Vehicle headlights and vehicle headlight systems

Abstract

Vehicle headlight system (100), comprising: a headlight unit (20) capable of combining light beams from a plurality of light-emitting elements (28) to form a high beam distribution pattern; and a control unit (26) which controls switching on / off of each of the plurality of light-emitting elements (28), wherein the control unit (26) controls each light-emitting element (28) such that the luminance thereof is gradually reduced in a first duration when the luminance is reduced to a level at which the light-emitting element (28) is turned off, and controls each light-emitting element (28) such that the luminance thereof is gradually reduced in a second duration which is longer than the first duration when the luminance is reduced to a level at which the light-emitting element (28) remains turned on at the reduced luminance.

Description

[0001] The present invention relates to vehicle headlights and vehicle headlight systems used in motor vehicles or the like.

[0002] Typically, a vehicle headlight can switch between a low beam and a high beam. The low beam illuminates a nearby area with a predetermined illuminance. The light distribution patterns of the low beam are controlled so as not to cause glare for oncoming vehicles or vehicles ahead, and the low beam is primarily used when the vehicle is traveling in an urban area. Meanwhile, the high beam illuminates a distant, wide area ahead with a relatively high illuminance and is primarily used when the vehicle is traveling at high speed on a road with few oncoming vehicles or few vehicles ahead.Accordingly, the high beam provides better visibility for the driver than the low beam, but disadvantageously it causes glare for a driver of a preceding vehicle or an oncoming vehicle or for a pedestrian.

[0003] In recent years, a technique for dynamically and adaptively controlling a high beam distribution pattern based on a vehicle's environmental conditions has been proposed (see, for example, JP 2008-137516 A). According to this technique, the presence of a preceding vehicle, an oncoming vehicle, or a pedestrian is detected, and light in an area corresponding to the detected vehicle or pedestrian is attenuated, thus reducing glare to the vehicle or pedestrian.

[0004] Typically, in a conventional vehicle headlight system, the luminance is randomly reduced gradually to a target luminance over the same period of time, whether reducing the luminance to a level where the headlight remains on at reduced luminance or to a level where the headlight is off, to reduce glare to a vehicle or pedestrian. This may be preferable in terms of simplifying control, but it leaves room for improvement in terms of driver comfort.

[0005] The present invention has been made in view of such a situation and aims to provide a vehicle headlight system that can improve the comfort of a driver.

[0006] To solve the above-described problem, a vehicle headlight system according to one aspect of the present invention includes a headlight unit that can combine light beams from a plurality of light-emitting elements to form a high beam distribution pattern, and a control unit that controls the on / off state of each of the plurality of light-emitting elements. The control unit controls each light-emitting element such that the luminance thereof is gradually reduced in a first period when the luminance is reduced to a level at which the light-emitting element is turned off, and controls each light-emitting element such that the luminance thereof is gradually reduced in a second period longer than the first period when the luminance is reduced to a level at which the light-emitting element remains turned on with the luminance reduced.

[0007] Embodiments will now be described by way of example only with reference to the accompanying drawings, which are given as non-limiting examples and in which like elements are numbered alike in several figures, and in which: is Fig. 1 is a block diagram of a vehicle headlight system according to an embodiment; illustrated Fig. 2 schematically shows a light distribution pattern formed by the vehicle headlight system; illustrate Fig. 3A to 3H show an example of a change in the luminance distribution of each sub-area of ​​a high beam distribution pattern; is Fig. 4 is a timing diagram illustrating a change in the luminance of each sub-area with time; illustrate Fig. 5A and Fig. 5B shows another example of a change in the luminance distribution of each sub-area of ​​a high beam distribution pattern; and is Fig. 6 is a timing chart according to a comparative example illustrating a change in luminance of each sub-area of ​​a high beam distribution pattern formed by a vehicle headlight system with time.

[0008] The invention will now be described by reference to the preferred embodiments. This is not intended to limit the scope of the present invention, but rather to illustrate the invention by way of example. The size of the components in each figure may be changed to aid understanding. Some of the components in each figure may be omitted if they are not important to the explanation.

[0009] Fig. 1 is a block diagram of a vehicle headlight system 100 according to one embodiment. The vehicle headlight system 100 includes a vehicle speed sensor 10, a steering angle sensor 12, a camera 14, a vehicle control unit 16, and a vehicle headlight 18.

[0010] The vehicle speed sensor 10 detects the rotational speed of the wheels to determine the vehicle's speed. The steering angle sensor 12 detects the steering angle of the steering wheel. The camera 14 captures an image of an area in front of the vehicle.

[0011] The vehicle control unit 16 controls the vehicle as a whole. The vehicle control unit 16 detects the presence of a preceding vehicle or an oncoming vehicle and the position of the detected vehicle based on the image information obtained from the camera 14. Based on this detection result, the vehicle speed information, and the steering angle information, the vehicle control unit 16 determines a light distribution pattern formed by a combination of an on area to be illuminated with a light beam and an off area (blocked area) not to be illuminated with a light beam. The vehicle control unit 16 transmits a pattern instruction S1 indicating the determined light distribution pattern to the vehicle headlight 18.

[0012] The vehicle headlight 18 forms a high beam distribution pattern. The actual vehicle headlight 18 is equipped with an additional high beam for illuminating a more distant area, a low beam, a clearance lamp, and so on, in addition to a high beam, but these are omitted here.

[0013] The vehicle headlight 18 includes a headlight unit 20, a semiconductor switch 22, a lighting circuit 24, and a headlight control unit 26. The actual vehicle headlight system 100 is provided by a pair of right and left vehicle headlights 18, but only one of the two is shown here.

[0014] The headlight unit 20 contains several semiconductor light sources (e.g., LEDs) 28, which can be individually switched on / off. Each LED 28 is switched on when a control current I LD turned on.

[0015] The semiconductor switch 22 is provided on a path through which power is supplied from a battery (not shown) to the lighting circuit 24, and the switching on / off of the semiconductor switch 22 is controlled in accordance with a control signal S2 from the headlight control unit 26. The semiconductor switch 22 is turned on when the LEDs 28 are turned on.

[0016] The headlight control unit 26 controls the turning on / off of the plurality of LEDs 28 individually based on the pattern instruction S1. In the present embodiment, the headlight control unit 26 selects, for each of the plurality of LEDs 28, one of a first mode, a second mode, and a third mode in which the luminance is to be changed stepwise, and generates an on / off instruction signal S3 instructing each LED 28 to turn on or off in the selected mode.

[0017] The headlight control unit 26 selects the first mode when an LED 28 is to be turned off. In the first mode, the luminance is gradually reduced so that the luminance reaches a level at which the LED 28 is turned off (i.e., the luminance is 0) in a first duration (i.e., the LED 28 is turned off gradually). In one example, the first duration is 300 ms. When the vehicle is traveling at high speed, the first duration may be 500 ms. This can prevent a situation in which reflection plates are confused with a vehicle ahead and the luminance is frequently changed.

[0018] The headlight control unit 26 selects the second mode when an LED 28 is to remain illuminated at reduced luminance. In the second mode, the luminance is gradually reduced so that the luminance reaches the target luminance at which the LED 28 remains illuminated at reduced luminance for a second duration longer than the first duration. In one example, the second duration is 400 ms. If the vehicle is traveling at high speed, the second duration may be 7000 ms for the same reason as described above.

[0019] The headlight control unit 26 selects the third mode when an LED 28 is to remain illuminated at an increased luminance. In the third mode, the luminance is gradually increased from a level at which the LED 28 is off or on to a target luminance at which the LED 28 is illuminated at an increased luminance for the second duration, as in the second mode.

[0020] The lighting circuit 24 includes drive circuits 30 and step change controllers 32 provided for the respective LEDs 28. The drive circuits 30 provide drive currents I LD , corresponding to the respective light control signals S4, to the LEDs 28. Each control circuit 30 can perform both analog light control by adjusting the amount of the control current I LD as well as pulse width modulation (PWM) light control by varying the duty cycle of the control current I LDby controlling the control current I LD switched at high speed, or can only perform one of the two.

[0021] Each step change controller 32 generates a light control signal S4 that changes stepwise with time in accordance with an on / off instruction signal S3 from the headlight control unit 26. Specifically, when the first mode is selected, the step change controller 32 causes the light control signal S4 to change relatively steeply in a direction in which the drive current I LD decreases. When the second mode is selected, the step change controller 32 causes the light control signal S4 to change gradually over time in a direction in which the drive current I LDdecreases. When the third mode is selected, the step change controller 32 causes the light control signal S4 to change gradually over time in a direction in which the drive current I LD increases.

[0022] Fig. 2 schematically illustrates a light distribution pattern formed by the vehicle headlight system 100 configured as described above. Fig. Figure 2 illustrates a light distribution pattern formed on a virtual vertical screen arranged at a predetermined position in front of the headlight, for example, at a position 25 meters in front of the headlight.

[0023] A light distribution pattern PH is a high beam distribution pattern formed by illumination light from the headlight unit 20. The light distribution pattern PH is divided into a plurality of (eight) sub-areas PHa to PHh, and the sub-areas correspond to the respective LEDs 28. In other words, the vehicle headlight 18 can form the high beam distribution pattern PH in a region ahead of the vehicle, which is composed of the plurality of sub-areas PHa to PHh corresponding to the illumination areas of the respective LEDs 28.

[0024] Fig. 3A to 3H illustrate an example of a change in the luminance distribution of each of the sub-areas PHa to PHh. Fig. 3A to 3H illustrate the luminance distribution at times T0 to T7, respectively. The longer a given bar in Fig. 3A to 3H, the higher the luminance of its corresponding sub-area. In other words, the longer a given bar, the higher the luminance of LED 28 illuminating the corresponding sub-area. Fig. Figure 4 is a timing diagram showing changes in the luminance of the sub-areas PHb to PHf under the conditions Fig. 3A to 3H, or, in other words, changes in the luminance of the LEDs 28 illuminating the respective partial areas PHb to PHf over time. An exemplary case will be described below. Specifically, at time T1, a target light distribution pattern is changed, a preceding vehicle is detected in the partial areas PHc to PHf, and the partial areas PHc to PHf are set as blocked areas. At time T2, the detection of the preceding vehicle ends in the partial areas PHe and PHf, and the partial areas PHe and PHf are set as on-areas. At time T3, the detection of the preceding vehicle ends in the partial area PHd, and the partial area PHd is set as an on-area.

[0025] The luminance of the partial areas PHa and PHb is gradually reduced to a level at which the LEDs 28 are turned off because the target light distribution pattern has changed at time T1. In addition, the luminance of the partial area PHc is gradually reduced to a level at which the LED 28 is turned off because the partial area PHc has been set as a blocked area at time T1. In other words, the luminance of the LEDs 28 corresponding to the respective partial areas PHa to PHc is gradually reduced in the first mode (ie, the LEDs 28 are turned off in a first period t1).

[0026] The luminance of the partial area PHd begins to be gradually reduced to a level at which the LED 28 is turned off because the partial area PHd has been set as a blocked area at time T1. In other words, the luminance of the LED 28 corresponding to the partial area PHd begins to be gradually reduced in the first mode (i.e., the LED 28 begins to be gradually turned off in the first duration t1). Since the partial area PHd has been set as an on-area at time T3, the luminance of the partial area PHd is then gradually reduced to a level at which the LED 28 is turned on at a luminance corresponding to the target light distribution pattern. In other words, the luminance of the LED 28 corresponding to the partial area PHd is gradually reduced to the target luminance in the second mode (i.e., the luminance is gradually reduced in a second duration t2).

[0027] The luminance of the partial area PHe begins to be gradually reduced to a level at which the LED 28 is turned off because the partial area PHe has been set as a blocked area at time T1. In other words, the luminance of the LED 28 corresponding to the partial area PHe begins to be gradually reduced in the first mode. Since the partial area PHe has been set as an on area at time T2, the luminance of the partial area PHe is then gradually reduced to a level at which the LED 28 is turned on at a luminance corresponding to the target light distribution pattern. In other words, the luminance of the LED 28 corresponding to the partial area PHe is gradually reduced to a target luminance in the second mode.

[0028] The luminance of the partial area PHf begins to be gradually decreased to a level at which the LED 28 is turned off because the partial area PHf has been set as a blocked area at time T1. In other words, the luminance of the LED 28 corresponding to the partial area PHf begins to be gradually decreased in the first mode. Since the partial area PHf has been set as an on area at time T2, the luminance of the partial area PHf is then gradually increased to a level at which the LED is turned on at a luminance corresponding to the target light distribution pattern. In other words, the luminance of the LED 28 corresponding to the partial area PHf is gradually increased to the target luminance in the third mode (i.e., the luminance is gradually increased in the second period t2).

[0029] The luminance of the partial areas PHg and PHh is gradually reduced to a level where the LEDs 28 are illuminated at a luminance corresponding to the target light distribution pattern, since the target light distribution pattern has been changed at time T1. In other words, the luminance of the LEDs 28 corresponding to the partial areas PHg and PHh is gradually reduced in the second mode.

[0030] As can be clearly seen from the timing diagrams for the sub-areas PHc and PHg, the luminance is changed gradually in the first mode (i.e., in a relatively short duration) when an LED 28 is to be gradually turned off, and the luminance is changed gradually in the second mode (i.e., in a relatively long duration) when an LED 28 is to remain turned on at reduced luminance. In addition, as can be clearly seen from the timing diagrams for the sub-areas PHe and PHf, the luminance is changed gradually in the same duration when the luminance is to be changed to a level at which the LED 28 is turned on, regardless of whether the luminance is decreased or increased.In addition, as can be clearly seen from the timing diagrams for the sub-ranges PHd to PHf, if the luminance is to be changed to a level at which an LED 28 is switched on, such a change in luminance ends in the order in which the change started.

[0031] Fig. 5A and Fig. 5B illustrate another example of a change in the luminance distribution of each of the sub-regions PHa to PHh of the light distribution pattern PH. This example illustrates a case where the light distribution pattern differs from that shown in Fig. 5A illustrated state to that in Fig. 5B, when all LEDs 28 are off. The luminance of all the sub-areas PHa to PHh is gradually reduced to a level at which the LEDs 28 are off. That is, the luminance of the LEDs 28 corresponding to the respective sub-areas PHa and PHh is gradually reduced in the first mode. In other words, the luminance of all the sub-areas becomes 0 in the first period (i.e., at substantially the same timing).

[0032] Fig. 6 is a timing chart illustrating an example of changes with time in the luminance of partial areas PHa to PHh of a high beam distribution pattern PH formed by a vehicle headlight system according to a comparative example for comparison with the vehicle headlight system 100, or, in other words, changes with time in the luminance of LEDs illuminating the respective partial areas PHb to PHf. Fig. 6 corresponds to Fig. 4. In the vehicle headlight system according to the comparative example, the luminance is gradually reduced in a first duration t1, regardless of whether an LED is to be gradually turned off or the luminance of an LED is to be gradually reduced to a level at which the LED remains on with reduced luminance. Meanwhile, the luminance is gradually increased in a second duration t2 if the luminance is to be gradually increased to a level at which the LED remains on with increased luminance.

[0033] As can be clearly seen from the timing charts for the partial areas PHb and PHf, in the vehicle headlight system according to the comparative example, when the luminance of an LED is to be decreased to a level at which the LED remains on, the luminance is gradually decreased in a relatively short period of time, as in the case where the luminance of an LED is gradually decreased to a level at which the LED is off. Therefore, the brightness in an area in front of the vehicle changes rapidly. In addition, as can be clearly seen from the timing charts for the partial areas PHc to PHe, when the luminance is to be changed to a level at which the LED is turned on, the luminance in the vehicle headlight system according to the comparative example is changed in different durations for increasing the luminance and for decreasing the luminance to achieve the target luminance.Specifically, the luminance is gradually changed in a relatively short period of time when the luminance is decreased, and the luminance is gradually changed in a relatively long period of time when the luminance is increased. Therefore, the gradual decrease in the luminance of the sub-area PHc, which started later, ends before the gradual increase in the luminance of the sub-area PHe, which started earlier.

[0034] Hereinafter, advantageous effects of the vehicle headlight system 100 according to the embodiment will be described in view of the foregoing. With the vehicle headlight system 100 according to the embodiment, the headlight control unit 26 selects the first mode when the luminance of an LED 28 is to be gradually reduced to a level at which the LED 28 is turned off (i.e., the LED 28 is gradually turned off). Meanwhile, the headlight control unit 26 selects the second mode when the luminance of an LED 28 is to be gradually reduced to a level at which the LED 28 remains turned on with the luminance reduced. In other words, although the luminance is reduced in both cases, the luminance is gradually changed in a relatively short period of time when an LED 28 is turned off.Accordingly, glare for a driver of a preceding vehicle or an oncoming vehicle, or for a pedestrian, can be suppressed. On the other hand, when the luminance is gradually reduced to a level at which the LED 28 remains lit, the luminance is gradually changed over a relatively long period of time, and accordingly, a rapid change in brightness in an area in front of the vehicle, as in the case of the comparative example, can be prevented. Accordingly, driver comfort can be improved.

[0035] Furthermore, with the vehicle headlight system 100 according to the embodiment, when the luminance of an LED 28 is to be increased to a level at which the LED 28 remains lit with increased luminance, the headlight control unit 26 increases the luminance in a duration substantially the same as in the case where the luminance of an LED 28 is decreased to a level at which the LED 28 remains lit with reduced luminance. In other words, when the luminance is changed to a level at which an LED 28 remains lit with increased luminance, the luminance is gradually changed to reach the target luminance in substantially the same duration whether the luminance is increased or decreased.Accordingly, a feeling of discomfort that a driver may have when the luminance is gradually changed to reach the target luminance in different time periods as in the comparative example can be suppressed.

[0036] So far, the present invention has been described based on one embodiment. However, this embodiment is merely illustrative, and it will be understood by those skilled in the art that various modifications can be made to the combinations of components and processing methods of the embodiment, and that such modifications also fall within the scope of the present invention. Such modifications will be described below. First modification

[0037] In the embodiment, a case has been described where the luminance is controlled to achieve a target luminance in the second duration when the luminance is changed to a level at which the LED is turned on. Alternatively, when the luminance is changed to a level at which an LED is turned on while the vehicle is traveling along a curve (that is, when the steering angle is equal to or greater than a predetermined value), the luminance may be controlled to achieve the target luminance in a third duration that is longer than the first duration and equal to or shorter than the second duration. While the vehicle is traveling along a curve, the third duration may be 200 ms in one example, and the second duration may be 200 ms. In other words, the luminance may be controlled to achieve the target luminance in a relatively short duration while the vehicle is traveling along a curve.In this case, the direction of travel can be illuminated more quickly.

[0038] The present invention has been described on the basis of embodiments with the use of specific terms, but the embodiments merely illustrate the principle and applications of the present invention, and a number of modifications of the embodiments and changes in the arrangement can be made within a scope that does not deviate from the spirit of the present invention set forth in the claims.

[0039] A vehicle headlight system according to one aspect of the present invention includes a headlight unit capable of combining light beams from a plurality of light-emitting elements to form a high-beam distribution pattern, and a control unit that controls the turning on / off of each of the plurality of light-emitting elements. The control unit controls each light-emitting element such that the luminance thereof is gradually reduced in a first period when the luminance is reduced to a level at which the light-emitting element is turned off, and controls each light-emitting element such that the luminance thereof is gradually reduced in a second period longer than the first period when the luminance is reduced to a level at which the light-emitting element remains turned on with the reduced luminance.

[0040] Although the luminance is gradually reduced in both cases when the luminance is reduced to a level at which the light-emitting element remains turned on with the luminance reduced, according to this aspect, the luminance is gradually reduced in a longer period of time than in the case where the luminance is reduced to a level at which the light-emitting element is turned off.

[0041] The vehicle headlight system may further include a detection unit that detects a preceding vehicle. When the detection unit has detected a preceding vehicle, the control unit may control a light-emitting element among the plurality of light-emitting elements that illuminates the preceding vehicle such that the luminance thereof is gradually reduced to a level at which the light-emitting element is off in the first period. Accordingly, when the luminance is reduced to a level at which the light-emitting element is off upon detection of the preceding vehicle, the luminance is gradually reduced in a shorter period of time than in a case where the luminance is reduced to a level at which the light-emitting element remains on with the reduced luminance.

[0042] When the luminance of each light-emitting element is increased to a level at which the light-emitting element is on at the increased luminance, the control unit can gradually increase the luminance in a duration substantially the same as the second duration. In this case, when the luminance is changed to a level at which the light-emitting element is on, the luminance is gradually changed in substantially the same duration, regardless of whether the luminance is increased or decreased.

[0043] When the luminance of each light-emitting element is changed to a predetermined level at which the light-emitting element is turned on while the vehicle is traveling along a curve, the control unit may change the luminance stepwise in a third duration that is longer than the first duration and shorter than or substantially equal to the second duration. In this case, the luminance is changed stepwise in a relatively short period of time while the vehicle is traveling along a curve, even if the luminance is to be changed to a level at which the light-emitting element is turned on.

[0044] Another aspect of the present invention provides a vehicle headlight. This vehicle headlight includes a headlight unit capable of combining light beams from a plurality of light-emitting elements to form a high-beam distribution pattern, and a drive circuit that turns the plurality of light-emitting elements on / off in response to a control signal that controls the turning on / off of each of the plurality of light-emitting elements.Based on the control signal, the drive circuit controls each light-emitting element such that the luminance thereof is gradually reduced in a first duration when the luminance is reduced to a level at which the light-emitting element is turned off, and controls each light-emitting element such that the luminance thereof is gradually reduced in a second duration longer than the first duration when the luminance is reduced to a level at which the light-emitting element remains turned on at the reduced luminance.

[0045] According to this aspect, when the luminance is reduced to a level at which the light-emitting element remains turned on with the luminance reduced, the luminance is gradually reduced in a longer period of time than in the case where the luminance is reduced to a level at which the light-emitting element is turned off, although the luminance is gradually reduced in both cases.

Claims

[1] A vehicle headlight system (100) comprising: a headlight unit (20) capable of combining light beams from a plurality of light-emitting elements (28) to form a high beam distribution pattern; and a control unit (26) which controls switching on / off of each of the plurality of light-emitting elements (28), wherein the control unit (26) controls each light-emitting element (28) such that the luminance thereof is gradually reduced in a first duration when the luminance is reduced to a level at which the light-emitting element (28) is turned off, and controls each light-emitting element (28) such that the luminance thereof is gradually reduced in a second duration which is longer than the first duration when the luminance is reduced to a level at which the light-emitting element (28) remains turned on at the reduced luminance. [2] The vehicle headlight system (100) of claim 1, further comprising: a detection unit (16) which detects a vehicle in front, wherein the control unit (26), when the detection unit (16) has detected a preceding vehicle, controls a light-emitting element (28) among the plurality of light-emitting elements (28) that illuminates the preceding vehicle so that the luminance thereof is gradually reduced to a level at which the light-emitting element (28) is turned off in the first duration. [3] The vehicle headlight system (100) according to claim 1 or 2, wherein the control unit (26) increases the luminance stepwise in a duration substantially the same as the second duration when the luminance of each light-emitting element (28) is increased to a level at which the light-emitting element (28) is turned on at the increased luminance. [4] The vehicle headlight system (100) according to any one of claims 1 to 3, wherein the control unit (26) changes the luminance stepwise in a third duration longer than the first duration and shorter than or substantially equal to the second duration when the luminance of each light-emitting element (28) is changed to a predetermined level at which the light-emitting element (28) is turned on while the vehicle is traveling along a curve. [5] Vehicle headlight (18), comprising: a headlight unit (20) capable of combining light beams from a plurality of light-emitting elements (28) to form a high beam distribution pattern; and a drive circuit (30) that switches the plurality of light-emitting elements (28) on / off in response to a control signal that controls the switching on / off of each of the plurality of light-emitting elements (28), wherein the drive circuit (30) controls each light-emitting element (28) based on the control signal such that the luminance thereof is gradually reduced in a first duration when the luminance is reduced to a level at which the light-emitting element (28) is turned off, and controls each light-emitting element (28) such that the luminance thereof is gradually reduced in a second duration longer than the first duration when the luminance is reduced to a level at which the light-emitting element (28) remains turned on with the luminance reduced.

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