Apparatus for Displaying Images for Vehicles

(1) Field of the Invention

The present invention relates to an apparatus for displaying images which controls a color hue of an image appearing on a screen of a cathode ray tube of a video equipment installed in a vehicle when a visual angle controlling filter such as a liquid crystal panel is installed in a front space of the screen of the CRT (Cathode Ray Tube) and a voltage is applied to the visual angle controlling filter.

(2) Background of the art

In a previously proposed image displaying apparatus, a louver type filter is disposed in front of a CRT (Cathode Ray Tube) so that a visible angle is limited to directions except a particular direction in order to prevent the images displayed on a screen of the CRT from viewing from a vehicular driver's seat during a drive of the vehicle in order to assure a safety driving.

When the vehicle runs, the louver type filter is mounted by a viewer in a front end of the CRT so that louvers in the filter cause a light directed to the driver's seat to be interrupted. However, since the louvers are designed so that the light toward passenger's seats except the driver's seat is not interrupted, thus the images on the CRT can be viewed from each of the passenger's seats.

In addition, when the vehicle stops and parks, the images on the CRT can be viewed from all vehicular seats including the driver's seat.

In another previously proposed image displaying apparatus, a liquid crystal panel is used as a visual angle controlling filter in place of the louver type filter since the louver type filter is inconvenient in its troublesome mounting and removal operations.

Controlling means applies a voltage to the liquid crystal panel during the run of the vehicle. The light from the CRT toward the driver's seat is thus interrupted. On the other hand, the light toward the passenger's seats except the driver's seat is not interrupted so as to enable viewing of the CRT from the passenger's seats. During the stop of the vehicle, the voltage is not applied to the liquid crystal panel so that the images on the screen of the CRT can be viewed from all directions.

However, since, in the latter previously proposed displaying apparatus, the liquid crystal panel has different light transmission factors according to a wavelength of the incident light during the application of voltage with the vehicle run, a color hue of the image on the screen of the CRT as viewed through the liquid crystal panel is varied so that the images on the screen of the CRT cannot clearly and correctly be viewed.

In addition, when the voltage application to the liquid crystal panel is turned off with the vehicle stopped, or vice versa (when the application is turned on with the vehicle started), the color hue is varied so that each viewer gives an unpleasant feeling.

It is an object of the present invention to provide an apparatus for displaying images on a screen of a video equipment applicable to vehicles in which the color hue of the image viewed through such a visual angle controlling filter is not varied even when the visual angle controlling filter is operated.

The above-described object can be achieved by providing an apparatus for displaying an image on a screen of a video equipment applicable to a vehicle, comprising: (a) a visual angle controlling filter for limiting a visual recognition area for the image appearing on the screen so that a light of the image on the screen directed toward a driver's seat of the vehicle is interrupted in response to an application of a voltage; (b) first means for detecting the vehicle run; (c) second means for controlling the application of voltage according to the result of detection that the vehicle run; (d) third means for detecting the application of voltage to the visual angle controlling filter; and (e) fourth means for controlling a color hue of the image on the screen in response to the detection result of the third means that the voltage is applied to the visual angle controlling filter.

The above-described object can also be achieved by providing an apparatus comprising: (a) a visual angle controlling filter located in front of a screen of a video equipment, the visual angle controlling filter being capable of viewing an image appearing on the screen of the video equipment therethrough in directions except a particular direction in response to an application of predetermined interrupting means thereto; (b) first means for detecting a condition of the application of the predetermined interrupting means; (c) second means for controlling the application of the predetermined interrupting means according to the result of the detection of the condition; (d) third means for detecting whether the predetermined interrupting means is applied to the visual angle controlling filter; (e) fourth means for controlling a color hue of the image appearing on the screen of the video equipment in response to the result of detection by the third means so that the color hue of the image on the screen as viewed through the visual angle controlling filter does not change irrespective of the application of the predetermined interrupting means.

FIG. 1 is a schematic circuit block diagram in a first preferred embodiment of an image displaying apparatus according to the present invention.

FIG. 2 is a schematic circuit wiring diagram of a color hue controlling circuit shown in FIG. 1.

FIG. 3 is a schematic circuit block diagram of an alternative of the color hue controlling circuit using a microcomputer.

FIG. 4 is an operational flowchart of a routine executed by the microcomputer shown in FIG. 3.

FIGS. 5 and 6 are schematic circuit block diagram of variations of a light emitting element shown in FIGS. 1 and 2.

FIG. 7 is a schematic circuit block diagram of a second preferred embodiment of the image displaying apparatus according to the present invention.

Reference will hereinafter be made to the drawings in order to facilitate understanding of the present invention.

FIG. 1 shows a first preferred embodiment of an image displaying apparatus according to the present invention.

A liquid crystal panel 12 is disposed along a front screen of a CRT (Cathode Ray Tube) 11 so as to enclose the screen of the CRT. The CRT 11 is mounted in a vehicle body.

A vehicle speed detector 13 is installed in the vehicle for detecting a run state or stopped state of the vehicle. The speed detector 13 may, e.g., be a vehicle speedometer.

An oscillator 14 is connected between the speed detector 13 and liquid crystal panel 12 for controlling the visual angle controlling filter 12 in response to an output signal of the speed detector 13 indicating that the vehicle runs.

A light emitting element (electro-luminescent element) 15 is disposed in the vicinity of an edge of the liquid crystal panel 12 for detecting an operation of the liquid crystal panel 12.

It is noted that a photo diode 16 of a white balancer is disposed in an opposite side of the light emitting diode 16 with respect to the edge of the liquid crystal panel 12. The photo diode 16 is used to detect the color hue of the liquid crystal panel 12 and to adjust the color hue thereof.

In addition, a color hue controlling circuit 17 which operates in accordance with an information derived from the photo diode 16. The color hue controlling circuit 17 is connected to a CRT drive circuit 18.

The detailed structures of the photo diode 16 and color hue controlling circuit 17 are exemplified by FIG. 2.

The photo diode 16 shown in FIGS. 1 and 2 includes an element 16a for a blue level and another element 16b for a red level, both elements being disposed and wired in parallel to each other. Output voltages V.sub.1 and V.sub.2 of both elements 16a, 16b are supplied to both input terminals of a first operational amplifier 25 of the color hue controlling circuit 17.

The color hue controlling circuit 17 includes the first operational amplifier 25 and second operational amplifier 26, a variable resistor 27, and a plurality of resistors R.sub.11 to R.sub.16. An output terminal of the second operational amplifier 26 is connected to the CRT drive circuit 18.

When the vehicle stops, the vehicle speed detector 13 does not output the signal and the voltage is not applied to the liquid crystal panel 12. Therefore, the liquid crystal panel is transparent. The screen i.e., the images on the screen can be viewed from any direction of a front passenger's seat 21, rear passenger's seat 22, and driver's seat 20 of the vehicle.

During the vehicle run, the speed detector 13 is operated, the oscillator 14 is driven, and liquid crystal panel driving oscillator 14 is driven. Consequently, the voltage is applied to the liquid crystal panel 12. At this time, the direction toward an arrow marked direction A becomes discolored (in black). Therefore, the light from the screen of the CRT 11 toward the driver's seat 20 is interrupted so that the driver cannot view the screen of the CRT 11. Although the screen of the CRT 11 can be viewed from the front passenger's seat 21 and rear passenger's seat 22, the images on the screen of the CRT 11 viewed through the liquid crystal panel 12 to which the voltage is applied becomes blue since the light transmission characteristic becomes different according to a wavelength of the incident light.

To compensate such color hue, the following operation is carried out in the first preferred embodiment.

When the liquid crystal panel is operated, the light from the light emitting element 15 is transmitted through the liquid crystal panel 13 and irradiates the blue level element 16a and red level element 16b of the photo diode 16. At this time, a voltage output V.sub.1 of the blue level element 16a and a voltage output V.sub.2 of the red level element 16b are subtracted by means of the first operational amplifier 25 forming the hue controlling circuit 17. The output voltage of the first operational amplifier e.sub.2 can be expressed as follows:

The output voltage e.sub.2 of the first operational amplifier 25 is changed to e.sub.3 by means of a voltage e.sub.1 of the variable resistor 27 and the first operational amplifier 26. The voltage e.sub.3 is inputted into the CRT drive circuit 18 to control the color hue of the CRT 11.

FIG. 3 shows a variation of the color hue control circuit 17 in which a microcomputer 28 is used in place of an analog circuit 17 using the operational amplifiers shown in FIG. 2.

A digital-to-analog converter 29 is connected between an I/O port of the microcomputer 28 and the CRT controller 18.

FIG. 4 shows an operational flowchart executed by means of the microcomputer 28.

In a step S.sub.1, a CPU in the microcomputer 28 clears all memories.

In a step S.sub.2, the CPU inputs signals indicating that the blue level element 16a and red level element 16b receive the lights transmitted through the liquid crystal panel 12.

In a step S.sub.3, the CPU derives a difference between the blue level signal A and the red level signal B and converts the difference into the color tone value C (C=D.times.(A-B)).

Next, the CPU reads the external color tone signal E and color signal F in steps S.sub.4 and S.sub.5. Then, the CPU determines the levels of the color tone and color (G and H) in a step S.sub.6. Then, the CPU outputs the color tone level G and color level H to the CRT controller 18 in a step S.sub.7.

FIGS. 5 and 6 show variations of the white light emitting element 15 shown in FIG. 1.

In FIGS. 5 and 6, an end portion of the screen of the CRT 31 is formed with a superimpose (discoloring of white) portion 33. The light from the superimpose portion 33 is transmitted through the liquid crystal panel 12 and is received by the photo diode 35.

It is noted that, as shown in FIG. 6, a light reflecting film 36 is disposed on a part of the panel 12 so as to render the film 36 reflect the light from the superimpose portion 33 of the CRT screen to cause the light twice to transmit through the panel 12. Then, the photo diode 37 receives the light.

FIG. 7 shows a second preferred embodiment of the image displaying apparatus according to the present invention.

In FIG. 7, the liquid crystal panel 42 is disposed in a front space of the CRT screen 41.

The signal derived from the speed detector 43 causes the liquid crystal panel driving oscillator 44 to apply the voltage to the panel 41 to limit a visual recognition area in a direction to the driver's seat. A transistor circuit 45 provides means for driving the oscillator 44 in response to the signal derived from the speed detector 43.

Since the drive of the transistor circuit 45 means the operation of the liquid crystal panel 41, a signal from the transistor 45 causes a relay A contact (analog switch) 46 to be driven so that the relay contact A turns on or off a variable resistor 47. The color hue controlling circuit includes another operational amplifier 49 whose input terminals receive the voltage derived from an external variable resistor 48 for adjusting the color hue and the voltage of the DC level adjusting variable resistor 47. The output terminal of the other operational amplifier 49 is connected to an input terminal of the CRT controller 50.

When the vehicle stops, the vehicle speed detector 43 is not operated and the liquid crystal panel 52 becomes transparent. Then, when the vehicle runs and the speed detector 43 is operated, the oscillator 44 is driven through the transistor 45 so that the liquid crystal panel 42 becomes partially black. At this time, since the light transmitted through the panel 42 becomes blue due to the different transmission characteristic of the panel 42 according to the wavelength. Therefore, the relay contact A 46 is operated in response to the transistor 45. The voltage across the DC level variable resistor 47 is inputted to the other operational amplifier 49 together with the voltage of the color hue adjusting variable resistor 48. The voltage determined by the two variable resistors 47 and 48 is applied to the input terminal of the CRT controller 50 so that the images of the CRT 41 as viewed through the liquid crystal panel 42 are the same as those when the panel 42 is not operated. During the vehicle stop, the contact of the relay 46 is grounded so that the color hue is returned to that determined by the external variable resistor 48 and the liquid crystal panel 42 becomes transparent. The color hue of the CRT 11 is changed by a voltage set by means of the DC level adjusting variable resistor 47 during the vehicle run. Therefore, the color hue change due to the operation of the panel 42 is thus corrected.

It is noted that it is desirable for the speed detector to have a limit speed value for determining that the vehicle has run, the limit speed value being such that the vehicle has run even if the vehicle speed is very slow. For example, the speed detector comprises a sensor for detecting a pulse signal in proportion to the vehicle speed and has a time delay such that the sensor determines that the vehicle stops when the subsequent pulse signal is not detected after a lapse of a predetermined period of time of the detection of the pulse signal. The sensor is set so that the vehicle runs as the vehicle speed in very low even though a more time has taken upon the detection of the pulse signal with the predetermined period of time set as a long duration.

In the way described above, since the speed detector determines that the vehicle has run for a constant period of time upon the actual stop in a case where the vehicle run and stop are frequently repeated, no repetition of the operation and non-operation of the liquid crystal panel cannot be carried out.

As described hereinabove, in the image displaying apparatus according to the present invention, the voltage is applied to the visual controlling filter disposed in front of the screen of the CRT by means of the filter controlling means when the vehicle runs so that the light from the display device in the direction toward the driver's seat is interrupted. Although, at this time, the display device screen can be viewed through the visual controlling filter from the passenger's seats except the driver's seat, the transmission characteristic of the visual controlling filter becomes different according to the wavelength of the light when the visual controlling filter is operated (the voltage is applied to the visual controlling filter). Therefore, when the operation of the visual controlling filter is detected, the color hue controlling circuit is operated to control the color hue of the displaying apparatus. Thus, even if the visual controlling filter is operated or not operated, the images transmitted and viewed through the visual controlling filter are not changed and can be viewed as the same color images.

Consequently, all viewers in any direction can observe the images on the CRT screen with no unpleasant feeling.

It will fully be appreciated by those skilled in the art that the foregoing description has been made in terms of the preferred embodiments and various changes and modifications may be made without departing from the scope of the present invention which is to be defined by the appended claims.