Abstract:
In one aspect, the invention is directed to an adaptive cruise control system for a host vehicle, comprising a long-range sensor configured to determine a location of objects positioned ahead of the host vehicle, at least one short-range sensor configured to determine the location of objects in close proximity ahead of the host vehicle, and a controller configured to receive information from the long-range sensor and from the at least one short-range sensor and to control the speed of the host vehicle based at least in part thereon, wherein the controller is configured to operate the at least one short-range sensor in a plurality of operating modes, and to select a short-range sensor operating mode at least in part in response to the location of any objects detected by the long-range sensor.

Description:
[0001]    This application claims the benefits of U.S. Provisional Application No. 61/042,924, filed Apr. 7, 2008. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention generally relates to an automotive cruise control system, and more particularly, to a full speed range cruise control system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Traditional automotive cruise control systems maintain a user selected set-speed without any regard for traffic. In recent years adaptive cruise control (ACC) systems have entered the market, which utilize long-range sensing systems, e.g. 77 GHz radar systems or Lidar systems, to detect vehicles preceding the host vehicle. Based on detected preceding vehicles the adaptive cruise control systems adjusts the host vehicle speed to either the user selected set-speed or a safe following speed, whichever is lower. Ideally, a vehicle with engaged adaptive cruise control system can follow other vehicles in congested driving scenarios without a need for the driver to accelerate or decelerate manually. 
         [0004]    Adaptive cruise control systems however require a minimum activation speed and automatically disengage when the host vehicle slows down below a deactivation speed. Given these limitations adaptive cruise control systems are generally limited to highway driving where the host vehicle does not come to a complete stop. 
         [0005]    More recently follow-to-stop ACC systems, also called “full speed range ACC” or “Stop and Go ACC” have been suggested. The problem however is, that follow-to-stop ACC systems require much more accurate short-range sensing capability than traditional ACC systems. The accuracy requirement for follow-to-stop ACC exceeds the capability of traditional long-range sensing systems. Also, long-range sensors often utilize a narrow vertical opening angle to concentrate their transmitted energy on distant targets. Some vehicles, for example school buses or certain trailers, however have a rear end reaching high above the road. This can cause traditional long-range sensors to not detect the rear end of a vehicle but rather the rear axle of the preceding vehicle, leading to substantial measurement error. This problem and attempts to overcome it have been described in US200510159875, which is hereby incorporated by reference thereto. 
         [0006]    Also, traditional cruise control systems have a relatively narrow field of view of only 12-16 degrees. While this is sufficient to detect distant vehicles in the same and neighboring lanes it is insufficient to e.g. detect a pedestrian walking up in front of the host vehicle, expecting it to come to a complete stop before reaching the pedestrian. 
         [0007]    Automotive parking aid systems have long been using ultrasonic short-range sensors to help the driver estimate distance from other vehicles while parking. Known park assist systems however require relatively long time to detect objects, making them not suitable for follow-to-stop ACC systems which depend on quick reaction while the vehicle is still moving. 
         [0008]    Therefore, in light of the problems associated with existing approaches, there is a need for improved follow-to-stop adaptive cruise control systems that eliminate the shortfalls associated with traditional ACC sensing systems. 
       SUMMARY OF THE INVENTION 
       [0009]    In one aspect, the invention is directed to an adaptive cruise control system for a host vehicle, comprising a long-range sensor configured to determine a location of objects positioned ahead of the host vehicle, at least one short-range sensor configured to determine the location of objects in close proximity ahead of the host vehicle, and a controller configured to receive information from the long-range sensor and from the at least one short-range sensor and to control the speed of the host vehicle based at least in part thereon, wherein the controller is configured to operate the at least one short-range sensor in a plurality of operating modes, and to select a short-range sensor operating mode at least in part in response to the location of any objects detected by the long-range sensor. 
         [0010]    In another aspect, the invention is directed to an adaptive cruise control system for a host vehicle, comprising a long-range sensor configured to determine a location of vehicles located ahead of the host vehicle, at least one short-range sensor configured to determine the location of objects in close proximity ahead of the host vehicle, a controller configured to receive information from the long-range sensor and from the at least one short-range sensor and to control the speed of the host vehicle based thereon. The vertical opening angle of the at least one short-range sensor is larger than the vertical opening angle of the long-range sensor. 
         [0011]    In another aspect, the invention is directed to an adaptive cruise control system for a host vehicle, comprising a long-range locating system configured to determine a location of vehicles located ahead of the host vehicle and at least one short-range sensor configured to determine the location of objects in close proximity ahead of the host vehicle. The short-range sensor is deactivated if the host vehicle exceeds a predetermined speed threshold. 
         [0012]    In another aspect, the invention is directed to a method for locating objects in front of a host vehicle comprising:
       synchronously transmitting ultrasonic pulses from a plurality of ultrasonic sensors, measuring the time of flight of ultrasonic reflections received by the ultrasonic sensors,   calculating the distance of objects based on the measured times of flight,   capturing an image of a scene in front of the vehicle, and   correlating the distance of objects detected by the ultrasonic sensors with objects extracted from the image of the scene in front of the vehicle.       
 
         [0017]    In another aspect, the invention is directed to an adaptive cruise control system for a host vehicle, comprising a long-range locating system configured to determine a location of vehicles located ahead of the host vehicle and at least one short-range sensor configured to determine the location of objects in close proximity ahead of the host vehicle, wherein the short-range sensor is deactivated if the host vehicle exceeds a predetermined speed threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention will now be described by way of example only with reference to the attached drawings, in which: 
           [0019]      FIG. 1  is a plan view of a host vehicle with an adaptive cruise control system in accordance with an embodiment of the present invention; 
           [0020]      FIG. 2   a  is a simplified schematic diagram of a selected electrical components in the adaptive cruise control system shown in  FIG. 1 ; 
           [0021]      FIG. 2   b  is a more detailed schematic diagram of the selected electrical components shown in  FIG. 2   a;    
           [0022]      FIGS. 3   a  and  3   b  illustrate the operation of ultrasonic sensors shown in  FIG. 2   b , in a first mode of operation; 
           [0023]      FIGS. 4   a  and  4   b  illustrate the operation of the ultrasonic sensors shown in  FIGS. 3   a  and  3   b , in a second mode of operation; 
           [0024]      FIGS. 5   a  and  5   b  illustrate the operation of the ultrasonic sensors shown in  FIGS. 3   a  and  3   b , in a third mode of operation; 
           [0025]      FIG. 6  is an illustration of the relationship between several modes of operation of the ultrasonic sensors shown in  FIG. 2   b  and the speed of the vehicle shown in  FIG. 1 ; 
           [0026]      FIG. 7   a  is an elevation view of the vehicle shown in  FIG. 1  at a first distance to a preceding vehicle; and 
           [0027]      FIG. 7   b  is an elevation view of the vehicle shown in  FIG. 1  at a second, closer distance to a preceding vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Reference is made to  FIG. 1 , which shows a host vehicle  10  with a full speed range adaptive cruise control system  12 , which may also be referred to as a follow-to-stop adaptive cruise control system, in accordance with an embodiment of the present invention. Selected electrical components from the adaptive cruise control system  12  are shown in a simplified format in  FIG. 2   a . The adaptive cruise control system  12  includes a main controller  14  which may be referred to as a fusion controller, a fusion module or a fusion processing module, an engine controller  16 , a brake controller  18 , and a plurality of sensors  19 , including a camera  20 , a long-range sensor  22  and a plurality of short-range sensors  24  that are part of a short-range sensing system  25 . The main controller  14  sends instructions to the engine controller  16  and to the brake controller  18  (ie. the main controller  14  is operatively connected to the engine and brake controllers  16  an  18 ) based on input from the camera  20 , the long-range sensor  22  and short-range sensors  24 , and based on input from in-cabin controls (not shown) permitting the vehicle driver to take such actions such as turning the adaptive cruise control system  12  on or off and to set a maximum speed for the host vehicle  10 . 
         [0029]    The long-range sensor  22  may be a radar sensor operating at 24 or 77 GHz, a Lidar sensor, or any other suitable distance measuring sensor that is suitable to detect vehicles and other objects in front of the host vehicle  10 . A 24 GHz frequency modulated continuous wave (FMCW) sensor, shown at  80  in  FIG. 2   b , having an object detection range of about 120 m is an example of a suitable long-range sensor  22 . Referring to  FIG. 2   b , the FMCW sensor  80  may include a transmitter  82  and one or more receivers  84 , an RF signal processor and controller  86 , a power supply  88  that is connected to a power source (not shown) and to ground (not shown), an a/d converter  90 , a digital signal processor  92  and a CAN interface  94 , which connects with a corresponding CAN interface  96  on the fusion controller  14 . 
         [0030]    The camera  20  may be any suitable type of camera, such as a monocular camera. The camera  20  may be a multi-functional, forward-facing camera employing image processing techniques to analyze a scene of the road in front of the host vehicle  10  in order to detect lane markings and other objects such as cars, trucks, buses, motorcycles, bicycles and pedestrians. Referring to  FIG. 2   b , the camera  20  may include a lens  98 , an imager  100  such as a high dynamic range RCCC (Rate-Constrained Coder Control) imager, a power supply  102 , an oscillator  104  and an LVDS (Low-voltage differential signal) transmitter  106  that communicates with a video interface  111  (ie. an LVDS receiver) on the fusion controller  14 . 
         [0031]    In the exemplary embodiment there are four short-range sensors, shown individually at  24   a ,  24   b ,  24   c  and  24   d , provided in the short-range sensing system  25 , however it will be appreciated that a greater or smaller number of short-range sensors  24  may be provided based on factors such as, for example, the width of the host vehicle  10  incorporating the cruise control system  12 . The short-range sensors  24  may be any suitable type of sensors, such as piezo-electric ultrasonic sensors. Thus, the short-range sensors  24  may be referred to as ultrasonic sensors and the short-range sensing system  25  may be referred to as the ultrasonic sensing system  25 . The ultrasonic sensors  24  may be part of a front park assist system with a range of about 2-3 meters. To avoid blind spots the ultrasonic sensing system may use 2 or more ultrasonic transmitter-and-sensing elements located in the front of the host vehicle  10 , e.g. integrated into a front bumper. 
         [0032]    The sensors  19  in the exemplary follow-to-stop adaptive cruise control system  12  may comprise internal data processing circuitry to track objects over time, in which case they may be referred to as ‘smart’ sensors. Such ‘smart’ sensors may communicate a processed list of objects including, if available, the objects&#39; relative location to the host vehicle  10 , estimated distance and angle of the objects relative to the host vehicle  10 , object classification and other relevant information through a serial data bus for further processing. Alternatively, ‘dumb’ sensors may only include basic signal analysis processing and provide a snapshot of targets to a central processing module for further analysis. Different sensor types may be mixed, e.g. a ‘smart’ radar long-range sensor  22  may be used in combination with ‘dumb’ ultrasonic sensors  24 . 
         [0033]    Smart sensors  19  may receive object information from the other sensors  19  to refine their object tracking and classification. Information from all sensors  19  may be received by a central fusion processing module (ie. the main controller  14 ) which combines the information from the different sensors  19  to derive a more accurate map of objects around the host vehicle  10  than is available from each sensor  19  individually. Based on the object map around the host vehicle  10  the fusion module  14  may send acceleration and deceleration commands to other vehicle components, e.g. the engine controller  16  and the brake controller  18 , through a serial data network. The fusion module  14  may be part of an existing powertrain or chassis control system. Additionally, the fusion controller  14  may receive and process signals from a rearview camera, shown at  110 , which may be used as a backup assist camera. 
         [0034]    The fusion module  14  may attribute different weights to information received from the various sensors  19  based on weighting factors. The radar sensor  22  may, for example, provide very accurate relative velocity information by measuring the Doppler shift in the radar echo of an object, while the camera  20  estimates relative velocity relatively less accurately, based on movement of the object&#39;s base point and size in the image viewed and analyzed by the camera  20 . The weighting factors need not be constant but can be adjusted based on factors, such as, for example, distance of the object to the host vehicle  10 , the speed of the host vehicle  10 , weather and exterior lighting (day/night). More specifically, the ultrasonic short range distance sensing system  25  may, for example, only be used when the speed of the host vehicle  10  is below a threshold. The ultrasonic sensing system  25  may be turned off if the host vehicle  10  exceeds a first speed threshold speed Voff and turned on if the speed of the host vehicle  10  falls below a second speed threshold Von. The first speed threshold Voff may be higher than the second speed threshold Von, which means that, when the ultrasonic sensing system is on it may not go off until the host vehicle  10  rises above the threshold speed Voff, and once the ultrasonic sensing system  25  is off it may not go on until the host vehicle  10  drops below the second threshold speed Von. Alternatively, the first and second threshold speeds Von and Voff may be the same speed. 
         [0035]    Referring to  FIG. 2   b , the fusion controller  14  includes a main control board  112 , a processor  113 , and other hardware such as the video interface  111  for communication with the forward-facing camera  20 , a video interface  114  for communicating with the rearview camera  110 , a power supply  116 , the CAN interface  96  for communicating with the long-range sensor  22 , a CAN interface  118  for communicating with other vehicle components, a LIN (local interconnect network) interface  120  for connecting to the short-range sensors  24  and another LIN interface  122  for connecting to short-range sensors  124  at the rear of the host vehicle  10 , which may be used as part of a backup/parking assist system. 
         [0036]    The ultrasonic short-range sensing system  25  may operate in different operating modes. In a first operating mode, which may be referred to as the A-A mode and which is illustrated in  FIGS. 3   a  and  3   b , a short ultrasonic pulse shown at  26  in  FIG. 3   a  may be emitted by one of the two or more ultrasonic sensors  24 , such as by sensor  24   b . If an object is present in front of the host vehicle  10 , the pulse  26  will be reflected off the object, which is shown at  30 . The same sensor  24   b  may then be used to detect the reflected pulse  26 . Based on the time of flight between emitting the pulse  26  and the detection of the reflected pulse  26 , the distance of the closest object  30  from the sensor  24   b  may be derived. 
         [0037]    In a second operating mode, illustrated in  FIGS. 4   a  and  4   b  and which may be referred to as the A-B mode, one of the ultrasonic sensors, such as sensor  24   b , may transmit an ultrasonic pulse shown at  34  ( FIG. 4   a ) while one or more of the other sensors  24 , such as sensors  24   a ,  24   c  and  24   d , detects the ultrasonic reflection, also shown at  34  from the object  30  ( FIG. 4   b ). 
         [0038]    In a third mode, illustrated in  FIGS. 5   a  and  5   b , and which may be referred to as “synchronous mode” all ultrasonic sensors  24  may transmit ultrasonic pulses (shown at  40 ) simultaneously and then listen to reflections of the pulse  40  in parallel. 
         [0039]    Each ultrasonic sensor  24  may operate at a frequency of about 51 kHz. To detect objects that are further away from the host vehicle a long ultrasonic pulse of about 20 cycles may be used. To detect object very close to the host vehicle a short ultrasonic pulse of about 8 cycles may be used. 
         [0040]    Traditional ultrasonic parking sensors operate by alternating between short and long pulses and switch between A-A and A-B modes based on a fixed pattern. While the traditional operating mode is suitable to aid the driver at parking a vehicle the resulting overall system latency is relatively long (eg. up to approximately 500 msec). 
         [0041]    Preferably when used in embodiments of the present invention, the ultrasonic sensor system  25  has a latency of around 50 msec. One way of providing a reduced latency, as compared with how the ultrasonic sensors  24  may be used in a park-assist system, is to eliminate short pulses (eg. the pulses of 8 cycles). Such pulses may be of assistance to detect objects in very close proximity to the host vehicle  10 , but may be of relatively lower value during at least some stages of following a target vehicle to a full stop. As the host vehicle  10  slows down following a leading vehicle to a complete stop the distance of the leading vehicle may have already been determined by the long-range sensor  22  and the camera  20 . The ultrasonic sensors  24  may be activated based on an activation speed threshold Von or based on information derived from the other sensors  19  that an object has entered or is about to enter the area covered by the ultrasonic sensors  24 . In one embodiment, if the speed of the host vehicle  10  falls below a second, lower, speed threshold, short pulses (eg. of 8 cycles) may be used. While threshold speeds have been described to switch between different ultrasonic sensor operating modes more sophisticated approaches are possible. The fusion module  14  may, for example, based on information received from all sensors  19  over time create a map of objects around the host vehicle  10  and based on the host vehicle  10  approaching an object decide to utilize short ultrasonic pulses for added ultra-short-range sensing. 
         [0042]    Another way of reducing ultrasonic sensing latency is to transmit ultrasonic pulses synchronously from two or more ultrasonic sensors  24  (as shown in  FIG. 5   a ). By using synchronous transmission of ultrasonic pulses from several sensors the ability to triangulate the location of an object is lost, however. In a traditional park-assist application, triangulation may be used to distinguish between objects directly ahead of the host vehicle  10  and those slightly to the side of the host vehicle  10 . Within the follow-to-stop ACC system  12  the camera  20  may be provided with accurate lateral resolution, so that the inability to triangulate during synchronous mode to obtain positional information on an object can be compensated for by deriving the positional information from the images input received by the camera  20 . 
         [0043]    Some vehicles such as for example certain school buses or tractor-trailers, an example of which is shown at  42  in  FIG. 7   a , have a high-rising rear end  44  (ie. a rear end that is relatively elevated off the road surface). If the host vehicle follows a target vehicle  42  with a high-rising rear end  44 , the long-range sensor  22 , which may operate using a narrow vertical opening angle (shown at  46 ) of between 2 and 5 degrees may, depending on the mounting height of the long-range sensor  22  in the host vehicle  10  not detect the rear end  44  of the target vehicle  42 . Instead the long-range sensor  22  may have an unobstructed view onto the rear axle shown at  48 , which may be several meters in front of the rear end  44 . The ultrasonic sensors  24  on the other hand may utilize a very wide vertical opening angle, shown at  50 , that can detect objects up to about 1.8 m height at about 2.5 m distance and could therefore detect the rear end  44  of the preceding vehicle  42  when the host vehicle  10  is sufficiently close to the preceding vehicle  42  (as shown in  FIG. 7   b ). For use in the follow-to-stop adaptive cruise control system  12 , the distance information reported to the central fusion processing module  14  by the long-range sensor  22  and by the short-range sensors  24  may differ because the long-range sensor  22  may sense the rear axle  48 , while the short-range sensors sense the actual rear end  44 . In this case the host vehicle  10  may be brought to a complete stop based on object information from the camera  20  and the short-range sensors  24  while ignoring the information from the long-range sensor  22 . 
         [0044]      FIG. 6  shows a graph illustrating an exemplary method of operating the ultrasonic sensing system  25 . When the host vehicle  10  ( FIG. 1 ) is moving at a speed that is higher than a first threshold speed V 1  ( FIG. 6 ), which may be referred to as a slow speed, the ultrasonic sensors  24  ( FIG. 1 ) are off, as they would not provide useful information to the main controller  14 . When the host vehicle  10  ( FIG. 1 ) is moving at a speed that is between the slow speed V 1  and a lower, second threshold speed V 2  ( FIG. 6 ) (which may be referred to as a very-slow speed), the controller  14  ( FIG. 2   a ) operates the ultrasonic sensors  24  in a short range operating mode wherein, two or more of the plurality of ultrasonic sensors  24  ( FIG. 1 ) may operate together in ‘synchronous mode’, emitting long pulses and listening in parallel for reflections. Referring to  FIG. 1 , in embodiments wherein four sensors  24  are provided across the width of the host vehicle  10 , the middle two sensors  24   b  and  24   c  (ie. the sensors  24   b  and  24   c  that are generally proximate the longitudinal centerline shown at  126  of the host vehicle  10 ) may be used for the operation of the sensor system  25  in the short range operating mode. When the host vehicle  10  ( FIG. 1 ) is moving at a speed that is between the very-slow speed V 2  and a third threshold speed V 3  ( FIG. 6 ) which may be referred to as a super-slow speed, the controller  14  may operate the ultrasonic sensors in a very-short range operating mode, wherein the plurality of ultrasonic sensors  24  ( FIG. 1 ) operate sequentially in A-A mode each sensor  24  in sequence emitting a long pulse and listening for reflections of the emitted long pulse. For example, sensor  24   a  may first emit a long pulse and listen for reflections. Then sensor  24   b  emits a long pulse and listens for reflections, and so on. When operating in this way, at least some positional information is provided to the main controller  14 , based on which sensor  24  senses the closest object. Referring to  FIG. 1 , in embodiments wherein four sensors  24  are provided across the width of the host vehicle  10 , all or some of the sensors  24  may be used for the operation of the sensor system  25  in the very-short range operating mode. When the host vehicle  10  ( FIG. 1 ) is moving at a speed that is lower than the super-slow threshold speed V 3  ( FIG. 6 ), the ultrasonic sensors  24  may be operated in a super-short range operating mode wherein the sensors  24  are operated sequentially as follows: Each sensor  24  in sequence is operated in a cycle  56  that includes a short pulse stage  58  and a long pulse stage  60 . In the short pulse stage  58 , the sensor  24  emits a short pulse and the other sensors  24  listen for a reflection (A-B mode). In the long pulse stage  60  the sensor  24  sends a long pulse and listens for the reflection (A-A mode). Thus, the first sensor  24   a  goes through the cycle  56  of operation; then the second sensor  24   b  goes through the cycle  56  of operation; then the third sensor  24   c , and then the fourth sensor  24   d . In each case where the sensors  24  are operated in sequence, the sequence of operation may be a repeating sequence of  24   a ,  24   b ,  24   c  and  24   d , or it may be some other sequence. 
         [0045]    While the present invention has been described with reference to exemplary embodiments, it will be readily apparent to those skilled in the art that the invention is not limited to the disclosed or illustrated embodiments but, on the contrary, is intended to cover numerous other modifications, substitutions, variations and broad equivalent arrangements that are included within the spirit and scope of the following claims.