Apparatus for automatically adjusting optical axis of vehicle headlights

This application is based on and incorporates herein by reference Japanese Patent Application NO. 2000-303282 filed on Oct. 3, 2000.

The present invention relates to an automatic vehicle headlight optical axis adjusting apparatus for automatically adjusting the optical axis of illumination from headlights provided in a vehicle.

It is proposed to ensure forward visibility of a vehicle by measuring distance to a preceding vehicle ahead thereof using a laser radar device and adjusting the optical axis of headlights up to the extent that the headlights do not blind a driver of a vehicle far ahead.

In one system disclosed in JP-A-10-151987, light distribution is changed so as to avoid directing the illumination light of the headlights to the detected preceding vehicle. However, in order to change part of the light distribution of the headlights the headlights and associated structure unavoidably become complicated and expensive. In addition, drivers of preceding vehicles to the right and left sides are blinded due to the light distribution characteristics of the headlights if the optical axis of the headlights is raised according to the distance to the vehicle that is directly ahead of the vehicle.

The present invention therefore has an object to provide an apparatus for automatically adjusting an optical axis of vehicle headlights so that forward visibility can be improved.

According to the present invention, distance to a forward or preceding vehicle in plural side-to-side zones of a specific angular range is detected as forward information for the vehicle. The desired optical axis raising angle for a vehicle headlight is calculated according to these inter-vehicle distances. The desired optical axis raising angle is the most downward pointing angle. It is therefore possible to control upward optical axis adjustment without complicating a system configuration and without blinding a driver of a preceding vehicle, and forward visibility can be improved by appropriately controlling adjustment of the optical axis of the headlight.

Preferably, a modular laser radar device is used to scan a specific angular range side to side for information in front of the vehicle, all preceding vehicles in the angular range can be detected.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic view showing an apparatus for automatically adjusting an optical axis of vehicle headlights according to a preferred embodiment of the present invention;

FIG. 2 is a section view showing a headlight shown in FIG. 1;

FIG. 3 is a flow chart showing a process for controlling raising the optical axis executed by an electronic control unit (ECU) shown in FIG. 1;

FIG. 4 is a diagrammatic view showing the headlight illumination area and inter-vehicle distance to a preceding vehicle in each zone; and

FIGS. 5A to 5 C are graphs showing desired optical axis raising angles in relations to inter-vehicle distances in each zone in FIG. 3 .

Referring to FIG. 1, a front wheel vehicle height sensor 11 F and rear wheel vehicle height sensor 11 R are mounted on the front and rear driver's side or passenger side axle of the vehicle, respectively. The relative displacement of the front wheel axle and the rear wheel axle to the chassis, that is, front vehicle height HF (vehicle height displacement at the front axle) and rear vehicle height HR (vehicle height displacement at the rear axle), are input from these vehicle height sensors 11 F and 11 R together with sensor signals from other types of sensors to an ECU (electronic control unit) 20 mounted in the vehicle. It is noted that the ECU 20 is shown outside the vehicle in the figure.

The ECU 20 is a logic operator comprising a CPU (central processing unit) 21 for executing various processes, ROM 22 for storing a control program and fixed control data, RAM 23 for storing data temporarily, backup RAM 24 , input/output circuit 25 , and a bus line 26 for connecting these components. The output signal from the ECU 20 is input to actuators 35 L and 35 R for the left and right headlights 30 L and 30 R to adjust the optical axis of the left and right headlights 30 L and 30 R. A laser radar device 40 for scanning a specific left and right angular width to detect all preceding vehicles within a specific range is mounted in the front bumper area of the vehicle, for example, to input distance to a vehicle detected by the laser radar device 40 to the ECU 20 as forward information for adjustably controlling the optical axis of the headlights 30 L and 30 R.

In FIG. 2, the headlight 30 L ( 30 R) comprises primarily a lamp 31 and a reflector 32 securing the lamp 31 , a rod-like support 33 for supporting the reflector 32 movably so as to roll freely in an arc in the direction of the arrow, another rod-like moving part 34 that is freely movable while also supporting the reflector 32 , and an actuator 35 L ( 35 R) such as a stepper motor or d.c. motor for driving the moving part 34 back and forth in the direction of the arrow. As a result, the reflector 32 pivots on the end of the support 33 when the moving part 34 is driven forward or backward by the actuator 35 L ( 35 R) and is tilted upward or downward by a desired optical axis angle (desired optical axis adjustment angle) Ga to adjust the optical axis of the headlight 30 L ( 30 R). It should be noted that the optical axis of the headlight 30 L ( 30 R) is initially set assuming that a driver is onboard the vehicle.

The front-rear pitch angle θp of the vehicle is calculated using the following equation (1) as inclination to a predefined reference surface in the front-rear direction of the vehicle based on the front vehicle height HF and rear vehicle height HR input from the vehicle height sensors 11 F, 11 R. Here, Lw is a wheel base (distance between the axles) of front and rear wheels of the vehicle.

θp=tan −1 {(HF−HR)/Lw}  (1)

The desired optical axis angle θa is then calculated with respect to this pitch angle θp so that θa ≡−θp and does not blind a driver of an on-coming vehicle. It will be noted that the desired optical axis angle θa for normal control of the headlight 30 L ( 30 R) is maintained at a downward 1[%] (≡−0.57[deg]) angle so that drivers of preceding vehicles are not blinded and forward visibility can be ensured for the driver of the vehicle having a vehicle headlight optical axis adjusting apparatus of the present invention.

The process executed by the CPU 21 of the ECU 20 for controlling raising the optical axis of the headlights 30 L and 30 R is described next below based on the flow chart shown in FIG. 3 . This control routine is repeated by the CPU 21 at specific time intervals.

Referring to FIG. 3, the output signal from the laser radar device 40 is read first at step S 101 as forward information for the vehicle. Inter-vehicle distance D 1 , D 2 , and D 3 is then calculated at the next step S 102 for each zone Z 1 , Z 2 , Z 3 preset for the vehicle as shown in FIG. 4 based on the output signal from the laser radar device 40 read at step S 101 . It is noted that, as shown by the dotted line in FIG. 4, the illumination area resulting from the light distribution characteristics of the headlights 30 L and 30 R does not cause on-coming vehicles at a distance on the right side to be illuminated, but does illuminate vehicles at a distance directly ahead and on the left side. This means that the angle allowed for adjusting the optical axis of the headlights 30 L, 30 R upward varies according to where the forward vehicle is located even when the distance to the forward vehicle is the same.

Next, at step S 103 , desired optical axis raising angle θH 1 , θH 2 , θH 3 is calculated from the maps shown in FIGS. 5A to 5 C according to the inter-vehicle distances D 1 , D 2 , and D 3 determined at step S 102 . More specifically, desired optical axis raising angle θH 1 [deg] for inter-vehicle distance D 1 [m] in zone Z 1 is determined from the map of FIG. 5A, desired optical axis raising angle θH 2 [deg] for inter-vehicle distance D 2 [m] in zone Z 2 is determined from the map of FIG. 5B, and desired optical axis raising angle θH 3 [deg] for inter-vehicle distance D 3 [m] in zone Z 3 is determined from the map of FIG. 5 C.

It is assumed that the inter-vehicle distance D 1 to vehicle A in zone Zi in FIG. 4 id 90[m], inter-vehicle distance D 2 to vehicle B in zone Z 2 is 110[m], and inter-vehicle distance D 3 to vehicle C in zone Z 3 is 80[m]. In this case, desired optical axis raising angle θH 1 for inter-vehicle distance D 1 =90[m] to vehicle A in zone Z 1 is determined to be 0.4[deg] from the map data of FIG. 5A, desired optical axis raising angle θH 2 for inter-vehicle distance D 2 =110[m] to vehicle B in zone Z 2 is determined to be 0.3[deg] from the map data of FIG. 5B, and desired optical axis raising angle θH 3 for inter-vehicle distance D 3 =80[m] to vehicle C in zone Z 3 is determined to be 0[deg] from the map data of FIG. 5 C. This map data is stored in ROM 22 of ECU 20 .

Moving next to step S 104 , the smallest of the desired optical axis raising angles θH 1 , θH 2 , θH 3 calculated at step S 103 is selected. In the above example 0[deg] is selected as the smallest desired optical axis raising angle. This is because in this case it is necessary to give more consideration to blinding a driver of vehicle C on the left side in zone Z 3 than vehicle B directly ahead in zone Z 2 , and the optical axis is therefore not raised.

If in this example there is no vehicle C or other vehicle on the left side in zone Z 3 ahead of vehicle B directly ahead in zone Z 2 , the desired optical axis raising angle θH 3 for the inter-vehicle distance D 3 =∞[m] in zone Z 3 determined by the map data search at step S 103 is 0.5[deg]. As a result, 0.3[deg] will be selected as the smallest of the desired optical axis raising angles θH 1 , θH 2 , θH 3 . This is because in this case vehicle A on the right side in zone Z 1 is closer than vehicle B directly ahead in zone Z 2 , but forward visibility can be improved by controlling the optical axis upward considering the illumination range of the headlights 30 L, 30 R. Finally at step S 105 , the actuator 35 L, 35 R is driven according to the smallest desired optical axis raising angle selected at step S 104 , thereby controlling the optical axis of the headlight 30 L, 30 R.

It is noted that, if the distance to the preceding vehicles is not divided into zones position information would be needed for all preceding vehicles. Because position information for preceding vehicles can be obtained by communication with an adaptive cruise control ECU (not shown) of the laser radar device 40 , it would be necessary to communicate 20 bytes if, for example, there are ten preceding vehicles. Further, 1 byte is needed for the right to left distance, and 1 byte is needed for the distance ahead. This increases the communication load. By dividing the position information for preceding vehicles into zones as in the above embodiment and outputting the inter-vehicle distances D 1 , D 2 , D 3 in sequence, however, the information communicated from the adaptive cruise control ECU that is needed to control raising the optical axis is only 3 bytes (=1 byte×3).

According to the above embodiment, the inter-vehicle distance D 1 , D 2 , D 3 to the vehicle A, B, C ahead in each of three zones Z 1 , Z 2 , Z 3 dividing the area ahead of the vehicle side to side into predetermined zones of a specific angular range is detected by the laser radar device 40 to obtain the forward information for the vehicle. The desired optical axis raising angle θH 1 , θH 2 , θH 3 for the vehicle headlight 30 L, 30 R is calculated according to these inter-vehicle distances D 1 , D 2 , D 3 . The optical axis of the headlight 30 L, 30 R is adjusted to the most downward pointing angle selected from among these desired optical axis raising angles θH 1 , θH 2 , θH 3 .

It is therefore possible to control optical axis adjustment without complicating the system configuration and without blinding a driver of a preceding vehicle, and forward visibility can be improved by appropriately controlling adjustment of the optical axis of the headlight 30 L, 30 R upward from the desired optical axis angle Oa used during normal control.

It will be noted that in place of the laser radar device 40 a millimeter wave radar device or CCD camera and image data processing system may be used to detect the forward information for the vehicle and control raising the optical axis of the headlight 30 L, 30 R.

It will be noted also that in place of dividing the area ahead of the vehicle into three zones, a minimum of two zones can be used assuming that the illumination ranges resulting the light distribution characteristics are different on right and left.

Furthermore, the desired optical axis raising angles need not be set in steps as shown in FIGS. 5A to 5 C, but may be determined linearly or non-linearly. Furthermore, the desired optical axis raising angle may be set to decrease as the zone gets closer to the right because the preceding embodiment assumes driving on the left side.

The present invention should not be limited to the above embodiment and modifications, but may be implemented in many other ways without departing from the spirit of the invention.