Abstract:
An adaptive cruise control system includes a forward-looking sensor generating a range signal corresponding to a distance between the host vehicle and a target vehicle. The forward-looking sensor also generates a range rate signal corresponding to a rate that the distance between the host vehicle and the target vehicle is changing. A controller is electrically coupled to the forward-looking sensor. The controller maintains a preset headway distance between the host vehicle and the target vehicle by adjusting the host vehicle velocity in response to the range signal and the range rate signal. The host vehicle may come to a full stop when the target vehicle is acquired below a predetermined velocity. If the target vehicle is acquired above the predetermined velocity, then a warning is given when braking is required.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to vehicle adaptive cruise control systems, and more particularly to a method and apparatus for adjusting vehicle speed and maintaining a headway distance in response to a target. 
     Adaptive Cruise Control (ACC) has reached a level of technical and business readiness such that it is beginning to appear in the consumer market as a comfort and convenience system. Consumer technical enthusiasm for ACC has increased because of their interest in intelligent vehicles and systems such as collision warning and collision avoidance. ACC performs as an enhancement to traditional cruise control by automatically adjusting a set speed, which is set by the vehicle operator, to allow a vehicle to adapt to moving traffic. 
     Under normal driving conditions the ACC system is engaged with a set speed equal to a maximum autonomous speed that is desired by the operator and the ACC system operates in a conventional cruise control mode. When the vehicle approaches traffic, the ACC system automatically adjusts the set speed to follow the traffic at a desired headway distance. When the traffic clears, the ACC system slowly resumes the speed of the vehicle to the set speed. When the ACC vehicle performs a lane change, and the actual distance to a new target is less than the set headway distance, the ACC vehicle will remain in follow mode. When the vehicle approaches slow traffic, whereby the ACC system determines to reduce speed of the vehicle below a minimum speed for ACC operation, the ACC system is automatically disengaged and the operator manually follows slower vehicles in the slow traffic. When the slow traffic is no longer in front of the vehicle the operator must manually accelerate the vehicle to a velocity above the minimum speed for ACC operation, approximately 40 KPH, before the ACC system is able to resume acceleration to the set speed by depression of a resume button. 
     During slower stop and go traffic the operator frequently adjusts the speed of the vehicle by applying the brakes or depressing the accelerator. The continuous adjusting of the vehicle speed can become frustrating for the operator over extended periods of time. 
     Traditional ACC systems were designed to only react to moving targets presented by normal traffic under extended cruise control operation and when the vehicle is traveling at velocities above 40 KPH. Therefore, by operating only when certain conditions exist, the ACC system is compromising the goals of a collision warning or avoidance system. 
     It would therefore be desirable to develop an ACC system that operates at vehicle speeds below 40 KPH. It would also be desirable for the ACC system to correctly classify targets when traveling at the slower speeds. The ability to operate and classify targets at slower speeds may increase the success of ACC systems in the consumer market and also increase the collision warning capabilities of a vehicle. 
     SUMMARY OF INVENTION 
     The foregoing and other advantages are provided by a method and apparatus for adjusting vehicle speed and maintaining a headway distance in response to a target. An ACC system includes a forward-looking sensor generating a range signal corresponding to a distance between the host vehicle and a target vehicle. The forward-looking sensor also generates a range rate signal corresponding to a rate that the distance between the host vehicle and the target vehicle is changing. A controller is electrically coupled to the forward-looking sensor. The controller maintains a preset headway distance between the host vehicle and the target vehicle by adjusting the host vehicle velocity in response to the range signal and the range rate signal. The host vehicle may come to a full stop when the target vehicle is acquired below a predetermined velocity. If the target vehicle is acquired above the predetermined velocity, then a warning is given when braking is required. 
     The present invention itself, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which: 
     FIG. 1 is a block diagram view of a stop and go adaptive cruise control (ACC) system in accordance with an embodiment of the present invention; 
     FIG. 2 is a pictorial view of a host vehicle using the stop and go ACC system in a congested traffic situation in accordance with an embodiment of the present invention; 
     FIG. 3 is a pictorial view of a host vehicle using the stop and go ACC system while adjusting lanes to avoid a stopped vehicle in accordance with an embodiment of the present invention; 
     FIG. 4 is a pictorial view of a host vehicle using the stop and go ACC system, while following a target vehicle making a right turn from a complete stop, in accordance with an embodiment of the present invention; 
     FIG. 5 is a pictorial view of a host vehicle using the stop and go ACC system, while following a target vehicle making a left turn from a complete stop, in accordance with an embodiment of the present invention; 
     FIG. 6 is a pictorial view of a host vehicle using the stop and go ACC system and encountering merging traffic from an entrance ramp, in accordance with an embodiment of the present invention; 
     FIG. 7 is a pictorial view of a host vehicle using the stop and go ACC system, while changing lanes in stop and go traffic, in accordance with an embodiment of the present invention; 
     FIG. 8 is a pictorial view of a host vehicle using the stop and go ACC system and encountering a “cut-in” vehicle, in accordance with an embodiment of the present invention; 
     FIG. 9 is a pictorial view of a host vehicle using the stop and go ACC system and encountering an oncoming vehicle, in accordance with an embodiment of the present invention; 
     FIG. 10 is a pictorial view of a host vehicle using the stop and go ACC system and encountering an object, in accordance with an embodiment of the present invention; 
     FIG. 11 is flow chart illustrating a method of maintaining a preset headway distance between the host vehicle and a target in accordance with an embodiment of the present invention; and 
     FIG. 12 is a sample state transition diagram illustrating the operation of the stop and go ACC system in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In each of the following figures, the same reference numerals are used to refer to the same components. While the present invention is described with respect to a method and apparatus for adjusting vehicle speed and maintaining a headway distance in response to a target, the present invention may be adapted to be used in various systems including: cruise control systems, forward collision warning systems, collision avoidance systems, vehicle systems, or other systems that may require adaptive speed control. 
     In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting. 
     Referring now to FIG. 1, a block diagrammatic view of a stop and go adaptive cruise control (ACC) system  10  in accordance with an embodiment of the present invention is shown. The system  10  is located within a host vehicle  12  that has a braking system  14  and an engine management system  16 . System  10  includes a forward-looking sensor  18  for sensing a target in the path of the host vehicle  12 . The forward-looking sensor  18  generates a range signal corresponding to a distance between the host vehicle  12  and a target and a range rate signal corresponding to a rate said distance between the host vehicle  12  and said target is changing. A stop and go controller  20  receives the rate signal and the range rate signal and determines whether to signal the braking system  14  or to signal the engine management system  16  as to maintain a preset distance between the host vehicle  12  and the target. The controller  20  maintains the preset distance for host vehicle velocities from zero to 50 KPH. The system  10  may also include other components such as a driver interface  22 , a global positioning system  24 , a vehicles dynamics system  26 , various indicators  28 , and other components as will become more evident from the following description. 
     The braking system  14  may include any vehicle system known in the art that is capable of reducing the velocity of the host vehicle  12 . Although, the braking system  14  of the present invention comprises two devices  30  for reducing the velocity of the host vehicle  12 , other similar systems may be used. For example a transmission controller (not shown) that is capable of downshifting a transmission of the host vehicle  12  may be used to reduce the host vehicle velocity. The braking system  14  of the present invention includes a brake booster controller  32  and an electric park brake assist  34 . The brake booster controller  32  is equivalent to a vehicle operator applying the brakes. The electric park brake assist  34  is used when additional braking power is requested by the controller  20 . The electric park brake assist may be used as a fail-safe mechanism when a failure occurs within the booster (not shown) of the braking system  14 . 
     The engine management system  16  may include any host vehicle components that adjust the acceleration of the vehicle. These components may include a vehicle accelerator  36  such as in the present invention, a fuel and air intake control system, an engine timing controller, or other vehicle component or system known in the art that may be used to adjust the velocity of the host vehicle  12 . 
     Forward-looking sensor  18  may be of various type known in the art including a radar sensor, a lidar sensor, a combination of a radar sensor and a camera system or other forward-looking sensor. Although, the forward-looking sensor  18  of the present invention is a single frontal mounted sensor, multiple forward-looking sensors mounted at various locations on the host vehicle  12  may be used. The forward-looking sensors may be front mounted, side mounted, or even rear mounted. The purpose of the forward-looking sensor  18  is to sense position and velocity of a target located in a future path of the host vehicle  12  and relative to the host vehicle  12 . The target may be any of the following: a vehicle, a stopped object, a moving object, a bridge, construction equipment, a sign, an animate or inanimate object, or other object. The forward-looking sensor  18  may also gather other information including target angel relative to the host vehicle  12  and yaw rate of the target relative to the host vehicle  12 . The additional information allows the controller  20  to more accurately determine the threat of the target as to the host vehicle  12  and the appropriate actions to perform. 
     Controller  20  may be a microprocessor based controller such as a computer having a central processing unit, memory (RAM and/or ROM), and associated input and output buses. Controller  20  may be a portion of a main control unit, such as a main vehicle controller, or may be a stand-alone controller. The controller  20  of the present invention contains logic for maintaining a preset distance between a target and the host vehicle  12  while operating at a low host vehicle velocity and a midrange host vehicle velocity. The low host vehicle velocity includes approximately any velocity below 40 KPH, including an at rest velocity of 0 KPH. The midrange host vehicle velocity includes approximately velocities greater than or equal to 40 KPH and less than 50 KPH. The controller  20  allows an operator to activate the system  10  at any velocity below 50 KPH. The controller  20 , while activated, maintains a preset distance between the host vehicle  12  and the target. The preset distance is maintained when the host vehicle velocity is from 0 KPH up to 50 KPH, from 50 KPH down to 0 KPH, and any other scenario. The controller  20  automatically disengages for host vehicle velocities above 50 KPH at which point traditional ACC systems may take over. The preset distance may be set by an operator or may be set during production of the system  10 . 
     The controller  20  may have an initialization hold time, during which the controller  20  holds the host vehicle  12  stationary until an operator reactivates system  10  to resume operation by pressing on the accelerator  36 , pressing on a brake pedal (not shown) within the vehicle  12 , switching the reengage switch  44 , or by another reactivation method known in the art. The controller  20  may also hold the host vehicle  12  stationary for a predetermined amount of time after the system  10  reduces the velocity of the host vehicle  12  to a complete stop. The controller  20  reactivates the system  10  after the predetermined time has lapsed or waits until the operator reinitializes or deactivates the system  10 . 
     An embodiment of the present invention includes the driver interface  22 , as represented by dashed arrows  38 . The driver interface  22  may have several different switches  39  including a “ON”switch  40 , a “Follow” switch  42 , a “Reengage” switch  44 , or a “Headway” adjustment switch  46 . Switches  39  allow the operator to activate, deactivate, resume operation, and adjust the distance between the host vehicle  12  and a target. The functions that switches  39  perform may be included and automatically implemented through logic within the controller  20 . The headway adjustment switch  46  may have several settings for example it may have a short, a medium, or a long setting representing different desired set distances that may be maintained between the host vehicle  12  and a target. The switches  39  may be of various type and style as known in the art. 
     The global positioning system  24  may be incorporated in conjunction with the forward-looking sensor  18  as to detect environment situations, such as an exit ramp, a round-a-bout, or other environmental situations. This is represented by dashed arrow  50 . 
     The vehicle dynamics system  26  is provided in another embodiment of the present invention, as represented by the dashed arrow  52 . The vehicle dynamics system  26  uses vehicle sensors (not shown) to measure inertial information of the host vehicle  12 . When instability of the host vehicle  12  occurs, the vehicle dynamics system  26  may deactivate the system  10 . By deactivating system  10 , a false reaction by the controller  10  may be prevented. 
     The system  10  may also include the various indicators  28 . Some contemplated indicators are as follows. An indicator may be used to inform an operator that the system  10  is holding the host vehicle  12  stationary, that acceleration of the host vehicle  12  is being controlled, or that the controller  20  is stopping the host vehicle  12 . An audible or visual indicator may be provided as to warn the operator that the braking performed by the controller  20  is insufficient to slow down the host vehicle  12  and that the operator should intervene. 
     Referring now to FIGS. 2-10, various possible situations are illustrated that may occur during use of the system  10 . Each of these situations may have different logic associated with and stored in the controller  20 , so as to perform differently as needed. 
     In FIG. 2, the host vehicle  12  is using the system  10  in a congested traffic situation. The system  10  maintains a preset distance between the host vehicle  12  and a target vehicle  60 . 
     In FIG. 3, the host vehicle  12  is using the system  10  while changing lanes to avoid a stopped vehicle  62 . The system  10  detects a vehicle  64  in the future path of the host vehicle  12  and as in FIG. 2 maintains a preset distance between the host vehicle  12  and the detected vehicle  64 . 
     In FIG. 4, the host vehicle  12  is using the system  10  while following a target vehicle  66  making a right turn from a complete stop. In this situation the system  10  may perform several different actions. The system  10  may hold the host vehicle  12  stationary until intervention by an operator, the system  10  may detect an oncoming vehicle  68  and also hold the host vehicle  12  stationary until the oncoming vehicle  68  passes, or the system  10  may determine that the oncoming vehicle  68  is at a safe distance and allow the host vehicle  12  to continue following the target vehicle  66 . Actions are determined in response to detected vehicle positioning and traveling velocities relative to the host vehicle  12 . 
     In FIG. 5, the host vehicle  12  is using the system  10  while following a target vehicle  70  making a left turn from a complete stop. As with the situation in FIG. 4 the system  10  may perform several actions. Also as with FIG. 4 the system  10  will determine vehicle positioning using various detection devices described above as to determine what action to perform. Note when the system  10  encounters a situation that it is not familiar with or is unable to determine what action to perform it may indicate this to the operator and wait for operator intervention. 
     In FIG. 6, the host vehicle  12  is using the system  10  and encountering merging traffic  80  from an entrance ramp  82 . Rather than continuing to follow a target vehicle  86  at a preset distance the system  10  may reduce the velocity of the host vehicle  12  as to now follow a new target vehicle  88 . Of course, for any of the described situation in this application the controller  20  may be programmed to wait for operator intervention before continuing to act. 
     In FIG. 7, the host vehicle  12  is using the system  10  while changing lanes in stop and go traffic  90 . As in other described situations the system  10  may determine to follow a new target vehicle  92  instead of following the original target vehicle  94 . 
     In FIG. 8, the host vehicle  12  is using the system  10  and encountering a “cut-in” vehicle  96 . Similar to that of FIG. 6 the system  10  may determine to reduce the velocity of the host vehicle  12  as to let the cut-in vehicle  96  in front of the host vehicle  12  and then resume following the cut-in vehicle  96  at a preset distance. 
     In FIG. 9, the host vehicle  12  is using the system  10  and encountering an oncoming vehicle  100 . In this situation the system  10  may indicate to the operator to intervene and may also reduce the velocity of the host vehicle  12  to zero KPH as to prevent a collision with the oncoming vehicle  100 . 
     In FIG. 10, the host vehicle  12  is using the system  10  and encountering a pedestrian  102  or some other object other than another vehicle. The system  10  may determine to reduce the velocity of the host vehicle  12  to 0 KPH as to prevent colliding with the object  102 . 
     Of course, the above-described situations are not all encompassing and the controller  20  may be programmed to act for other situations. 
     Referring now to FIG. 11, a flow chart illustrating a method of maintaining a preset headway distance between the host vehicle  12  and a target, while traveling at a low or midrange host vehicle velocity of less than 50 KPH, in accordance with an embodiment of the present invention is shown. 
     In step  110 , the system  10  is initialized as described above. The system  10  is activated and determines the relative positioning and relative velocities of objects surrounding the host vehicle  12 . In doing so, determining the appropriate action to perform. 
     In step  112 , the system  10  senses a target using a detection device such as the forward-looking sensor  18 . A range signal and a range rate signal is generated corresponding to the distance between the host vehicle  10  and the target and the rate of change of this distance, respectively. 
     In step  114 , the system  10  maintains a preset distance between the host vehicle  12  and the target. This may occur in a couple different situations either the host vehicle  12  is stationary and determines to begin accelerating and following the target or the host vehicle  12  is already travel at a certain velocity and adjusts the host vehicle velocity as to maintain the set distance. 
     Referring now to FIG. 12, a sample state transition diagram illustrating the operation of the system  10  according to an embodiment of the present invention is shown. 
     In state Stop and Go Off, the system  10  is deactivated. The system  10  may be sensing objects in a close proximity to the host vehicle  12  as to warn the operator. 
     In state Stop and Go Standby, the system  10  is in a standby mode. Upon receiving a power on command the system  10  initializes as described above and sits idle until further commanded. 
     In state Stop and Go Active, the system  10  is activated as to follow and maintain a preset distance between the host vehicle  12  and a target. The system  10  may act as a traditional cruise control system, illustrated by a Cruise state and corresponding sub states, as known in the art or may perform otherwise depending upon the detection of objects in the close proximity of the host vehicle. The system  10  may resort back to the stop and go off state or the stop and go standby state for various reasons as described above. 
     In state Follow, a target has been detected and the system maintains the preset distance. The preset distance is maintained by four different states, a Stop state, a Go state, a Follow Resume state, and an Opening Range state. The controller  20  monitors the distance between the host vehicle and the target vehicle as well as the relative range rate to determine an appropriate resolved host vehicle velocity. The resolved host vehicle velocity represents a safe host vehicle traveling velocity to maintain the preset distance. 
     During the Stop state the host vehicle velocity is greater then the target velocity or the distance between them is less than the preset distance. The system  10  reduces the velocity of the host vehicle  12  by signaling the braking system  14 . 
     During the Go state, the difference between the host vehicle velocity and the resolved host vehicle velocity is less than a predetermined value, or the range rate is less than or equal to a predetermined value and the difference in velocity is greater than or equal to zero. The system  10  is signaling the engine management system  16  to not signal the braking system  14 . Typically in this state, the host vehicle velocity is approximately equal to the target velocity. 
     During the Follow Resume state, the difference between the host vehicle velocity and the host vehicle&#39;s target velocity is greater than or equal to a predetermined value the system  10  resumes following the target by accelerating or decelerating the vehicle. When the difference between the host vehicle velocity and the host vehicle target velocity is less than the predetermined value than the system  10  returns to the green state. 
     During the Opening Range state, the range rate between the host vehicle  12  and the target is greater than a predetermined value and the velocity difference between the host vehicle  12  and the target is less than zero. The system  10  reduces the amount that it is accelerating the host vehicle  12  as to prevent a collision. When the range rate is less than the predetermined value the system  10  returns to the green state. 
     The Stop and Go Active state also includes a Follow Override state. The Follow Override state is performed when either the operator intervenes, a justified malfunction occurs in a host vehicle system, the braking system is insufficiently reducing the velocity of the host vehicle  12 , or for other various reasons that may be envisioned by one skilled in the art. 
     A Recover Brake state is also provided when a problem exists in the braking system  14 . The system  10  indicates to the operator that the system  10  is not able to decelerate the host vehicle  12  because of insufficient braking in the braking system  14 . The system  10  may apply an emergency brake, such as the electric park brake assist  34 , or decelerate the host vehicle  12  using other methods as described above. 
     The present invention provides an ACC system that is operable for all host vehicle velocities less than 50 KPH. The present invention also reduces the amount of tedious actions that an operator has to perform in stop and go traffic. The aforementioned reviews how the present invention increases collision-warning capabilities of a host vehicle. 
     The above-described apparatus, to one skilled in the art, is capable of being adapted for various purposes and is not limited to the following systems: cruise control systems, forward collision warning systems, collision avoidance systems, vehicle systems, or other systems that may require adaptive speed control. The above-described invention may also be varied without deviating from the spirit and scope of the invention as contemplated by the following claims: