Vehicular forward-vision display system decreasing luminance with decreasing vehicle speed

A vehicular forward-vision display system includes a night-vision camera for scanning a nighttime image ahead of a vehicle and a head-up display for displaying the scanned nighttime image as a virtual image on a front windshield. Luminance of the displayed image is decreased with decreasing vehicle speed. The luminance of the nighttime image is thereby decreased under a low speed where vision aid is not so necessary. This decreasing of the luminance results in giving a driver relief from the bother of being caught by the scanned image displayed on the front windshield.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-219849 filed on Jul. 29, 2002.

1. Field of the Invention

The present invention relates to a vehicular forward-vision display system for scanning a nighttime image ahead of a vehicle and for displaying the scanned image as a virtual image on a front windshield. In particular, luminance of the displayed image is decreased with decreasing vehicle speed.

2.Backgroud of the Invention

At night, an image in a nighttime dark area cannot be visible by a naked eye of a driver in a long distance where headlights of a vehicle cannot reach (e.g., about 100 to 400 m ahead of a vehicle). This invisibility of the nighttime image may lead to a traffic accident.

A vehicular forward-vision display system is proposed in JP-A-H6-107036 for assisting safe driving by providing vision aid for nighttime vision of a driver. In the system, a hardly visible nighttime image is scanned by a night-vision camera and displayed as a virtual image on a windshield of a vehicle.

In the above system, when the scanned image is displayed on the windshield, luminance of the image is maintained in a predetermined amount without being varied. However, constantly maintaining the luminance of the displayed image results in exhibiting various problems.

At a low speed, the vision aid for displaying the images located in a long distance is unnecessary. The displayed image on the windshield therefore becomes an offending item for the driver when the luminance of the image is constantly maintained. In particular, during low-speed driving in a city, tail lamps of vehicles ahead are constantly displayed on the windshield.

While driving at a curve, the displayed image rapidly flows from side to side, which phenomenon lowers visibility and bothers the driver.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vehicular forward-vision display system where luminance of a displayed image is decreased when the displayed image becomes an offending item for a driver.

To achieve the above object, a vehicular forward-vision display system is provided with the following. A night-vision camera is disposed for scanning a nighttime image ahead of a vehicle. A displaying unit is disposed for displaying the scanned nighttime image as a virtual image on a front windshield. Here, luminance intensity of the displayed image is decreased with decreasing vehicle speed.

This structure enables the luminance intensity of the displayed nighttime image to be decreased and prevented from bothering the driver when the vehicle speed is too slow for the vision aid to be much required. In particular, this structure is effective when the vehicle travels around a curve naturally at a lowered speed. The displayed image that traverses from side to side is displayed on the windshield at lowered luminance intensity. This suppresses an offending image on the windshield.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicular forward-vision display system as a first embodiment of the present invention is directed to a passenger vehicle shown inFIG. 1. The system includes infrared lamps10for irradiating a nighttime image ahead of the vehicle by infrared light, a night-vision camera20for scanning the nighttime images irradiated by the infrared light, and a head-up display30as a displaying device for displaying the scanned images on a front windshield40of the vehicle.

The infrared lamps10irradiate near-infrared light having a range of wave length between 800 nm and 1000 nm and are disposed under headlights in front of the vehicle.

The night-vision camera20is a known infrared camera that has a telephoto lens21and scans an image by accumulating static electricity in proportion to received infrared. The infrared camera20is disposed near an upper side of the windshield40in an interior of the vehicle and in a rear side of a rearview mirror41as shown inFIG. 2.

The infrared camera20scans the forward vision of the vehicle through the front windshield40, and a signal of the scanned image is outputted to the head-up display30. A known composite video signal Vde is an instance of the signal of the scanned image.

The head-up display30includes a displaying unit D and an electronic control circuit E.

The displaying unit D is disposed in an instrument panel50that protrudes to the interior of the vehicle from a lower side of the windshield40. The displaying unit D includes a TFT type liquid crystal display (LCD) panel31and a backlight32. The LCD panel31is horizontally sustained in an opening51aof an upper wall51of the instrument panel50.

The LCD panel31receives a light from the backlight32and is activated to display a display image on a display window31a. The display image enters, as a display light, a combiner (not shown) provided in the windshield40. The combiner then reflects the display light, along a dotted line R inFIG. 2, to eyes of the driver M sitting in the driver's seat. A virtual image n is thereby formed ahead of the windshield40.

The backlight32is sustained in a rear side of the LCD panel31and powered by a backlight power33to turn on a light that enters the LCD panel31from a rear side of the LCD panel31. The displaying unit D activates the LCD panel31using a matrix drive circuit (not shown).

A shutter34(not shown) is disposed on an upper side of the LCD panel31. The shutter34is for preventing the LCD panel31from being deteriorated due to direct sunlight and is closed when the head-up display30is not used.

A manipulation panel60is disposed in an area where the driver can manipulate. The manipulation panel60includes a main switch61, a main-switch indicator62, an infrared-lamp indicator63, and a rheostat64.

The main switch61is manipulated by the driver for activating or ceasing the forward-vision system to output an ON-OFF signal to the electronic control circuit E. The main-switch indicator62is controlled for lighting up when the system is activated. The infrared-lamp indicator63is controlled for lighting up when the infrared lamps10light up. The rheostat64is manipulated by the driver for setting luminance of the displayed image to output, to the electronic control circuit E, a signal corresponding to the set luminance.

The electronic control circuit E receives: a vehicle speed signal detected by a vehicle speed sensor71; an ON-OFF signal from an ignition switch (IG SW)72; an ON-OFF sgnal from a head lamp relay73; a beam selection signal from a dimmer switch (DIM SW)74; and a day-night detection signal from a light control system75.

The head lamp relay73is disposed in a steering column and operated according to an ON-OFF state of the head lamp switch. The dimmer switch74is also disposed in the steering column and manipulated by the driver for selecting a low or high beam to output to the electronic control circuit E a low or high signal, respectively.

The light control system75is disposed on the upper wall51of the instrument panel50. It detects whether a predetermined light amount enters or not and outputs a detection signal to the electronic control circuit E.

The electronic control circuit E controls the forward-vision display system for starting when one of five signals is inputted. The five signals are as follows: (1) an ON signal from the ignition switch72; (2) an ON signal from the main switch61; (3) an ON signal from the head lamp relay73; (4) an ON signal from the dimmer switch74; and (5) a nighttime detection signal from the light control system75.

Long period irradiation of the infrared from the infrared lamp10may harm human's eyes. When the vehicle speed is lower than a certain speed, the infrared may relatively longer enter eyes of people ahead of the vehicle. The electronic control circuit E therefore controls the infrared lamp10for turning on only when the vehicle speed is not less than a predetermined speed in addition to the input of one of the above five signals. This thereby prevents the eyes of the people ahead of the vehicle from being harmed.

As explained above, when the forward-vision display system is activated, the forward nighttime image scanned by the infrared camera20is displayed as the virtual image on the windshield20by the head-up display30. At this moment, the electronic circuit E controls luminance intensity of the display image for being decreased with decreasing vehicle speed.

In detail, based on the inputted speed signal, an electric voltage applied to the backlight32from the backlight power33is controlled for the luminance intensity to be decreased with decreasing vehicle speed.

A micro-computer of the electronic control circuit E determines the luminance intensity according to the vehicle speed as shown inFIGS. 4 and 5.

At Step110, whether one of the above five signals is inputted, or whether the forward-vision system is activated is determined. When the forward-vision system is determined to be activated, whether the vehicle speed V is increasing is determined based on the inputted speed signal at Step120.

When the vehicle speed is determined to be increasing, whether the vehicle speed V is lower than a predetermined speed V1at Step130. When the vehicle speed V is determined to be lower than the predetermined speed V1(V<V1), the luminance intensity is determined to be set in the lowest value (MIN) at Step140. When the vehicle speed V is determined to be not lower than the predetermined speed V1(V≧V1), whether the luminance intensity is lower than the highest value (MAX) is determined at Step150. Here, the highest value is set through manipulation of the rheostat64. When the luminance intensity is determined to be lower than the highest value, the luminance intensity is determined based on the following formula 1 at Step160.
L=aV+b[Formula 1]

Here, L is luminance intensity, a and b are constant values.

By contrast, when the vehicle speed V is determined to be not increasing at Step120and when the vehicle speed V is determined to be decreasing at Step170, whether the vehicle speed V is lower than a predetermined speed V2at Step180. When the vehicle speed V is determined to be lower than the predetermined speed V2(V<V2), the luminance intensity is determined to be set in the lowest value at Step190. When the vehicle speed V is determined to be not lower than the predetermined speed V2(V≧V2), whether the luminance intensity is lower than the highest value is determined at Step200. When the luminance intensity is determined to be lower than the highest value, the luminance intensity is determined based on the following formula 2 at Step210.
L=cV+d[Formula 2]

Here, L is also luminance intensity, c and d are constant values.

When each determination at Steps110,150,170, and200is negated, processing is returned to be repeated. When the vehicle speed does not vary, determinations at Steps120and170are negated, so that the luminance intensity never varies.

Time chart of the luminance intensity according to the flowcharts shown inFIGS. 4 and 5as an instance is shown inFIG. 6. Here, the predetermined speed V1is 30 km/hour while the predetermined speed V2is 25 km/hour.

Namely, when the vehicle speed increases from 0 km/hour, the luminance intensity remains to be the lowest value until the vehicle speed reaches 30 km/hour and gradually increases to the highest value after the vehicle speed exceeds 30 km/hour. By contrast, when the vehicle speed decreases from greater than 30 km/hour, the luminance intensity remains to be the highest value until the vehicle speed reaches 25 km/hour and gradually decreases to the lowest value after the vehicle speed falls below 25 km/hour.

The vehicle to which the embodiment explained above is directed is supposed to be driven by the driver with the head lamp being turned on along a road at nighttime. Here, as the driver turns on the main switch61, the forward-vision system is activated and the infrared lamps10are turned on when the vehicle speed is higher than a predetermined speed. As the forward-vision system is activated, the main-switch indicator62turns on a light. As the infrared lamps10turn on the light, the infrared-lamp indicator63turns on the light.

The infrared irradiation from the infrared lamps10is reflected by a human or an object ahead of the vehicle, so that the reflection is received by the infrared camera20through the telephoto lens21. The human or the object is thereby scanned by the infrared camera20, which outputs the scanned image as a composite video signal Vde to the electronic control circuit E of the head-up display30.

The electronic control circuit E controls, based on the inputted video signal Vde, the matrix drive circuit that drives the LCD panel31. The electronic control circuit E controls the backlight power33for aiming at the luminance intensity determined based on the above flowchart.

The forward nighttime image scanned by the infrared camera20is projected as a display light on the windshield40by the LCD panel31. The virtual image m formed ahead of the windshield40is thereby recognized by the driver. The virtual image works as vision aid for the driver. This results in assisting safe driving.

According to the embodiment, when the vehicle speed is too low for the vision aid to be much required, the luminance intensity of the displayed nighttime image is decreased to be prevented from bothering the driver. In particular, this structure is effective when the vehicle travels around a curve naturally at a lowered speed. The displayed nighttime image that traverses from side to side is displayed on the windshield40at lowered luminance intensity for being prevented from giving an offending image to the driver.

In a second embodiment, the luminance intensity of the displayed image is stepwise varied by determining whether the vehicle speed is higher than a predetermined speed, while it is varied gradually according to the vehicle speed in the first embodiment. In detail, luminance intensity of the displayed image is determined as shown inFIGS. 7 and 8.

At Step120inFIG. 7, whether the vehicle speed is increasing is determined. When the vehicle speed is determined to be increasing, whether the vehicle speed is lower than a predetermined speed V3is determined at Step131. When the vehicle speed is determined to be lower than the predetermined speed V3(V<V3), the luminance intensity is determined to be the lowest value (MIN) at Step141. When the vehicle speed is determined to be not lower than the predetermined speed V3(V≧V3), the luminance intensity is determined to be the highest value (MAX) at Step161.

By contrast, when the vehicle speed is determined to be decreasing at Step170, whether the vehicle speed is lower than a predetermined speed V4is determined at Step181. When the vehicle speed is determined to be lower than the predetermined speed V4(V<V4), the luminance intensity is determined to be the lowest value at Step191. When the vehicle speed is determined to be not lower than the predetermined speed V4(V≧V4), the luminance intensity is determined to be the highest value at Step211.

Time chart of the luminance intensity according to the flowcharts shown inFIGS. 7 and 8as an instance is shown inFIG. 9. Here, the predetermined speeds V3and V4are 0 km/hour. Namely, when the vehicle speed is 0 km/hour, the luminance intensity is set to the lowest value. When the vehicle speed is more than 0 km/hour, the luminance intensity is set to the highest value.

Processing other than the determinations mentioned above in the second embodiment is similar to the processing in the first embodiment, so that a similar effect can be obtained.

The first and second embodiments can be modified below.

In the two embodiments, the infrared lamp10is used to irradiate and the night-vision camera20receives, from an object ahead of the vehicle, the reflected portion of the irradiation. However, without installing the infrared lamp10, the night-vision camera20can detect infrared that is naturally radiated from a creature or an object.

Although only one night-vision camera20is provided, two night-vision cameras20can be simultaneously provided to be used as a stereo camera for scanning ahead of the vehicle.

In the second embodiment, the predetermined speed V3for a case where the vehicle speed increases and the predetermined speed V4for a case where the vehicle speed decreases are set to the same value of 0 km/hour. However, the V3and V4can be, as matter of course, different values.