Abstract:
The present invention relates to a liquid crystal display for a vehicle and, particularly, to a liquid crystal display which adjusts liquid crystal drive voltage based on the temperature of a liquid crystal display panel so that the contrast of the liquid crystal display panel is optimum. The display includes a liquid crystal display panel, a circuit board for mounting circuit elements including a liquid crystal driver, a temperature sensor mounted on the circuit board, and a control circuit for controlling liquid crystal drive voltage based on temperature detected by the temperature sensor. The liquid crystal display panel and the circuit board are arranged parallel to each other in a meter housing with a predetermined space therebetween. The display also includes an exposed heat collection panel arranged to surround the screen of the liquid crystal display panel. This configuration provide a liquid crystal display for a vehicle capable of controlling liquid crystal drive voltage accurately without mounting a temperature sensor on the liquid crystal display panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2001-063430, filed on Mar. 7, 2001, the entire contents thereof are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a liquid crystal display for a vehicle and, particularly, to a liquid crystal display which adjusts liquid crystal drive voltage based on the temperature of a liquid crystal display panel so that the contrast of the liquid crystal display panel becomes optimum.  
           [0004]    2. Description of Background Art  
           [0005]    In a liquid crystal display, the contrast of a liquid crystal display panel changes according to an ambient temperature environment even if liquid crystal drive voltage remains the same. Then, Japanese Laid-Open Patent Application No. 10-31204 proposes a liquid crystal display which automatically adjusts liquid crystal drive voltage based on the temperature of the liquid crystal panel detected by a temperature sensor such as a thermistor.  
           [0006]    In other words, the contrast of the liquid crystal display is correlated with its temperature. In order for the liquid crystals keep a high contrast between the time when liquid crystals are on in a transparent state, and the time when the liquid crystals are off in a non-transparent state, the drive voltage must be reduced as the temperature of the liquid crystals becomes higher. Therefore, in the above prior art, the ambient temperature of the liquid crystals is detected by a temperature sensor, and a temperature compensation circuit is provided to increase drive voltage when the ambient temperature drops. Likewise, this temperature compensation circuit reduces drive voltage when the ambient temperature rises.  
           [0007]    In the above prior art, the temperature of a liquid crystal display panel is represented by the detection temperature of a temperature sensor for detecting the inside temperature of a housing. However, in a liquid crystal display which is often exposed to direct rays of the sun as when it is employed as the meter panel of a motorcycle, a temperature difference occurs between the ambient temperature of the inside of the housing and the actual temperature of the liquid crystal display panel. This makes it difficult to apply the optimum liquid crystal drive voltage. To solve this technical problem, a technology for mounting a temperature sensor to a liquid crystal display panel is also proposed.  
           [0008]    However, when the temperature sensor is mounted to the liquid crystal display panel, an electrode for connecting this temperature sensor to a circuit board are newly required, thereby causing technical problems such as an increase in the number of parts or a complicated production process.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a liquid crystal display for vehicle panel which can control liquid crystal drive voltage accurately without mounting a temperature sensor to a liquid crystal display panel.  
           [0010]    To attain the above object, according to the present invention, a liquid crystal display for vehicle is provided with a liquid crystal display panel, a circuit board for mounting circuit elements including a liquid crystal driver, a temperature sensor mounted on the circuit board, and a control circuit, mounted on the circuit board, for controlling liquid crystal drive voltage based on the detection temperature of the temperature sensor. The liquid crystal display panel and the circuit board are arranged parallel to each other with a predetermined space therebetween in a meter housing. The display further comprises an exposed heat collecting panel arranged to surround the screen of the liquid crystal display panel.  
           [0011]    According to the above feature, when the temperature of the liquid crystal display panel is increased by exposure to sunlight, the inside of the apparatus is heated by the heat collection panel to keep the difference between the ambient temperature in the housing detected by the temperature sensor and the actual temperature of the liquid crystal display panel substantially constant. Therefore, since the temperature of the liquid crystal display panel can be judged accurately based on the detection temperature of the temperature sensor in a high temperature environment in which the appropriate range of liquid crystal drive voltage is narrow, drive voltage can be controlled to the optimum value based on the detection temperature of the temperature sensor.  
           [0012]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0014]    [0014]FIG. 1 is a front view of a liquid crystal display for vehicle according to the present invention;  
         [0015]    [0015]FIG. 2 is a sectional view cut on line II-II of FIG. 1;  
         [0016]    [0016]FIG. 3 is a diagram showing the relationship between the temperature Tq of a liquid crystal display panel and temperature T detected by a temperature sensor when a heat collection panel is not provided;  
         [0017]    [0017]FIG. 4 is a diagram showing the relationship between the temperature Tq of the liquid crystal display panel and temperature T detected by the temperature sensor when the heat collection panel is provided;  
         [0018]    [0018]FIG. 5 is a block diagram of the control circuit of the liquid crystal display for vehicle;  
         [0019]    [0019]FIG. 6 is a block diagram showing the constitution of the essential section of FIG. 5 functionally;  
         [0020]    [0020]FIG. 7 is a diagram showing the relationship between the temperature of the liquid crystal display panel and liquid crystal drive voltage; and  
         [0021]    [0021]FIG. 8 is a front view of the key section of a motorcycle provided with the liquid crystal display for vehicle of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Preferred embodiments of the liquid crystal display for vehicle according to the present invention will be described in detail with reference to the accompanying drawings.  
         [0023]    [0023]FIG. 8 is a front view of the essential section of a motorcycle provided with the liquid crystal display  1  for vehicle of the present invention. The liquid crystal display  1  for vehicle is mounted to a center portion of a handlebar  61  and winkers  37 L and  37 R are arranged on right and left sides of the handlebar  61  such that they project from the handlebar  61 . On the right side of the vehicle body of a leg shield  62  is arranged a power switch  38  which can be operated by a power key.  
         [0024]    A brake lever  39  for front wheels is provided on the right grip  61 R of the handlebar  61  and a brake lever  36  for rear wheels is provided on the left grip  61 L. Mirrors  46 L and  46 R are provided on left and right sides of the handlebar  61 .  
         [0025]    [0025]FIG. 1 is a front view of the liquid crystal display  1  for vehicle and FIG. 2 is a sectional view cut on line II-II of FIG. 1. Since the liquid crystal display  1  for vehicle of this embodiment is mounted to a vehicle in such a manner that it is inclined at an angle θ in a longitudinal direction, the sectional view of FIG. 2 is inclined at the angle θ.  
         [0026]    In this embodiment, an opaque support case  20  and a transparent case cover  21  constitute a housing and both are fixed to each other at three locations by screws  31 ,  32  and  33 . In the housing, a liquid crystal display panel  10  containing liquid crystals sealed up between two glass sheets  10   a  and  10   b  is held by a liquid crystal holder  16 . Process data such as vehicle speed, engine speed, water temperature and the amount of the residual fuel are displayed on this liquid crystal display panel  10 . A heat collection panel  11  having an opening  12  for exposing the screen  10 ′ of the liquid crystal display panel  10  is placed on the exposed side of the liquid crystal display panel  10  to surround the screen  10 ′ of the liquid crystal display panel  10 .  
         [0027]    The above heat collection panel  11  comprises an opaque resin panel  11   a  and an adiabatic cushion material  11   b  mounted on the rear side of the panel  11   a  to surround the above opening  12 . Therefore, the opaque resin panel  11   a  which is directly exposed to rays of the sun passing through the case cover  21  and the liquid crystal display panel  10  are in contact with each other through the above adiabatic cushion material  11   b . Since the above heat collection panel  11  is arranged such that it divides the inside space (see  22 ,  23  in FIG. 2) of the meter housing, the temperature change rates of the both spaces  22 ,  23  become equal to each other.  
         [0028]    The above liquid crystal holder  16  is placed upright on the circuit board  17  by its leg portions  14  and  18 . An illumination LED  15  is placed upright on the circuit board  17  and the end of the light emitting portion of the LED  15  is exposed outward from the opening formed in the heat collection panel  11 . Circuit elements such as an LCD driver for driving the liquid crystal display panel  10 , LED driver (not shown) for driving the illumination LED  15 , temperature sensor  51  for detecting the ambient temperature of the circuit board  17  and temperature detection circuit (not shown) for controlling the above LCD driver based on temperature information detected by the above temperature sensor  51  are mounted on the above circuit board  17 . The above liquid crystal display panel  10  and the circuit board  17  are electrically connected by an electrode  52 .  
         [0029]    [0029]FIGS. 3 and 4 show the actual temperature (Tq) of the above liquid crystal display panel  10  and the internal ambient temperature (T) detected by the above temperature sensor  51  when the above heat collection panel II is not provided (FIG. 3) and when the panel  11  is provided (FIG. 4).  
         [0030]    At night before a time t 0  or in the shade, the temperature Tq of the liquid crystal display panel and the detection temperature T are almost equal to each other. In contrast to this, when pseudo sunlight begins to be irradiated at a time t 0 , the difference between the temperature Tq of the liquid crystal display panel and the detection temperature T becomes larger along the passage of time as shown in FIG. 3 without the heat collection panel  11 . Therefore, there is a big difference between the temperature difference ΔT 1  at a time t 1  and the temperature difference AT 2  at a time t 2 .  
         [0031]    In contrast to this, since the detection temperature T of the temperature sensor  51  rises in the same manner as the temperature Tq of the liquid crystal display panel as shown in FIG. 4 when the heat collection panel  11  is provided, the difference between the both temperatures remains almost the same regardless of the passage of time. That is, the temperature difference ΔT 1  at a time t 1  and the temperature difference ΔT 2  at a time t 2  are almost equal to each other.  
         [0032]    Consequently, when the heat collection panel  11  is provided to surround the liquid crystal display panel  10 , the actual temperature Tq of the liquid crystal display panel  10  can be judged accurately simply by adding a compensation temperature ΔTadd equivalent to the above temperature difference ΔT 1  (=temperature difference ΔT 2 ) to the detection temperature T of the temperature sensor  51 .  
         [0033]    Further, as air warmed by heat generated by the heat collection panel and circuit elements is convected upward in the housing, the ambient temperature of an upper portion (space  22 ) has higher follow-up properties to the temperature rise of the liquid crystal display panel  10  than the ambient temperature of a lower portion (space  23 ). Since the temperature sensor is placed at a high position in space  23  while the liquid crystal display for vehicle is properly mounted on a vehicle in the above described embodiment, the follow-up properties of the detection temperature T to the temperature change of the liquid crystal display panel  10  are improved.  
         [0034]    [0034]FIG. 5 is a block diagram of the control circuit of the above liquid crystal display  1  for vehicle, wherein the same reference numerals as above denote the same or corresponding parts.  
         [0035]    An LCD driver  53  supplies a liquid crystal drive signal to the liquid crystal display panel (LCD)  10  in response to an instruction from a CPU  50 . The LED driver  54  supplies an LED drive current to an LED  15  in response to an instruction from the CPU  50 . A temperature detection circuit  56  converts the resistance value of the temperature sensor  51  (thermistor in this embodiment) into temperature information.  
         [0036]    The CPU  50  receives process data D such as vehicle speed and engine speed and outputs their segment data to the LCD driver  53 . Control programs and reference values are stored in a ROM  55 .  
         [0037]    [0037]FIG. 6 is a block diagram showing the constitution of the essential section of the above control circuit functionally, wherein the same reference numerals as above denote the same or corresponding parts.  
         [0038]    A function f(T) for controlling LCD drive voltage to an appropriate range based on the detection temperature T of the temperature sensor  51  is registered in the first storage portion  551  of the ROM  55 . A compensation temperature ΔTadd equivalent to the difference between the temperature Tq of the liquid crystal display panel and the detection temperature T is registered in the second storage portion  552 .  
         [0039]    The temperature compensation portion  502  of the CPU  50  outputs a switch signal Sch when the detection temperature T reaches a predetermined reference temperature Tref (45° C. in this embodiment). An adder  504  adds the detection temperature T of the temperature sensor  51  and the above compensation temperature ΔTadd. A switch portion  503  provides the detection temperature T to a drive voltage decision portion  501  when the switch signal Sch is not output from the above temperature compensation portion  502  and provides the total value ΔTadd+T) of the compensation temperature ΔTadd stored in the second storage portion  552  and the detection temperature T to the drive voltage decision portion  501  when the switch signal Sch is output.  
         [0040]    A decoder  505  converts the process data D into a segment signal to supply it to the LCD driver  53 . The drive voltage decision portion  501  determines LCD drive voltage based on the above function f(T) and temperature information provided from the above switch portion  503  to control the LCD driver  53 .  
         [0041]    In this constitution, when the detection temperature T of the temperature sensor  51  does not exceed the reference temperature Tref (45° C.), the detection temperature T is selected by the switch portion  503 . Therefore, the drive voltage decision portion  501  determines LCD drive voltage based on the function f(T) and the detection temperature T.  
         [0042]    In contrast to this, when the detection temperature T of the temperature sensor  51  exceeds the reference temperature Tref, the addition portion  504  is selected by the switch portion  503 . Therefore, the drive voltage decision portion  501  determines LCD drive voltage based on the function f(T) and the total temperature (ΔTadd+T).  
         [0043]    [0043]FIG. 7 is a diagram showing the relationship between the temperature Tq of the liquid crystal display panel and LCD drive voltage in this embodiment.  
         [0044]    The liquid crystal display panel  10  is blackened when its LCD drive voltage exceeds an appropriate range and whitened when the LCD drive voltage falls below the appropriate range. Although the upper limit voltage Vmax and the lower limit voltage Vmin of the appropriate range fall as the temperature rises, since the reduction rate of the upper limit voltage Vmax is larger than the reduction rate of the lower limit voltage Vmin, the appropriate range of the LCD drive voltage narrows as the temperature of liquid crystals increases.  
         [0045]    In contrast to this, as the detection temperature T can represent the temperature Tq of the liquid crystal display panel accurately until the detection temperature T of the temperature sensor  51  exceeds 45° C. in this embodiment as shown in FIG. 4, the LCD drive voltage can be set to an almost intermediate level of the appropriate range based on the above function f(T) and the detection temperature T.  
         [0046]    As the total value (T+ΔTadd) of the detection temperature T and the compensation temperature ΔTadd can represent the temperature Tq of the liquid crystal display panel accurately when the detection temperature exceeds 45° C., the LCD drive voltage can be set to an almost intermediate level of the appropriate range based on the above function f(T) and the total value (T+ΔTadd).  
         [0047]    The novel combination of elements of the present invention as described above, results in a liquid crystal display that is both accurate and easy to use.  
         [0048]    Specifically, a heat collection panel is provided to surround the liquid crystal display panel so that the detection temperature T of the temperature sensor rises, keeping a constant temperature difference from the temperature Tq of the liquid crystal display panel when the temperature Tq of the liquid crystal display panel is increased by exposure to direct rays of the sun. Thus, simply by adding the above temperature difference to the detection temperature T, the temperature Tq of the liquid crystal display panel can be judged accurately based on the detection temperature T of the temperature sensor.  
         [0049]    Also, since the temperature sensor is installed at a high position while the liquid crystal display for vehicle is properly mounted slant to a vehicle, the follow-up properties of the detection temperature T to a change in the temperature Tq of the liquid crystal display panel improve. Thus, the temperature Tq of the liquid crystal display panel can be judged more accurately based on the detection temperature T of the temperature sensor.  
         [0050]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.