive action while ensuring that unnecessary warnings are not generated. The selection of a time-to-collision threshold depends on various parameters and driving conditions that presuppose a certain nominal performance characteristic of the host vehicle, such as braking and steering performance, vehicle weight, and others. The threshold settings are also based on assumptions regarding typical road conditions, weather, and other environmental variables. The resulting thresholds generally provide good overall performance for most situations.However, vehicle parameters change as a vehicle ages, and weather or road conditions can frequently change in ways that affect the time required to effectively execute an evasive maneuver. For example, variable road surface conditions resulting from precipitation, temperature, a rough surface, or sand or gravel covering the road can increase the time needed to slow down or steer a vehicle. Various factors, such as tire wear, can also affect surface friction and the ability to generate the torque needed to slow down or steer. Consequently, a situation where a two-second time-to-collision threshold would be adequate under normal conditions may prove insufficient if particularly adverse conditions prevail.It would be desirable to increase the time-to-collision limit to better align it with the actual conditions that affect the maneuverability of the host vehicle.

[0007] In one aspect of the invention, a device for a vehicle is provided which includes a driver assistance system that monitors approaching objects around the vehicle and is configured to take a driver assistance action in response to a predicted collision with an approaching object according to a time-to-collision threshold. A load monitor detects whether a trailer is being towed by the vehicle and determines a first offset in response to the result of the detection, the first offset being essentially zero if no trailer is detected.A brake monitor detects a braking force and a resulting change in vehicle speed, determines an expected change in vehicle speed in response to the braking force, and selects a second offset in response to a braking difference between the resulting speed change and the expected speed change, with the second offset being essentially zero if the braking difference is below a braking threshold.A steering monitor detects the vehicle's steering angle and the resulting change in the vehicle's yaw rate. It determines an expected change in the vehicle's yaw rate in response to the steering angle and selects a third offset in response to any steering differential between the resulting and expected yaw rate changes. This third offset is essentially zero if the steering differential is below a steering threshold. An updater determines the order of magnitude of the time-to-collision threshold in response to the first, second, and third offsets. Fig. Figure 1 shows a host vehicle tracking several target vehicles in the vicinity. Fig. Figure 2 shows a variable penetration zone around a host vehicle resulting from a variable time-to-collision threshold. Fig. Figure 3 is a block diagram showing a preferred embodiment of a vehicle according to the present invention. Fig. Figure 4 is a flowchart showing a preferred method of the invention. Fig. Figure 5 shows a lookup table for determining an offset based on a trailer class that can generate a load for the host vehicle. Fig. Figure 6 shows a lookup table for determining expected deceleration, assuming nominal driving conditions, according to various combinations of braking force and host vehicle speed. Fig. Figure 7 shows a relationship between a limit offset and a difference between actual deceleration and expected deceleration. Fig. Figure 8 shows a relationship between a limit offset and a difference between an actual yaw rate change and an expected yaw rate change during a steering maneuver.

[0008] The present invention assesses current driving conditions using systems and sensors that are typically already present in a vehicle. The parameters investigated include vehicle load (e.g., number of passengers, cargo, towing a trailer, etc.) and vehicle-road interactions (e.g., changes in friction resulting from tire wear, brake wear, rough road surfaces, and surface debris). Information gathered from these parameters is used to determine whether default settings, such as the time-to-collision threshold, should be modified in the driver assistance system (e.g., forward collision warning system, adaptive cruise control, or brake-steering system).

[0009] Now, with reference to Fig. 1 is a host vehicle 10 traveling on a multi-lane roadway, equipped with a remote vehicle detection and tracking system 12. Within a field of view 13, the tracking system 12 monitors target vehicles 14, 15, and 16. For each tracked object, a set of parameters characterizing the nature and behavior of each object is determined and made available for use by other systems. For example, a parameter set 17 is generated for target vehicle 14 and a parameter set 18 is generated for target vehicle 15, each potentially consisting of a distance, direction, relative speed, absolute speed, and travel path of the vehicle, etc.

[0010] The vehicle 10 also features a driver assistance system (DAS) 20, which receives parameter sets 17 and 18 in an object list received from a tracking system 12. Depending on the specific purpose of the driver assistance system 20, different driver assistance measures can be taken according to the proximity of any relative approaching target vehicles. The assistance system 20 can examine parameters such as the distance, direction, relative speed, and / or trajectory of the target vehicle, as received from the tracking system 12, to identify whether each tracked vehicle is on a collision course and, if so, the estimated time until collision. The assistance system 20 can define an intrusion zone to determine when a driver assistance measure should be taken in response to a relative approaching object on a collision course.

[0011] As in Fig. As shown in Figure 2, the intrusion zone can be defined in terms of a time-to-collision threshold, which is set as a time reflecting driver or control system reaction time and other representative performance factors. A time-to-collision threshold 21 with a value of 2 seconds produces a smaller intrusion zone than a time-to-collision threshold 22 with a value of 3 seconds. The actual size of an intrusion zone depends on the relative approach speed of the target object on a collision course. However, in conventional driver assistance systems, time-to-collision threshold values ​​have been based on a fixed set of driving conditions, such as vehicle load and vehicle-road interactions, even though these conditions are not static.

[0012] A vehicle device for dynamically updating a time-to-collision limit is in Fig. Figure 3 shows a vehicle 25 equipped with a remote object detection and tracking system 26, which includes a sensor 27 (such as an electronic scanning radar) and an object tracking controller 28. Tracked objects are reported to a driver assistance system 30, which monitors the objects and can initiate a driver assistance action using an actuator 31.

[0013] In one embodiment, the FAS system 30 can consist of a forward collision warning system (FCW system), wherein the actuator 31 includes a perceptible warning generator, such as an audio speaker that produces warning tones, or an optical indicator element for generating a flashing light or a message. The perceptible warning signal alerts the driver of the predicted collision so that the driver can take evasive action. Alternatively, the FAS 30 can consist of an adaptive cruise control system (ACC system), wherein a driver assistance action taken by the actuator 31 can involve reducing a commanded speed set by the ACC system to prevent a collision with a target vehicle encountered in the path of the host vehicle. The ACC system can also optionally generate a perceptible warning signal.In yet another embodiment, the FAS system 30 can have a brake-steering system, wherein the driver assistance measure involves the application of a braking force in an unbalanced manner to the individual wheels in order to steer the vehicle in such a way as to avoid the predicted collision.

[0014] Every other type of driver assistance system can generally employ intrusion zones of varying dimensions, corresponding to their different types of functions. However, in each case, the specified limits have not previously taken into account the variability of driving conditions, which can negatively affect maneuverability, to change the speed or direction of the host vehicle in order to avoid a potential collision. Consequently, the vehicle 25 employs an update module 35 to monitor various aspects of the driving conditions and update the time-to-collision limit used by the ADAS 30. In the embodiment shown, conventionally defined time-to-collision limits include default values ​​stored in a standard memory block 36. The default values ​​are provided to an updater block 37, which uses various offsets (i.e.,The system receives increments, as described below, which are added to the standard value and provided to the FAS 30 as the adjusted threshold. Each of the separate aspects of the driving conditions described below represents a deterioration or decrease in vehicle maneuverability. Consequently, each provides an incremental offset to be added to the standard threshold to increase the magnitude of the threshold time and thereby enlarge the corresponding intrusion zone (the violation of which triggers the driver assistance action). Similarly, these additions are revised or removed if the vehicle conditions (e.g., replacement of worn tires) or driving conditions change.

[0015] A primary aspect of the driving conditions is the vehicle load (i.e., the mass carried by the vehicle). A load monitor 40 can assess various aspects of the load, including whether the vehicle 25 is currently towing a trailer 41. This detection can be achieved by monitoring the status of a trailer connection 42. Consequently, if the trailer 41 is present, current flow through the connector 42 can be checked to determine the presence of the trailer 41. Furthermore, the load monitor 40 can determine the class or size of the connected trailer in various ways, such as by identifying the type of connector present (e.g., a four-pin connector for a small trailer or a seven-pin connector used by larger trailers).If no trailer is detected, the offset provided by the load monitor 40 to the updater 37 is essentially zero.

[0016] The update module 35 also includes a brake monitor 43, which monitors braking performance in such a way as to reveal any decrease in the rated braking performance, which is the basis for the standard values. The brake monitor 43 determines braking force using one or more sensors 44, such as a brake pedal sensor to indicate the magnitude of the brake pedal movement. The brake monitor 43 also detects any change in vehicle speed resulting from the braking event with the detected braking force. The brake monitor 43 can be coupled to an engine control unit (ECU) 45 to determine any desired parameters related to vehicle speed. The speed-related change could be, for example, a deceleration value, an actual decrease in speed, or a distance traveled during a specific unit of time.The brake monitor 43 further determines an expected change in the vehicle speed-related parameter that would occur under the nominal driving conditions. The brake monitor 43 determines a difference between the changes related to the actual and the expected speed and selects a limit offset (i.e., increment) in response to the difference. If the braking difference is below a predefined braking difference limit, the offset is preferably essentially zero. For larger differences, a higher offset is added to the time-to-collision limit according to a monotonically increasing function stored by the brake monitor 43.

[0017] The update module 35 also includes a steering monitor 46, which responds to any driving conditions that negatively affect the host vehicle's ability to steer away from a potential collision. The steering monitor 46 detects the vehicle's steering angle via a connection to one or more sensors 47, such as a steering wheel angle sensor. The steering monitor 46 further determines a resulting change in the vehicle's yaw rate (i.e., the lateral acceleration resulting from a steering angle that should cause the vehicle to veer sideways). The steering monitor 46 also determines an expected change in the vehicle's yaw rate based on the detected steering angle and other parameters, such as the current vehicle speed. Yaw rate signals can be obtained from the engine control unit (ECU) 45 or directly from a yaw rate sensor integrated into the sensors 47.The steering monitor 46 selects an offset in response to a difference between the measured yaw rate change and the expected yaw rate change. If the steering difference is below a steering threshold, the offset is essentially zero. For differences above the steering threshold, the updater 37 is provided with a monotonically increasing offset.

[0018] The update module 35 further includes a traction monitor 48, which is coupled to the MSG 45 and / or additional sensors, for determining wheel speeds at at least one driven wheel and at least one non-driven wheel. The traction monitor 48 detects a mismatch between the speed of the driven wheel and the speed of the non-driven wheel. It also determines a torque applied to the driven wheel to determine an expected mismatch in response to the torque. The applied torque is preferably available from the MSG 45. The traction monitor 48 selects an offset in response to the difference between the detected wheel speed mismatch and the expected mismatch. If the difference is below a traction threshold, the offset is essentially zero.Above the limit value, a monotonically increasing offset is generated and provided to updater 37.

[0019] In a preferred embodiment, the updater 37 generates a sum of a nominal limit value determined from the standard block 36, plus the offsets received from the load monitor 40, the brake monitor 43, the steering monitor 46, and the traction monitor 48. Alternatively, the updater 37 could receive the differences between the actual and expected performance directly from each monitor and use them to identify an appropriate time-to-collision limit value from a model that incorporates the standard values.

[0020] A preferred method of the invention is described in Fig. Figure 4 shows that a limit value update routine is initialized in step 50 with the default settings for the time-to-collision limit. The process then runs periodically to adjust the limit value to changing conditions while the vehicle is driving. In step 51, a check is performed to determine if a trailer is detected. If so, an offset based on the trailer class is selected in step 52. If no unusual load conditions exist (i.e., no trailer is detected), the process proceeds to the next aspect of the driving conditions. Consequently, a check is performed in step 53 to determine if the vehicle is braking. If the vehicle is not braking during the current process, the next aspect is examined in step 57.While the vehicle is braking, a braking level or braking force is obtained in step 54, and the resulting change in speed is measured in step 55. In step 56, the braking force is used to determine an expected change in speed, and the difference between the measured and the expected change in speed is used to select an offset to increase the time-to-collision threshold.

[0021] Step 57 checks if the vehicle is currently turning. If so, the steering angle is obtained in step 58, and a resulting yaw rate change is measured in step 60. In step 61, an expected yaw rate change for nominal driving conditions is determined based on the steering angle and other parameters, such as vehicle speed, and the difference between the measured and expected yaw rate changes is used to select an offset. In step 62, a check is performed to determine if the vehicle is moving (i.e., being driven as a result of the torque applied to the wheels). If so, individual wheel speeds are measured in step 63, and the applied torque is obtained. Based on the expected differences between the speeds of a driven and a non-driven wheel at the applied torque, a value for the offset is selected in step 64.

[0022] In step 65, each of the offsets received from the various monitors is applied to the default settings. If the resulting magnitude of the time-to-collision threshold has changed from the previously used value, the driver assistance system is updated accordingly in step 66.

[0023] Fig. Figure 5 presents a table, which can be stored in a load monitor, for correlating a detected trailer plug with a corresponding order of magnitude for the respective offset. Consequently, a small trailer with a four-pin plug results in an offset of i1 seconds, while a larger trailer of the seven-pin class produces an offset of i2 seconds.

[0024] Fig. Figure 6 shows a table stored in the brake monitor that can be used to determine an expected change related to speed. Consequently, rows in the table represent respective ranges of braking force or braking level (as a percentage of full braking). The table columns represent respective ranges R1–R4 of the initial vehicle speed. The table cells contain respective values ​​D1 to D1. 16for the expected deceleration or speed reduction. These values ​​can be pre-calibrated by the vehicle manufacturer by measuring the speed reductions or deceleration that result under nominal conditions when specific braking forces are applied to predetermined ranges of initial speed. After taking a difference between the expected deceleration from a given cell and the measured deceleration, the difference is used to obtain an offset value using a transfer function, as in Fig. Figure 7 shows that up to a braking limit 70, a transfer function 71 can have a value of zero along a segment 72. As the braking differential increases, the offset value increases along a segment 73 until a maximum is reached at a segment 74. The slope and / or shape of the transfer function 71 is vehicle-specific and can vary according to various parameters of a vehicle design, but preferably increases monotonically between the zero value and the maximum value.

[0025] Fig. Figure 8 shows another example of a transfer function, where a yaw rate difference is used to generate an offset value that has a zero value below a yaw rate limit of 75 and then monotonically increases to a maximum value.

[0026] By basing the time-to-collision threshold used by the driver assistance system on actual vehicle driving conditions and vehicle usage, the present invention ensures that a driver is alerted in time to react to a potential collision and is better able to avoid the potential collision.

Claims

[1] Device for a vehicle comprising the following: a driver assistance system that monitors approaching objects around the vehicle and is configured to take a driver assistance action in response to a predicted collision with an approaching object according to a time-to-collision limit; a load monitor that detects whether a trailer is being towed by the vehicle and determines an initial offset in response to a result of the detection, the initial offset being essentially zero if no trailer is detected; a brake monitor that detects a braking force and a resulting change in vehicle speed, determines an expected change in vehicle speed in response to the braking force, and selects a second offset in response to a braking difference between the resulting speed change and the expected speed change, wherein the second offset is essentially zero if the braking difference is below a braking threshold; a steering monitor that detects a steering angle of the vehicle and a resulting change in the vehicle yaw rate, determines an expected change in the vehicle yaw rate in response to the steering angle, and selects a third offset in response to a steering difference between the resulting yaw rate change and the expected yaw rate change, wherein the third offset is essentially zero when the steering difference is below a steering threshold; an updater that determines an order of magnitude of the time-to-collision limit in response to the first, second, and third offsets. [2] Device according to claim 1, wherein the updater determines the order of magnitude of the time-to-collision limit according to a sum of a nominal limit for the vehicle and the first, second and third offsets. [3] Device according to claim 1, further comprising: a traction monitor that detects a mismatch between the speed of a driven wheel and the speed of a non-driven wheel, determines a torque applied to the driven wheel, determines an expected mismatch in response to the determined torque and selects a fourth offset in response to a difference between the detected wheel speed mismatch and the expected mismatch, wherein the fourth offset is essentially zero if the difference between the detected mismatch and the expected mismatch is below a threshold value; where the updater determines the order of magnitude of the time-to-collision limit in response to the first, second, third, and fourth offsets. [4] Device according to claim 1, wherein the driver assistance system includes a collision warning system and wherein the driver assistance measure consists of a perceptible warning signal to alert the driver of the predicted collision. [5] Device according to claim 1, wherein the driver assistance system includes an adaptive cruise control system and wherein the driver assistance measure consists of reducing a commanded speed of the adaptive cruise control system in order to avoid the predicted collision. [6] Method for adapting a driver assistance system that monitors approaching objects around the vehicle and is configured to take a driver assistance action in response to a predicted collision with an approaching object according to a time-to-collision limit, the method comprising the following steps: Detect whether a trailer is being towed by the vehicle; Determining an initial offset in response to a detection result, wherein the initial offset is essentially zero if no follower is detected; Detecting braking force and the resulting change in vehicle speed; Determining an expected change in vehicle speed in response to braking force; Selecting a second offset in response to a braking difference between the resulting velocity change and the expected change Speed ​​change, where the second offset is essentially zero if the braking difference is below a braking threshold; Detecting the vehicle's steering angle and the resulting change in the vehicle's yaw rate; Determining an expected change in the vehicle yaw rate in response to the steering angle; Selecting a third offset in response to a steering difference between the resulting yaw rate change and the expected yaw rate change, wherein the third offset is essentially zero when the steering difference is below a steering threshold; Determining an order of magnitude of the time-to-collision limit in response to the first, second, and third offsets. [7] Method according to claim 6, wherein the step of determining an order of magnitude of the time-to-collision limit includes forming a sum of a nominal limit for the vehicle and the first, second and third offset. [8] The method of claim 6, further comprising the following steps: Detecting a mismatch between the speed of the driven wheel and the speed of the non-driven wheel; Determining a torque applied to the driven wheel; determining an expected mismatch in response to the determined torque and Selecting a fourth offset in response to a difference between the detected mismatch and the expected mismatch, wherein the fourth offset is essentially zero if the difference between the detected mismatch and the expected mismatch is below a threshold; where the step of determining an order of magnitude of the time-to-collision limit involves forming a sum of a nominal limit for the vehicle and the first, second, third and fourth offsets. [9] Method according to claim 6, wherein the driver assistance system includes a collision warning system, the method further comprising the following step: Generating a noticeable warning signal to alert the driver of the predicted collision. [10] Method according to claim 6, wherein the driver assistance system includes an adaptive cruise control system, the method further comprising the following step: Reducing a commanded speed of the adaptive cruise control system, to avoid the predicted collision.

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