Patent Publication Number: US-11390207-B2

Title: Headlight control apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a headlight control apparatus for automatically controlling an irradiation (emitting) direction of a headlight on the basis of a pitch angle of a vehicle. 
     BACKGROUND 
     A conventionally known headlight control apparatus (hereinafter also referred to as the “conventional apparatus”) of this kind is equipped with a vehicle height sensor for detecting a change amount in a height of a rear. wheel axle (namely, a relative displacement amount of a spring upper member of the vehicle with respect to the rotation axis of the rear wheel). In addition, the conventional apparatus obtains (estimates) the pitch angle on the basis of the detected change amount in the height (see, for example, Japanese Patent Application Laid-Open (kokai) No. H10-226271). 
     According to the conventional apparatus, it is possible to obtain the pitch angle without disposing the vehicle height sensors for both a front wheel and the rear wheel. 
     SUMMARY 
     However, even if the change amount in the height is the same value (namely, the change amount in the height does not change), there may be a case where the pitch angle differs. For example, even if the change amount in the height is the same value, the vehicle leans backward more in a case where luggage is loaded at a position (for example, a rear trunk of the vehicle) behind the rear wheel axle as compared with a case where luggage is not loaded. In other words, even if the change amount in the height is the same value, the pitch angle may vary depending on a position of the center of gravity of a load (hereinafter also referred to as a “vehicle load”) of the vehicle including a driver, an occupant (passenger) and luggage. Namely, the position of the center of gravity of the vehicle load may affect/influence the pitch angle estimated/extrapolated by the conventional apparatus, and thus, there may be a case where a difference between that estimated pitch angle and an actual value of the pitch angle is relatively large. 
     Incidentally, a vehicle equipped with a camera apparatus for obtaining a “travelling direction image” by capturing (photographing) an image of a region in a travelling direction of the vehicle is known. This kind of the vehicle, for example, provides a driving support function for automatically control a travelling speed and/or a steering angle (turning angle) of that vehicle according to a type and a position of an object contained in (furthermore, extracted from) the travelling direction image. 
     In view of the forgoing, one object of the present disclosure is to disclose a headlight control apparatus that can more accurately obtain (extrapolate) the pitch angle of a vehicle by utilizing a camera apparatus installed in the vehicle. 
     The headlight control apparatus for achieving the above-described object (hereinafter also referred to as “the apparatus of the present disclosure”) comprises an actuator, a controller, a vehicle height sensor and a camera apparatus. The controller may be implemented by at least one programmed processor whose operation is determined by a predetermined program, gate arrays and the like. 
     The actuator adjusts (controls) an irradiation angle (θb) of a headlight (low beam unit  31 ) of a vehicle ( 10 ). 
     The controller (headlight control ECU  20 , image processing section  52 ) obtains a target irradiation angle (θbtgt) on the basis of a pitch angle (θp) of the vehicle; and controls the actuator such that the irradiation angle coincides with the target irradiation angle. 
     The vehicle height sensor ( 61 ) detects a relative displacement amount of a spring upper member of the vehicle with respect to a rotation axis of either a front wheel or a rear wheel of the vehicle as a contraction length (Ca). 
     The camera apparatus ( 50 ) obtains a “travelling direction image” by photographing a region in a travelling direction of the vehicle. 
     Furthermore, the controller executes an “infinity point obtainment processing” for obtaining an infinity point correlation value (infinity point position Yi, current pitch angle θn) having a correlation with an infinity point position (Yi) which is a position of an infinity point (for example, a point Pf in  FIG. 4 ) contained in the travelling direction image in a vertical direction of the travelling direction image. 
     In addition, the controller determines whether a predetermined “standard value obtainment condition” is satisfied. 
     The controller execute a “standard value obtainment processing” for obtaining a standard pitch angle (θstd) by applying the detected contraction length to a predetermined relationship (relationship represented by a straight line Le in  FIG. 5 ) between the contraction length and the pitch angle and for obtaining the infinity point correlation value at the present time as a standard infinity point correlation value (standard infinity point position Ystd, reference pitch angle θref), when it is determined that the standard value obtainment condition is satisfied (step  725  and step  730  in  FIG. 7  and  FIG. 10 , and step  925  and step  730  in  FIG. 9  and  FIG. 11 ). 
     Meanwhile, the controller executes a “pitch angle estimation processing” for obtaining the pitch angle on the basis of the standard pitch angle, the standard infinity point correlation value, and the infinity point correlation value at the present time, when it is determined that the standard value obtainment condition is not satisfied (step  740  in  FIG. 7  and  FIG. 10 , and step  942  in  FIG. 9  and  FIG. 11 ). 
     For example, if the infinity point position at a point in time when the pitch angle is 0° (namely, the vehicle is neither leaning forward nor backward) has been obtained as an image base point, it is possible to obtain the pitch angle at the present (current) time on the basis of the infinity point position at the present time and the image base point. The image base point can be obtained, for example, on the basis of an image captured by the camera apparatus, the image containing an image of a target object that is placed/positioned in front of the camera apparatus in a factory where the vehicle is manufactured, and on the basis of a positional relationship between the camera apparatus and the target object. 
     However, it may not be easy to accurately place/position the target object at a predetermined position in front of the camera apparatus (namely, in front of the vehicle) in many cases, and thus, there will be a higher possibility that an error of the obtained image base point is relatively large. Meanwhile, the infinity point position in the travelling direction image captured when the vehicle is travelling can be obtained by a well-known method with comparative accuracy. Namely, it is possible to relatively accurately obtain the infinity point correlation value on the basis of the travelling direction image. Therefore, the pitch angle can be accurately obtained on the basis of the travelling direction image even when the vehicle height sensors for both the front wheel and the rear wheel are not provided. 
     In one aspect (first aspect) of the apparatus of the present disclosure, the controller is configured to determine that the standard value obtainment condition is satisfied when the detected contraction length falls within a predetermined “standard range” (range from a first contraction length C 1  to a second contraction length C 2 ). 
     The standard range employed by the apparatus of the present disclosure is, for example, a range of the contraction length in which the pitch angle can be obtained/extrapolated with comparative accuracy based on the contraction length. In addition, the standard pitch angle and the standard infinity point correlation value are obtained when the contraction length falls within the standard range. Accordingly, it is possible to accurately obtain the pitch angle on the basis of the standard pitch angle and the standard infinity point correlation value, even when the contraction length is not included in the standard range. 
     Therefore, according to the first aspect, it is possible to accurately obtain the pitch angle (i.e., extrapolate the pitch angle used for determining the target irradiation angle) by utilizing the camera apparatus installed in the vehicle. 
     In the first aspect, the controller may be configured to employ, as the standard range, a range from a minimum value to a maximum value of the contraction length obtained while a load of the vehicle is a driver only (see  FIG. 5 ). 
     If the vehicle load is the driver only, the position of the center of gravity of the vehicle load substantially remains unchanged irrespective of the driver&#39;s weight (namely, a body weight). Accordingly, if the vehicle load is the driver only, the contraction length detected by the vehicle height sensor is approximately the same value. Therefore, according to the present aspect, the standard pitch angle and the standard infinity point correlation value are obtained when a difference between the pitch angle estimated on the basis of the contraction length and the actual value of the pitch angle is relatively small, and thus, the pitch angle can be accurately obtained based on the relatively accurate standard pitch angle and the relatively accurate standard infinity point correlation value. 
     In still another aspect (second aspect) of the apparatus of the present disclosure, the controller is configured to determine that the standard value obtainment condition is satisfied when the detected contraction length is smaller than a “value obtained by subtracting a difference threshold (a) from a standard contraction length (Cstd).” In addition, the controller is configured to update the standard contraction length such that the standard contraction length is set to a value equal to the detected contraction length of when it is determined that the standard value obtainment condition is satisfied. 
     In a period from a time point when the vehicle starts travelling for the first time (a first travelling starting time point, namely, a time point when the vehicle starts a first travelling after the vehicle is manufactured) to a time point when the standard value obtainment condition is satisfied for the first time, the standard pitch angle and the standard infinity point correlation value cannot be obtained, and thus, the pitch angle cannot be obtained/extrapolated based on the standard pitch angle and the standard infinity point correlation value. Accordingly, it is preferable that the period from the first travelling starting time point to the time point when the standard value obtainment condition is satisfied for the first time be short. 
     According to the second aspect, the standard value obtainment condition is satisfied when the contraction length is smaller than a value obtained by subtracting the difference threshold from an initial value of the contraction length (namely, a value of the contraction length before a time point when standard value obtainment condition is satisfied for the first time which is set when the vehicle was manufactured). Therefore, according to the present aspect, it is possible to shorten the period from the first travelling starting time point to the time point when the standard value obtainment condition is satisfied for the first time. 
     In the second aspect, the controller may be configured to set the standard contraction length to a value (contraction length initial value Ci) larger than a value obtained by adding the difference threshold to an upper limit (maximum contraction length Cmax) of a range of the detected contraction length in a case where the standard pitch angle has not been obtained yet. 
     According to this aspect, it is certainly possible to shorten the period from the first travelling starting time point to the time point when the standard value obtainment condition is satisfied for the first time. 
     In still another aspect (third aspect) of the apparatus of the present disclosure, the controller is configured to obtain the pitch angle on the basis of a relationship that a first difference value is proportional to a second difference value (see an expression (13)), the first difference value being a difference between the tangent of the pitch angle at the present time and the tangent of the standard pitch angle (tan(θp)−tan(θstd)), and the second difference value being a difference between the standard infinity point correlation value and the infinity point correlation value at the present time (Ystd−Yi). 
     The infinity point correlation value is, for example, a position of a pixel (pixel position) in the vertical direction (namely, up and down direction) corresponding to the infinity point in “the travelling direction image which is a set of pixels.” This pixel position changes as the pitch angle (more specifically, the tangent of the pitch angle) changes. Therefore, according to the third aspect, the pitch angle can be accurately obtained by a well-known calculation method using the trigonometric function. 
     In still another aspect (fourth aspect) of the apparatus of the present disclosure, the controller is configured to obtain the pitch angle on the basis of a relationship that a third difference value is proportional to a fourth difference value (see an expression (4)), the third difference value being a difference between the pitch angle at the present time and the standard pitch angle (θp−θstd), and the fourth difference value being a difference between the standard infinity point correlation value and the infinity point correlation value at the present time (Ystd−Yi). 
     The pitch angle varies as the weight and the position of the center of gravity of the vehicle load changes. However, generally, a magnitude of the pitch angle does not become excessive (the magnitude of the pitch angle is relatively small). Accordingly, an error (obtainment error) of the pitch angle is relatively small, even if that pitch angle is obtained based on the assumption that the third difference value is proportional to the fourth difference value. A proportionality constant in this case is, for example, a value obtained by dividing a field angle (θa) which is an angle of view of the camera apparatus in the vertical direction by a vertical pixel number (Yd) which is a number of pixels constituting the travelling direction image in the vertical direction. Therefore, according to the fourth aspect, it is possible to obtain the pitch angle with comparative accuracy by a simple process. 
     In still another aspect (fifth aspect) of the apparatus of the present disclosure, the controller is configured to obtain, as the infinity point correlation value (current pitch angle θn), a value proportional to a difference (Yo−Yi) between a specific infinity point position (image base point Yo) and the infinity point position at the present time, the specific infinity point position being the infinity point position obtained when the pitch angle was equal to a predetermined specific angle (0°). In addition, the controller is configured to obtain, as the pitch angle, a value obtained by adding the standard pitch angle to a difference (displacement pitch angle θfoe) between the infinity point correlation value and the standard infinity point correlation value (reference pitch angle θref) (see an expression (9)). 
     For example, the specific angle is 0°, which corresponds to a state where the vehicle is neither leaning forward nor backward. The specific infinity point position is, for example, obtained on the basis of the travelling direction image obtained (captured) while the vehicle stops (when the vehicle is not travelling). As described above, in many cases, it is not easy to accurately obtain the position of the infinity point in the travelling direction image which is obtained while the vehicle stops. 
     Meanwhile, in the fifth aspect, an error in the standard infinity point correlation value due to the inaccurate specific infinity point position and an error in the infinity point correlation value at the present time due to the inaccurate specific infinity point position are eliminated, because the errors are in common between the standard infinity point correlation value and the infinity point correlation value at the present time. Therefore, according to the fifth aspect, the pitch angle can be obtained accurately even if it is not easy to accurately obtain the specific infinity point position. 
     Notably, in the above description, in order to facilitate understanding of the present disclosure, the constituent elements of the disclosure corresponding to those of an embodiment of the disclosure which will be described later are accompanied by parenthesized names and/or symbols which are used in the embodiment; however, the constituent elements of the disclosure are not limited to those in the embodiment defined by the names and/or the symbols. Other objects, other features, and attendant advantages of the present disclosure will be readily appreciated from the following description of the embodiment of the disclosure which is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a vehicle (present vehicle) on which a headlight control apparatus according to a first embodiment of the present disclosure (first control apparatus) is mounted; 
         FIG. 2  is a block diagram of the first control apparatus; 
         FIG. 3  is a diagram showing a structure of a low beam unit included in the present vehicle; 
         FIG. 4  is an example of a front image photographed by a camera apparatus included in the present vehicle; 
         FIG. 5  is a graph showing a relationship between a detected value (contraction length) of a vehicle height sensor included in the present vehicle and a pitch angle of the present vehicle; 
         FIG. 6A  is a side view of the present vehicle when the pitch angle is a standard pitch angle; 
         FIG. 6B  is a side view of the present vehicle when the pitch angle is an angle different from the standard pitch angle; 
         FIG. 7  is a flowchart representing an auto-leveling processing routine executed by the first control apparatus; 
         FIG. 8  is a diagram for explaining a process in which a first modification of the first embodiment of the present disclosure (first modification apparatus) obtains the pitch angle; 
         FIG. 9  is a flowchart representing the auto-leveling processing routine executed by the first modification apparatus; 
         FIG. 10  is a flowchart representing the auto-leveling processing routine executed by the headlight control apparatus according to a second embodiment of the present disclosure; 
         FIG. 11  is a flowchart representing the auto-leveling processing routine executed by the headlight control apparatus according to a modification of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A headlight control apparatus according to a first embodiment of the present disclosure (hereinafter also referred to as the “first control apparatus”) will now be described with reference to the drawings. The first control apparatus is applied to a vehicle  10  shown in  FIG. 1 . As understood from  FIG. 2  illustrating a block diagram of the first control apparatus, the first control apparatus includes a headlight control ECU  20  which is an electronic control unit (ECU). Hereinafter, the headlight control ECU  20  is also referred to as the ECU  20  for simplification. 
     The ECU  20  includes a micro-computer which is equipped with a CPU  25 , a ROM  26 , a RAM  27  and a non-volatile memory  28  as major components. The CPU  25  performs data reading, numerical computation, computation result output, and so on, by repeatedly executing predetermined programs (routines). The ROM  26  stores the programs executed by the CPU  25 , lookup tables (maps) read by the CPU  25  during execution of the programs, and so on. The RAM  27  temporarily stores data read by the CPU  25 . The non-volatile memory  28  is formed by a rewritable flash memory and stores data (for example, a standard infinity point position Ystd and a standard pitch angle θstd described later) specific to the vehicle  10  itself. 
     The ECU  20  is connected to a headlight  30 , a camera apparatus  50 , a vehicle height sensor  61 , and a dimmer switch  62 . 
     The headlight  30  includes a low beam unit  31 , and a high beam unit  32 . The low beam unit  31  includes a left low beam unit  31   a , and a right low beam unit  31   b.    
     An irradiation range in a vertical direction (up and down direction) of the low beam unit  31  (namely, the left low beam unit  31   a  and the right low beam unit  31   b ) is represented as a range between a straight line Lb 1  and a straight line Lb 2  shown in  FIG. 1 . A dashed line Lba in  FIG. 1  is a bisector of the angle formed by the straight line Lb 1  and the straight line Lb 2 . 
     An irradiation direction of the low beam unit  31  indicated by the dashed line Lba is changed (adjusted) according to a pitch angle θp of the vehicle  10  by an auto-leveling processing described later. More specifically, the pitch angle θp is an angle formed by a “ground-based horizontal line” and a “vehicular horizontal line.” The ground-based horizontal line is a straight line parallel to a plane including a grounding points of four wheels of the vehicle  10  and extending in a longitudinal direction (namely, front and rear direction) of the vehicle  10 . The vehicular horizontal line is a straight line parallel to a vehicle body (specifically, spring upper member) of the vehicle  10  and extending in the longitudinal direction of the vehicle  10 . 
     In  FIG. 1 , a horizontal line Lh 1  is the ground-based horizontal line, and a horizontal line Lh 2  is the vehicular horizontal line. Hereinafter, an angle formed by the vehicular horizontal line and the dashed line Lba is also referred to as an irradiation angle θb. The auto-leveling processing is a processing for controlling the irradiation angle θb such that an angle formed by the dashed line Lba (namely, the irradiation direction of the low beam unit  31 ) and the ground-based horizontal line coincides with a predetermined antiglare angle θh (an angle θh for preventing a driver of another vehicle from being dazzled). 
     The pitch angle θp is an angle representing a degree (extent) indicative of how much the vehicle  10  (specifically, spring upper member) is leaned (tilted) forward or backward. When the vehicle  10  is neither leaning forward nor backward, the pitch angle θp is “0.” Accordingly, when the pitch angle θp is “0,” the vehicular horizontal line is parallel to the ground-based horizontal line. 
     The pitch angle θp is a positive value (namely, θp&gt;0) when the vehicle  10  is leaning backward. The pitch angle θp is a negative value (namely, θp&lt;0) when the vehicle  10  is leaning forward. In  FIG. 1 , the horizontal line Lh 1  and the horizontal line Lh 2  are parallel to each other, and thus, the pitch angle θp is “0.” 
     A structure of the left low beam unit  31   a  is shown in  FIG. 3 . Notably, a structure of the right low beam unit  31   b  is the same structure as the left low beam unit  31   a , and thus, the right low beam unit  31   b  is not shown. The left low beam unit  31   a  includes a bulb  41 , a reflector  42 , an upper rod  43 , a lower rod  44 , a unit case  45 , and an actuator  46 . The bulb  41  is fixed to the reflector  42 . The reflector  42  is supported by the unit case  45  via the upper rod  43  and the lower rod  44 . An upper portion of the reflector  42  is rotatably supported by a front end portion of the upper rod  43 , and a lower portion of the reflector  42  is rotatably supported by a front end portion of the lower rod  44 . The unit case  45  is fixed to the vehicle body. 
     A length of the lower rod  44  is changed (adjusted) by operation of the actuator  46  (namely, the lower rod  44  advances and retreats axially in the longitudinal direction of the vehicle body), so that the reflector  42  swings (sways) in the vertical direction of the vehicle  10 . Specifically, when the lower rod  44  extends (namely, its front end moves forward), the irradiation angle θb decreases, and thus, a region to be irradiated by the left low beam unit  31   a  moves upward. When the lower rod  44  contracts (namely, its front end moves backward), the irradiation angle θb increases, and thus, the region to be irradiated by the left low beam unit  31   a  moves downward. As described later, the ECU  20  controls the actuator  46 , to thereby control the irradiation angle θb. 
     The camera apparatus  50  is disposed at a position on a cabin side of a front windshield of the vehicle  10  near an unillustrated inner rear-view mirror (a room mirror) fixed at a center upper portion of the front windshield. As shown in  FIG. 2 , the camera apparatus  50  includes an imaging section  51  and an image processing section  52 . The imaging section  51  obtains (captures) an image of a region (scene) in front of the vehicle  10  as a “front image” every time a predetermined time interval Δt elapses, and outputs data (namely, static image data) representing the front image to the image processing section  52 . 
     A captured range (angle of view) in the vertical direction (up and down direction) of the imaging section  51  is represented as a range between a straight line Lc 1  a straight line Lc 2  shown in  FIG. 1 . An angle formed by the straight line Lc 1  and the straight line Lc 2  is a field angle θa. A resolution of the front image in the vertical direction (namely, a number of pixels of which the front image consists in the vertical direction (up and down direction)) is a vertical pixel number Yd. The front image is also referred to as a “travelling direction image” for convenience&#39; sake. 
     The image processing section  52  obtains/acquires a lot of optical flow vectors (hereinafter, also referred to as “flow vectors” for simplification) on the basis of a “latest image” (which is the front image last obtained by the imaging section  51 ) and a “previous image” (which is the front image obtained the time interval Δt before the latest image was obtained). 
     More specifically, the image processing section  52  divides the previous image into rectangles of a predetermined size (namely, treats the previous image as a set of the rectangles), and looks up (searches for) each of the corresponding/respective rectangles in the latest image. When the image processing section  52  finds out the rectangle in the latest image which is same as (or similar to) the rectangle in the previous image, the flow vector whose start point is a position of the rectangle in the previous image and whose end point is a position of the rectangle in the latest image is obtained. Namely, the image processing section  52  obtains the flow vectors by a so-called block matching method. 
     When the flow vectors are obtained, the image processing section  52  obtains an infinity point position Yi indicating an infinity point (FOE) in the front image in the vertical direction (see  FIG. 1 ). The infinity point is a point in the front image representing a straight travelling direction of the vehicle  10  travelling on a flat road. The infinity point position Yi indicates a position of the pixel corresponding to the infinity point. When the infinity point is positioned at the lower end of the front image, the infinity point position Yi is “1.” When the infinity point is positioned at the upper end of the front image, the infinity point position Yi is equal to the vertical pixel number Yd. 
     The infinity point position Yi is also referred to as an “infinity point correlation value” for convenience&#39; sake. A processing for obtaining the infinity point position Yi is also referred to as an “infinity point obtainment processing” for convenience&#39; sake. 
     A method of obtaining the infinity point will be described. An image  71  shown in  FIG. 4  is an example of the front image obtained when the vehicle  10  is travelling straight ahead. A point Pf in  FIG. 4  indicates the infinity point. Each of arrows in the image  71  indicates the flow vector. An (image of) an other vehicle  72  is contained in the image  71 . The other vehicle  72  is travelling in a lane (oncoming lane) opposite to a lane (own lane) in which the vehicle  10  is travelling. 
     In the image  71 , objects contained in the image  71  other than the other vehicle  72  is stationary. As understood from  FIG. 4 , straight lines passing through the start point and the end point of the flow vectors whose start points are not included in the other vehicle  72  (namely, the flow vectors whose start points are included in the stationary objects) pass through the point Pf. Generally, many of the objects in the front image are stationary, and thus, many of the straight lines (vector extended lines) each of which passes through the start point and endpoint of the obtained flow vector pass through the point Pf. 
     In view of this, the image processing section  52  obtains, as the infinity point, a point through which the largest number of the vector extended lines pass among points through which the vector extended lines pass (namely, points at which the vector extended lines intersect with each other). The image processing section  52  outputs the obtained infinity point position Yi to the ECU  20  every time the time interval Δt elapses. 
     Notably, in addition to the ECU  20 , the vehicle  10  is equipped with an ECU (driving support ECU) for detecting (extracting) various objects (for example, another vehicle different from the vehicle  10 , a pedestrian and a position of the own lane) contained in the front image and for providing a “driving support function” which supports the driver of the vehicle  10  on the basis of the detected objects. However, a description related to the driving support function and operation of the driving support ECU is omitted in the present specification. 
     The vehicle height sensor  61  is provided in a suspension apparatus for the rear wheel on a passenger side of the vehicle  10  (see  FIG. 1 ). Specifically, since the vehicle  10  is a right-hand drive vehicle, the vehicle height sensor  61  is provided in the suspension apparatus for the left rear wheel. The vehicle height sensor  61  detects a relative displacement amount of the spring upper member of the vehicle  10  with respect to a rotation axis of the left rear wheel (namely, a displacement amount of a distance between a mounting portion of the suspension apparatus of the left rear wheel in the vehicle body of the vehicle  10  and the rotation axis of the left rear wheel, with respect to a predetermined reference length) as a contraction length Ca, and outputs a signal indicative of the contraction length Ca to the ECU  20 . The contraction length Ca increases as a weight of a load of the vehicle  10  including the driver, an occupant (passenger), and luggage (namely, the vehicle load) increases, on the premise that a position of the center of gravity of the vehicle load does not change (move). 
     The dimmer switch  62  is used/operated by the driver so as to select (change) a lighting state of the headlight  30 . The driver can switch an operation states of the dimmer switch  62  among “OFF Position,” “Low Beam Position” and “High Beam Position.” 
     When the operation state of the dimmer switch  62  is the “Low Beam Position,” the ECU  20  lights (turns on) the low beam unit  31  (namely, the left low beam unit  31   a  and the right low beam unit  31   b ). When the operation state of the dimmer switch  62  is the “High Beam Position,” the ECU  20  lights the low beam unit  31  and the high beam unit  32 . 
     (Auto-Leveling Processing) 
     The ECU  20  executes the auto-leveling processing for making (letting) the angle formed by “the irradiation direction of the low beam unit  31  represented by the dashed line Lba” and “the ground-based horizontal line” coincide with the antiglare angle θh even when the pitch angle θp changes. Namely, the ECU  20  obtains the pitch angle θp, and controls the irradiation angle θb on the basis of the obtained pitch angle θp such that a relationship of a following expression (1) is satisfied. Specifically, the ECU  20  obtains (figures out) a target irradiation angle θbtgt by substituting the obtained pitch angle θp into a following expression (1a), and controls the actuator  46  such that an actual value of the irradiation angle θb is equal to the target irradiation angle θbtgt.
 
θ b=θh+θp   (1)
 
θ btgt=θh+θp   (1a)
 
     A method of obtaining the pitch angle θp will be described. When the standard infinity point position Ystd and the standard pitch angle θstd described later have not been obtained yet, the ECU  20  obtains an estimated (or extrapolated) pitch angle θe by applying the obtained (or detected) contraction length Ca to a relationship between the contraction length Ca and the estimated pitch angle θe, represented by a straight line Le shown in  FIG. 5 . The relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le is stored in the ROM  26  in a form of a map (lookup table). 
     In this case, the ECU  20  figures out the target irradiation angle θbtgt by substituting the estimated pitch angle θe into the expression (1a) as the pitch angle θp. In addition, the ECU  20  controls the actuator  46  such that the actual value of the irradiation angle θb coincides with the target irradiation angle θbtgt. Notably, the ECU  20  calculates a driving amount of the actuator  46  for making (letting) the irradiation angle θb coincide with the target irradiation angle θbtgt by means of applying the target irradiation angle θbtgt to a relationship between the driving amount of the actuator  46  and the irradiation angle θb, the relationship being stored in the ROM  26  in advance, and controls the actuator  46  on the basis of the calculated driving amount. 
     The straight line Le of  FIG. 5  is a straight line determined such that the straight line Le passes through a point Pa 1  and a sum of distances between the straight line Le and each of points Pa 2  to Pa 5  calculated by a least-squares method is minimized. The point Pa 1  indicates the relationship between the contraction length Ca and the pitch angle θp in a case where an occupant (more specifically, an occupant with a predetermined standard weight) is seated only in (on) a driver seat of the vehicle  10  (namely, only the driver is in the vehicle  10 ). The point Pa 2  indicates the relationship between the contraction length Ca and the pitch angle θp in a case where occupants are seated in the driver seat and a front passenger seat. 
     The point Pa 3  indicates the relationship between the contraction length Ca and the pitch angle θp in a case where occupants are seated in all of seats of the vehicle  10 . The point Pa 4  indicates the relationship between the contraction length Ca and the pitch angle θp in a case where the occupants are seated in all the seats of the vehicle  10  and a burden with a predetermined standard weight is loaded in a rear trunk of the vehicle  10 . The point Pa 5  indicates the relationship between the contraction length Ca and the pitch angle θp in a case where the occupant is seated only in the driver seat and the burden with the standard weight is loaded in the rear trunk. 
     As understood from the points Pal to Pa 5 , there is no monotonically increasing relationship between the contraction length Ca and the pitch angle θp. In other words, even if the contraction length Ca is same, the pitch angle θp may differs depending on the position of the center of gravity of the vehicle load. Therefore, there may be a case where a magnitude of a difference between “the estimated/extrapolated pitch angle θe which is obtained by applying the contraction length Ca to the relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le” and “an actual value of the pitch angle θp” is relatively large, depending on the position of the center of gravity of the vehicle load. 
     In view of the forgoing, the ECU  20  obtains the pitch angle θp on the basis of the infinity point position Yi by utilizing a relationship of a monotonic decrease between the pitch angle θp and the infinity point position Yi. Specifically describing about the relationship between the pitch angle θp and the infinity point position Yi, the infinity point position Yi decreases (the infinity point in the front image moves downward) as the pitch angle θp increases (namely, the vehicle  10  leans backward). Meanwhile, the infinity point position Yi increases (the infinity point in the front image moves upward) as the pitch angle θp decreases (namely, the vehicle  10  leans forward). 
     An image base point Yo is defined as the infinity point position Yi obtained when the pitch angle θp is “0.” The image base point Yo is indicated as a point on a line segment Lp which represents a projection plane of the front image in  FIG. 1 . In other words, when the pitch angle θp is “0,” the image base point Yo is an intersection point (base intersection point) between the horizontal line Lh 2  which is the vehicular horizontal line passing through the camera apparatus  50  (specifically, the imaging section  51 ) and the line segment Lp. Namely, when a length of the line segment Lp is treated (regarded) as the vertical pixel number Yd, a length from the lower end of the line segment Lp to the base intersection point corresponds to the image base point Yo. 
     The pitch angle θp whose value is equal to “0,” is also referred to as a “specific angle” for convenience&#39; sake. The image base point Yo is also referred to as a “specific infinity point position” for convenience&#39; sake. 
     When a magnitude |θp| of the pitch angle θp is relatively small, a relationship between the pitch angle θp and the infinity point position Yi is approximately equal to a relationship represented by a following expression (2).
 
θ p=θa ×( Yo−Yi )/ Yd   (2)
 
     It is possible to obtain the image base point Yo in advance. For example, when the vehicle  10  is manufactured or the camera apparatus  50  is exchanged (replaced), the image base point Yo can be obtained on the basis of the front image containing an image of a “target object” which is placed at a predetermined position in front of the vehicle  10 , the front image being obtained (photographed) in a case where the pitch angle θp is set/adjusted to be equal to “0.” However, in many cases, it is not easy to accurately perform an operation (work) of placing the vehicle  10  at a predetermined position in a predetermined direction and of placing the target object at the predetermined position with respect to the vehicle  10 , so that it is not easy to accurately obtain the image base point Yo according to this method. 
     On the other hand, in many cases, many of the objects in the front image are stationary as described above, and thus, it is possible to accurately obtain the infinity point position Yi on the basis of the front image obtained in a case where the vehicle  10  is travelling. In view of this, the ECU  20  obtains the pitch angle θp on the basis of the infinity point position Yi without reference to the image base point Yo. 
     More specifically, the ECU  20  obtains the pitch angle θp, based on a standard pitch angle θstd and a standard infinity point position Ystd. The standard pitch angle θstd is the pitch angle θp at a certain point in time. The standard infinity point position Ystd is the infinity point position Yi at that certain point in time when the pitch angle θp is equal to the standard pitch angle θstd. The standard infinity point position Ystd is also referred to as a “standard infinity point correlation value” for convenience&#39; sake. A following expression (3) is obtained by substituting the standard pitch angle θstd and the standard infinity point position Ystd into the expression (2).
 
θ std=θa ×( Yo−Ystd )/ Yd   (3)
 
     The vehicle  10  in a case where the pitch angle θp is equal to the standard pitch angle θstd is shown in  FIG. 6A . In  FIG. 6A , an angle formed by a horizontal line Lh 3  which is the ground-based horizontal line and a straight line Lf 1  which is the vehicular horizontal line is equal to the standard pitch angle θstd (namely, the pitch angle θp in this case). In this example, the vehicle  10  is leaning forward, and thus, the pitch angle θp is a negative value. 
     Meanwhile, a following expression (4) is obtained by subtracting the expression (3) from the expression (2) (namely, by eliminating the image base point Yo from these expressions).
 
θ p−θstd=θa ×( Ystd−Yi )/ Yd   (4)
 
     The vehicle  10  in a case where the pitch angle θp is different from the standard pitch angle θstd is shown in  FIG. 6B . In  FIG. 6B , an angle formed by a horizontal line Lh 4  which is the ground-based horizontal line and a straight line Lf 2  which is the vehicular horizontal line is the pitch angle θp in this example. A straight line Lst 1  in  FIG. 6B  is a straight line and an angle formed by the straight line Lst 1  and the straight line Lf 2  is the standard pitch angle θstd. In this example, the vehicle  10  is leaning backward, and thus, the pitch angle θp is a positive value. 
     As understood from  FIG. 6B , the expression (4) represents a relationship between (θp−θstd) which is an angle formed by the horizontal line Lh 4  and the straight line Lst 1  and (Ystd−Yi) which is a difference between the standard infinity point position Ystd and the infinity point position Yi. The left member of the expression (4) (namely, θp−θstd) is also referred to as a “third difference value” for convenience&#39; sake. The difference between the standard infinity point position Ystd and the infinity point position Yi (namely, Ystd−Yi) included in the right member of the expression (4) is also referred to as a “fourth difference value” for convenience&#39; sake. 
     A following expression (5) is obtained on the basis of the expression (4). According to the expression (5), it is possible to obtain the pitch angle θp on the basis of the infinity point position Yi, even if the image base point Yo cannot be obtained accurately.
 
θ p=θa ×( Ystd−Yi )/ Yd+θstd   (5)
 
     Next, a method of obtaining the standard pitch angle θstd and the standard infinity point position Ystd will be described. When the vehicle load is the driver only (namely, the occupant is present only in the driver seat of the vehicle  10  and no load (luggage) is loaded on the vehicle  10 ), the contraction length Ca hardly changes, regardless of a weight of the driver. In other words, even if the weight of the driver changes as a result of changing (replacing) the drivers, an amount of change in the contraction length Ca is small and the position of the center of gravity of the vehicle load substantially remains unchanged. 
     In view of this, the ECU  20  obtains, as a pair of the standard pitch angle θstd and the standard infinity point position Ystd, a pair of the estimated pitch angle θe and the infinity point position Yi when the vehicle load is the driver only. 
     Specifically, the ECU  20  stores, as the standard pitch angle θstd in the non-volatile memory  28 , the estimated pitch angle θe obtained by applying the contraction length Ca in a case where the vehicle load is the driver only to the relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le in  FIG. 5 . In addition, the ECU  20  stores the infinity point position Yi in this case as the standard infinity point position Ystd in the non-volatile memory  28 . 
     Notably, when the vehicle  10  has just been manufactured, neither the standard pitch angle θstd nor the standard infinity point position Ystd is stored in the non-volatile memory  28 . In addition, when the camera apparatus  50  is replaced or repaired, the standard pitch angle θstd and the standard infinity point position Ystd are deleted (erased) from the non-volatile memory  28 . 
     The ECU  20  determines that the vehicle load is the driver only, when the contraction length Ca is larger than a predetermined first contraction length C 1  and smaller than a predetermined second contraction length C 2  (namely, C 1 &lt;Ca&lt;C 2 ). The range from the first contraction length C 1  to the second contraction length C 2  is also referred to as a “standard range” for convenience&#39; sake. A condition which is satisfied when the contraction length Ca falls within the standard range is also referred to as a “standard value obtainment condition” for convenience&#39; sake. 
     (Specific Operation) 
     Next, specific operation of the ECU  20  related to the auto-leveling processing will be described. The CPU  25  (hereinafter also referred to as “the CPU” for simplification) of the ECU  20  executes an “auto-leveling processing routine” represented by a flowchart shown in  FIG. 7  every time a predetermined time interval which is shorter than the time interval Δt elapses. 
     Therefore, when an appropriate timing has come, the CPU starts the process from step  700  of  FIG. 7  and proceeds to step  705  so as to determine whether or not the infinity point position Yi has been newly received. Namely, the CPU determines whether or not the infinity point position Yi has been received from the camera apparatus  50  in a period from a time point when the present routine was executed last time to the present time point. 
     If the infinity point position Yi has not been newly received, the CPU makes a “No” determination in step  705  and proceeds to step  795  directly so as to end the present routine. 
     Meanwhile, if the infinity point position Yi has been newly received, the CPU makes a “Yes” determination in step  705  and proceeds to step  710  so as to obtain the contraction length Ca detected by the vehicle height sensor  61 . Subsequently, the CPU proceeds to step  715  so as to obtain the estimated (or extrapolated) pitch angle θe by applying the contraction length Ca to the relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le in  FIG. 5 . 
     Furthermore, the CPU proceeds to step  720  so as to determine whether or not the contraction length Ca falls within the range between the first contraction length C 1  and the second contraction length C 2  (namely, the contraction length Ca is included in the standard range). 
     If the contraction length Ca falls within the range between the first contraction length C 1  and the second contraction length C 2 , the CPU makes a “Yes” determination in step  720  and proceeds to step  725  so as to store the infinity point position Yi in the non-volatile memory  28  as the standard infinity point position Ystd. Subsequently, the CPU proceeds to step  730  so as to store the estimated pitch angle θe in the non-volatile memory  28  as the standard pitch angle θstd. Processing for obtaining the standard pitch angle θstd and the standard infinity point position Ystd (namely, the standard infinity point correlation value) is also referred to as a “standard value obtainment processing” for convenience&#39; sake. Furthermore, the CPU proceeds to step  735 . 
     Meanwhile, if the contraction length Ca does not fall within the range between the first contraction length C 1  and the second contraction length C 2 , the CPU makes a “No” determination in step  720  and proceeds to step  735  directly. 
     In step  735 , the CPU determines whether or not the standard infinity point position Ystd and the standard pitch angle θstd have been obtained. Namely, the CPU determines whether or not the standard infinity point position Ystd and the standard pitch angle θstd have been stored (or obtained and stored) in the non-volatile memory  28 . 
     If the standard infinity point position Ystd and the standard pitch angle θstd have been obtained, the CPU makes a “Yes” determination in step  735  and proceeds to step  740  so as to obtain the pitch angle θp on the basis of the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi. Specifically, the CPU obtains (figures out) the pitch angle θp by substituting the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi into the expression (5) described above. Processing for obtaining the pitch angle θp on the basis of the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi is also referred to as a “pitch angle estimation (or extrapolation) processing” for convenience&#39; sake. Subsequently, the CPU proceeds to step  750 . 
     Meanwhile, if the standard infinity point position Ystd and the standard pitch angle θstd have not been obtained, the CPU makes a “No” determination in step  735  and proceeds to step  745  so as to set the pitch angle θp to a value equal to the estimated pitch angle θe, Namely, the CPU obtains the value equal to the estimated pitch angle θe as the pitch angle θp. Subsequently, the CPU proceeds to step  750 . 
     In step  750 , the CPU determines whether or not the low beam unit  31  is On (namely, being turned on). Namely, the CPU determines whether or not the operation state of the dimmer switch  62  is either the “Low Beam Position” or the “High Beam Position.” 
     If the low beam unit  31  is On, the CPU makes a “Yes” determination in step  750  and proceeds to step  755  so as to control the irradiation angle θb. More specifically, the CPU obtains (figures out) the target irradiation angle θbtgt by substituting the pitch angle θp into the expression (1a) described above. In addition, the CPU controls the actuator  46  such that the actual value of the irradiation angle θb coincides with the target irradiation angle θbtgt. Subsequently, the CPU proceeds to step  795 . 
     Meanwhile, if the low beam unit  31  is not θn, the CPU makes a “No” determination in step  750  and proceeds to step  795  directly. 
     First Modification of First Embodiment 
     Next, the headlight control apparatus according to a first modification of the first embodiment of the present disclosure (hereinafter also referred to as the “first modification apparatus”) will be described. The first control apparatus described above obtains the pitch angle θp on the basis of the standard infinity point position Ystd and the standard pitch angle θstd which have been obtained when the contraction length Ca fell within (was included in) the standard range. In contrast, the first modification apparatus obtains the pitch angle θp on the basis of the standard pitch angle θstd and a reference pitch angle θref which have been obtained when the contraction length Ca fell within the standard range. Hereinafter, this difference will be mainly described. 
     A headlight control ECU  21  (hereinafter also referred to as the “ECU  21 ” for simplification) according to the first modification apparatus obtains the standard pitch angle θstd and the reference pitch angle θref when the contraction length Ca fell within the standard range (namely, it is determined that the vehicle load is the driver only). In addition, the ECU  21  stores those of the standard pitch angle θstd and the reference pitch angle θref in the non-volatile memory  28 . The reference pitch angle θref is also referred to as the “standard infinity point correlation value” for convenience&#39; sake. When the contraction length Ca does not fall within the standard range, the ECU  21  obtains the pitch angle θp on the basis of the standard pitch angle θstd and the reference pitch angle θref. 
     This method of obtaining the pitch angle θp will be specifically described with reference to  FIG. 8 . When the contraction length Ca falls within the standard range, the ECU  21  figures out a current pitch angle θn by substituting the infinity point position Yi and the image base point Yo which has been obtained and stored in the non-volatile memory  28  in advance into a following expression (6). The current pitch angle θn is also referred to as the “infinity point correlation value” for convenience&#39; sake. The expression (6) represents the same relationship as the expression (2) described above.
 
θ n=θa ×( Yo−Yi )/ Yd   (6)
 
     In addition, the ECU  21  obtains a value equal to the current pitch angle θn as the reference pitch angle θref. By treating the infinity point position Yi in this case as the standard infinity point position Ystd, a relationship represented by a following expression (7) is satisfied.
 
θ ref=θa ×( Yo−Ystd )/ Yd   (7)
 
     Furthermore, the ECU  21  obtains the estimated pitch angle θe by applying the contraction length Ca to the relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le. In addition, the ECU  21  obtains a value equal to the estimated pitch angle θe as the standard pitch angle θstd. 
     An example of a case where the standard pitch angle θstd and the reference pitch angle θref have been obtained and the contraction length Ca does not fall within the standard range is shown in  FIG. 8 . In  FIG. 8 , an angle formed by a horizontal line Lh 5  which is the ground-based horizontal line and a straight line Lf 3  which is the vehicular horizontal line is the pitch angle θp in the present example. A straight line Lst 2  in  FIG. 8  is a straight line and an angle formed by the straight line Lst 2  and the straight line Lf 3  is the standard pitch angle θstd. In the present example, the vehicle  10  is leaning backward, and thus, the pitch angle θp is a positive value. 
     When the contraction length Ca does not fall within the standard range, the ECU  21  figures out the current pitch angle θn on the basis of the expression (6) and figures out a displacement pitch angle θfoe by substituting that the current pitch angle θn into a following expression (8). In  FIG. 8 , the displacement pitch angle θfoe is an angle formed by the horizontal line Lh 5  and the straight line Lf 3 . In other words, the displacement pitch angle θfoe is a difference between “the pitch angle θp at a point in time when the standard pitch angle θstd and the reference pitch angle θref were obtained” and “the pitch angle θp at the present time.”
 
θ foe=θn−θref   (8)
 
     In addition, the ECU  21  obtains (figures out) the pitch angle θp on the basis of a following expression (9).
 
θ p=θfoe+θstd   (9)
 
     A reason for obtaining the pitch angle θp on the basis of the displacement pitch angle θfoe will now be described. A following expression (10) is obtained on the basis of the expression (6) to (9). 
     
       
         
           
             
               
                 
                   
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     In many cases, a magnitude of a difference between the standard pitch angle θstd obtained in a case where it was determined that the vehicle load was the driver only and the actual value of the pitch angle θp at that point in time is small. Meanwhile, there is a high possibility that a magnitude of a difference between “the reference pitch angle θref obtained at the point in time when the standard pitch angle θstd was obtained” and “the actual value of the pitch angle θp at that point in time” is relatively large, since that reference pitch angle θref is figured out on the basis of the image base point Yo. 
     Furthermore, there is a high possibility that a magnitude of a difference between the current pitch angle θn obtained at the present time and the actual value of the pitch angle θp at the present time is relatively large, since that current pitch angle θn, similarly to the reference pitch angle θref, is figured out on the basis of the image base point Yo. However, the displacement pitch angle θfoe is set to a value equal to a difference between the current pitch angle θn at the present time and the reference pitch angle θref, so that an error caused by an accuracy in obtainment of the image base point Yo is canceled out. 
     In other words, the displacement pitch angle θfoe indicates a difference between the pitch angle θp at the present time and the standard pitch angle θstd accurately. Therefore, according to the first modification apparatus, even if the image base point Yo has not been obtained accurately, it is possible to accurately obtain the pitch angle θp at the present time on the basis of the expression (9). 
     (Specific Operation) 
     Next, specific operation of the ECU  21  related to the auto-leveling processing will be described. The CPU  25  (hereinafter also referred to as “the CPU” for simplification) of the ECU  21  executes the “auto-leveling processing routine” represented by a flowchart shown in  FIG. 9  every time a predetermined time interval which is shorter than the time interval Δt elapses. 
     Notably, each step shown in  FIG. 9  at which the same processing is performed as each step shown in  FIG. 7  is given the same step symbol as one given to such step shown in  FIG. 7 . 
     When an appropriate timing has come, the CPU starts the process from step  900  of  FIG. 9  and proceeds to step  705 . After executing the process in step  715 , the CPU proceeds to step  917  so as to obtain (figure out) the current pitch angle θn on the basis of the expression (6) described above (namely, on the basis of the image base point Yo and the infinity point position Yi). Subsequently, the CPU proceeds to step  720 . 
     When the “Yes” determination is made in step  720  (namely, the contraction length Ca falls within the standard range), the CPU proceeds to step  925  so as to store the current pitch angle θn as the reference pitch angle θref in the non-volatile memory  28 . Subsequently, the CPU proceeds to step  730  so as to store the estimated pitch angle θe as the standard pitch angle θstd in the non-volatile memory  28 . Processing for obtaining the standard pitch angle θstd and the reference pitch angle θref (namely, the standard infinity point correlation value) is also referred to as the “standard value obtainment processing” for convenience&#39; sake. Furthermore, the CPU proceeds to step  935 . 
     Meanwhile, when the “no” determination is made in step  720 , the CPU proceeds to step  935  directly. 
     In step  935 , the CPU determines whether or not the standard pitch angle θstd and the reference pitch angle θref have been obtained. Namely, the CPU determines whether or not the standard pitch angle θstd and the reference pitch angle θref have been stored in the non-volatile memory  28 . 
     If the standard pitch angle θstd and the reference pitch angle θref have been obtained, the CPU makes a “Yes” determination in step  935  and proceeds to step  940  so as to obtain the displacement pitch angle θfoe on the basis of the expression (8) described above. Subsequently, the CPU proceeds to step  942  so as to obtain the pitch angle θp on the basis of the expression (9) described above. Processing for obtaining the pitch angle θp on the basis of the reference pitch angle θref, the standard pitch angle θstd and the current pitch angle θn is also referred to as the “pitch angle estimation processing” for convenience&#39; sake. Furthermore, the CPU proceeds to step  750 . 
     Meanwhile, if the standard pitch angle θstd and the reference pitch angle θref have not been obtained, the CPU makes a “No” determination in step  935  and proceeds to step  745 . 
     Second Modification of First Embodiment 
     Next, the headlight control apparatus according to a second modification of the first embodiment of the present disclosure (hereinafter also referred to as the “second modification apparatus”) will be described. The first control apparatus described above obtains the pitch angle θp on the basis of the expression (5) described above. In contrast, the second modification apparatus is different from the first control apparatus only in that the pitch angle θp is obtained on the basis of an expression (14) described later. Hereinafter, this difference will be mainly described. 
     As understood from a rectangular triangle defined by the horizontal line Lh 4 , the straight line Lf 2  and the line segment Lp shown in  FIG. 6B  (in which the horizontal line Lh 4  and the line segment Lp are perpendicular to each other), a relationship among the pitch angle θp, the image base point Yo and the infinity point position Yi is represented by a following expression (11). In the expression (11), K is a positive constant.
 
tan(θ p )= K ×( Yo−Yi )  (11)
 
     A following expression (12) is obtained by substituting the standard pitch angle θstd and the standard infinity point position Ystd into the expression (11).
 
tan(θ std )= K ×( Yo−Ystd )  (12)
 
     Furthermore, a following expression (13) is obtained by subtracting the expression (12) from the expression (11) (namely, by eliminating the image base point Yo from these expressions). Accordingly, it is possible to obtain the pitch angle θp on the basis of a following expression (14). More specifically, a headlight control ECU  22  according to the second modification apparatus obtains (figures out) the pitch angle θp by substituting the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi into the expression (14), when the process in step  740  of  FIG. 7  is executed. The left member of the expression (13) (namely, tan(θp)−tan(θstd)) is also referred to as a “first difference value” for convenience&#39; sake. The difference between the standard infinity point position Ystd and the infinity point position Yi (namely, Ystd−Yi) included in the right member of the expression (13) is also referred to as a “second difference value” for convenience&#39; sake.
 
tan(θ p )−tan(θ std )= K ×( Ystd−Yi )  (13)
 
tan(θ p )= K ×( Ystd−Yi )+tan(θ std )  (14)
 
     Second Embodiment 
     Next, a second embodiment of the present disclosure will be described. The first control apparatus described above obtains the standard infinity point position Ystd and the standard pitch angle θstd when the field angle θa falls within the standard range. Meanwhile, the headlight control apparatus according to the second embodiment (hereinafter also referred to as the “second control apparatus”) obtains the standard infinity point position Ystd and the standard pitch angle θstd when the contraction length Ca is smaller than a value obtained by subtracting a predetermined difference threshold α (positive constant) from a standard contraction length Cstd (namely, Ca&lt;Cstd−α). Hereinafter, this difference will be mainly described. 
     The standard contraction length Cstd is set to a value equal to the contraction length Ca of when the standard infinity point position Ystd and the standard pitch angle θstd are obtained. In other words, the standard infinity point position Ystd and the standard pitch angle θstd are newly obtained (updated) every time the contraction length Ca becomes smaller than a value obtained by subtracting the difference threshold α from the standard contraction length Cstd. In addition, the contraction length Ca at that point in time is newly obtained as the standard contraction length Cstd (namely, the standard contraction length Cstd is updated). A condition which is satisfied when the contraction length Ca is smaller than a value obtained by subtracting the difference threshold α from the standard contraction length Cstd is also referred to as a “standard value obtainment condition” for convenience&#39; sake. 
     The standard contraction length Cstd stored in the non-volatile memory  28  at the time of manufacturing the vehicle  10  is equal to a predetermined contraction length initial value Ci. The contraction length initial value Ci is larger than a value obtained by adding the difference threshold α to a maximum contraction length Cmax (namely, Cmax+α&lt;Ci). The maximum contraction length Cmax is approximately equal to an upper limit of a range of the contraction length Ca detected by the vehicle height sensor  61 . Notably, when the camera apparatus  50  is replaced or repaired, the standard contraction length Cstd is set to the contraction length initial value Ci. 
     The contraction length Ca which is obtained when the vehicle  10  is travelling for the first time after the vehicle  10  was manufactured is smaller than a value obtained by subtracting the difference threshold α from the contraction length initial value Ci, so that the standard value obtainment condition is satisfied. Accordingly, at this time, the contraction length Ca is obtained (stored) as the standard contraction length Cstd, and the standard infinity point position Ystd and the standard pitch angle θstd are obtained. Thereafter, when the contraction length Ca becomes smaller than a value obtained by subtracting the difference threshold α from the stored standard contraction length Cstd, the standard infinity point position Ystd and the standard pitch angle θstd are newly obtained. 
     The difference threshold α is, for example, a small value as compared with a change amount of the contraction length Ca in a case where the number of occupants in the vehicle  10  decreases, and determined in advance such that the standard value obtainment condition cannot be repeatedly satisfied while the vehicle  10  is travelling when/while the vehicle load has not changed 
     (Specific Operation) 
     Next, specific operation of a headlight control ECU  23  (hereinafter also referred to as the “ECU  23 ” for simplification) according to the second embodiment will be described. The CPU  25  (hereinafter also referred to as “the CPU” for simplification) of the ECU  23  executes the “auto-leveling processing routine” represented by a flowchart shown in  FIG. 10  every time a predetermined time interval which is shorter than the time interval Δt elapses. 
     Notably, each step shown in  FIG. 10  at which the same processing is performed as each step shown in  FIG. 7  is given the same step symbol as one given to such step shown in  FIG. 7 . 
     When an appropriate timing has come, the CPU starts the process from step  1000  of  FIG. 10  and proceeds to step  705 . After executing the process in step  715 , the CPU proceeds to step  1020  so as to determine whether or not the contraction length Ca is smaller than a value obtained by subtracting the difference threshold α from the standard contraction length Cstd. 
     When the contraction length Ca is smaller than a value obtained by subtracting the difference threshold α from the standard contraction length Cstd, the CPU makes a “Yes” determination in step  1020  and proceeds to step  1022  so as to store the contraction length Ca as the standard contraction length Cstd in the non-volatile memory  28 . Subsequently, the CPU proceeds to step  725 . 
     Meanwhile, the contraction length Ca is equal to or larger than a value obtained by subtracting the difference threshold α from the standard contraction length Cstd, the CPU makes a “No” determination in step  1020  and proceeds to step  735  directly. 
     After executing the processing of step  755 , the CPU proceeds to step  1095  directly so as to end the present routine. In addition, if the determination condition of step  705  is not satisfied (namely, the infinity point position Yi has not been newly received), the CPU makes a “No” determination in step  705  and proceeds to step  1095  directly. 
     Modification of Second Embodiment 
     Next, the headlight control apparatus according to a modification of the second embodiment of the present disclosure (hereinafter also referred to as the “third modification apparatus”) will be described. The second control apparatus described above obtains the pitch angle θp on the basis of the standard infinity point position Ystd and the standard pitch angle θstd which have been obtained when the standard value obtainment condition was satisfied. In contrast, similar to the first modification apparatus described above, the third modification apparatus obtains the pitch angle θp on the basis of the standard pitch angle θstd and the reference pitch angle θref which have been obtained when the standard value obtainment condition was satisfied. 
     The CPU  25  (hereinafter also referred to as “the CPU” for simplification) of a headlight control ECU  24  (hereinafter also referred to as the “ECU  24 ” for simplification) according to the third modification apparatus executes the “auto-leveling processing routine” represented by a flowchart shown in  FIG. 11  every time a predetermined time interval which is shorter than the time interval Δt elapses. 
     Notably, each step shown in  FIG. 11  at which the same processing is performed as each step shown in  FIG. 7  is given the same step symbol as one given to such step shown in  FIG. 7 . Similarly, each step shown in  FIG. 11  at which the same processing is performed as each step shown in  FIG. 9 or 10  is given the same step symbol as one given to such step shown in  FIG. 9 or 10 . 
     When an appropriate timing has come, the CPU starts the process from step  1100  of  FIG. 11  and proceeds to step  705 . After executing the processing in step  917 , the CPU proceeds to step  1020 . After executing the processing in step  1022 , the CPU proceeds to step  925 . 
     After executing the processing in step  755 , the CPU proceeds to step  1195  so as to end the present routine. In addition, when the determination condition of step  705  is not satisfied (namely, the infinity point position Yi has not been newly received), the CPU makes a “No” determination in step  705  and proceeds to step  1195  directly. 
     As having been described above, the first control apparatus and the second control apparatus can obtain the pitch angle θp on the basis of the contraction length Ca detected by the vehicle height sensor  61  and the infinity point position Yi obtained by the camera apparatus  50 . In other words, according to the first control apparatus and the second control apparatus, even if the vehicle height sensor  61  is provided in the suspension apparatus only for the rear wheel, the pitch angle θp can be obtained by means of using the camera apparatus  50  equipped for providing the driving support function. 
     Especially, according to the first control apparatus (and, the first modification apparatus and the second modification apparatus), it is possible to accurately obtain the pitch angle θp on the basis of the standard pitch angle and the standard infinity point correlation value obtained when the contraction length Ca falls within the standard range. According to the second control apparatus (and the third modification apparatus), the standard pitch angle and the standard infinity point correlation value are obtained early after the vehicle  10  was manufactured, and thus, it is possible to expand opportunities for obtaining the pitch angle θp on the basis of the standard pitch angle and the standard infinity point correlation value. 
     The embodiments of the headlight control apparatus according to the present disclosure have been described; however, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the disclosure. For example, according to the present embodiments, the image processing section  52  obtains the infinity point position Yi. However, the infinity point position Yi may be obtained by the ECU  20 . In this case, the image processing section  52  may be configured to output/transmits data (namely, static image data) representing the front image to the ECU  20  every time the time interval Δt elapses. 
     In addition, the image processing section  52  according to the present embodiments outputs/transmits the infinity point position Yi every time the time interval Δt elapses. However, the image processing section  52  may be configured not to output/transmit the infinity point position Yi to the ECU  20  when the infinity point position Yi cannot be obtained accurately (for example, in a case where the vehicle  10  is not travelling (moving)). 
     In addition, the ECU  20  according to the first control apparatus obtains the pitch angle θp on the basis of the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi if the standard infinity point position Ystd and the standard pitch angle θstd have been obtained (namely, in a case where the “Yes” determination is made in step  735 ), regardless of whether or not the contraction length Ca falls within the standard range. Namely, in this case, the ECU  20  executes the process in  740 . However, when the contraction length Ca falls within the standard range, the ECU  20  may obtain the pitch angle θp by executing a process different from that in step  740 . For example, in this case, the ECU  20  may obtain a value equal to the estimated pitch angle θe obtained by executing the process in step  715  as the pitch angle θp. 
     In addition, the ECU  20  according to the first control apparatus determines that the vehicle load is the driver only when the contraction length Ca is larger than the first contraction length C 1  and smaller than the second contraction length C 2 . In other words, the first contraction length C 1  has been set to a value approximately equal to a lower limit of a range of the contraction length Ca in a case where the vehicle load is the driver only. However, the first contraction length C 1  may be set to a value approximately equal to the contraction length Ca in a case where there is no vehicle load in the vehicle  10 . 
     In addition, the ECU  23  according to the second control apparatus obtains the pitch angle θp by substituting the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi into the expression (5) described above (see step  740  in  FIG. 10 ). However, the ECU  23  may be configured to obtain the pitch angle θp by substituting the standard infinity point position Ystd, the standard pitch angle θstd and the infinity point position Yi into the expression (14). 
     In addition, the specific angle according to the present embodiments is “0.” However, the specific angle may be a value different from “0.” In this case, the image base point Yo is a value equal to the infinity point position Yi obtained when the pitch angle θp is equal to that specific angle different from “0.” 
     In addition, the difference threshold α according to the second embodiments is a positive constant. However, the difference threshold α may be set to “0.” 
     In addition, the ECU  20  according to the first embodiment obtains the standard pitch angle θstd by applying the contraction length Ca to the relationship between the contraction length Ca and the estimated pitch angle θe represented by the straight line Le when the contraction length Ca falls within the standard range. However, the ECU  20  may obtain the standard pitch angle θstd by applying the contraction length Ca to a relationship (specific relationship; nonlinear relationship obtained and stored in advance) between the contraction length Ca and the estimated pitch angle θe different from the relationship represented by the straight line Le when the contraction length Ca falls within the standard range. 
     In this case, the ECU  20  stores the specific relationship in the non-volatile memory  28  and obtains the standard pitch angle θstd by applying the contraction length Ca to the specific relationship when the contraction length Ca falls within the standard range. For example, the specific relationship may be obtained on the basis of a plurality of combinations of the contraction length Ca and the pitch angle θp obtained (measured) in various cases where the vehicle load is a driver only and each of drivers with different weights from each other is seated one by one. 
     In addition, in the present embodiments, the irradiation angle θb is changed (controlled) by the operation of the actuator  46 . However, the irradiation angle θb may be changed by a method different from this. For example, the low beam unit  31  may be configured such that a region irradiated by the bulb  41  is changed as a position of a shielding plate disposed in front of the bulb  41  is changed. In this case, the irradiation angle θb is changed as the position of the shielding plate is changed. 
     In addition, the vehicle height sensor  61  according to the present embodiments is provided in the suspension apparatus for the rear wheel on the passenger side of the vehicle  10 . However, two of vehicle height sensors may be provided in the suspension apparatuses for both of the rear wheels respectively. In this case, the ECU  20  may be configured to obtain an average of the values detected by the two vehicle height sensors as the contraction length Ca. Alternatively, the vehicle height sensor  61  may be provided in the suspension apparatus for the front wheel of the vehicle  10 . 
     In addition, the first control apparatus and the second control apparatus obtain the pitch angle θp regardless of whether or not the low beam unit  31  is θn. However, the ECU  20  may be configured to obtain the pitch angle θp only when the low beam unit  31  is θn. 
     In addition, the camera apparatus  50  according to the present embodiments obtains the image of the region in front of the vehicle  10 . However, the camera apparatus  50  may be disposed on the vehicle  10  so as to obtain an image of a region behind the vehicle  10  in addition to the region in front of the vehicle  10 .