Abstract:
The high-intensity discharge lamps lighting apparatus includes an adjusting means that adjusts a pulse width of a rectangular-wave AC voltage. By controlling the pulse width of the rectangular-wave AC voltage using the adjusting means, the pulse width of the rectangular-wave AC voltage applied to the high-intensity discharge lamp is changed, thereby an emission color of the high-intensity discharge lamp can be adjusted.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a high-intensity discharge lamp lighting apparatus for turning on a light source of lighting equipment for a vehicle lamp such as a headlamp of a four-wheeled automotive vehicle or a two-wheeled automotive vehicle. This invention also relates to a lighting driving method therefor.  
         [0003]     2. Description of the Related Art  
         [0004]     A discharge tube called “high-intensity discharge lamp (hereinafter “HID lamp”)” is used as a light source for vehicles. The lighting equipment including this HID lamp will be referred to as an “HID lamp lighting apparatus” hereinafter.  
         [0005]      FIG. 4  is a block diagram of a conventional HID alternating-current (AC) lighting apparatus. Conventional techniques related to the present invention will be described with reference to  FIG. 4 .  
         [0006]     Normally, an HID lamp  4  includes two electrodes, and a voltage at a rated voltage of several, tens of volts to several hundreds of volts is applied to between the electrodes of the HID lamp  4  through a signal path  70  so as to maintain stable electric discharge. In addition, it is necessary to cause a dielectric breakdown by applying a high voltage of about 20 kilovolts between the electrodes of the HID lamp  4  for a short time so as to start the electric discharge. To this end, an igniter  7  is provided as a trigger circuit.  
         [0007]     A battery  1  shown in  FIG. 4  is a power supply of an automotive vehicle. An output voltage is normally a DC voltage of 12 volts for an ordinary-size vehicle, and a DC voltage of 24 volts for a large-sized vehicle. To obtain a voltage at a rated voltage of several tens to several hundreds of volts, a DC-DC converter  2  that raises the DC voltage of 12 volts to several hundreds of volts is provided.  
         [0008]     In case of the AC lighting system, an AC voltage at the frequency of about 250 Hz is applied to the HID lamp  4  in an ordinary lighting operation. This AC voltage is obtained by converting a DC voltage into the AC voltage using a DC-to-rectangular-wave AC conversion circuit  3 . As a result, the HID lamp  4  emits a light with a color tone characteristic of the HID lamp  4 . It should be noted that the above-mentioned frequency of the AC voltage is only one example.  
         [0009]     A light emission principle of the HID lamp is as follows.  
         [0010]     A high-voltage pulse is applied between electrodes provided in a light emitting tube, and discharged in a filler gas, thereby a mercury-metal compound provided in the light emitting tube is evaporated, and a light is stably emitted.  
         [0011]     The color tone of the HID lamp depends on the type of filler gas, electrode material, electrode structure, catalyst, therefore, emission spectrum depends on a characteristic of the HID lamp itself.  
         [0012]     An HID lighting apparatus in which two HID lamps are simultaneously turned on has a disadvantage in that it is difficult to make irregularities in color tones of the two lamps uniform. To make the irregularities in color tones of the two lamps uniform, a replacement operation for replacing the HID lamps by trial and error is required.  
         [0013]     An index that physically and objectively represents a color tone is a color temperature in kelvins (K). If a color temperature is low, a color tone is reddy. If the color temperature is high, the color tone is bluey. It is said that a human visibility is high for a reddy emission color, particularly high for irregularities on a road surface.  
         [0014]     As a lighting apparatus for changing over a plurality of lamp colors using one lamp, “a lamp color changeover apparatus” disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 7-134902 is known. This apparatus disadvantageously has a complicated mechanical configuration, so that the apparatus cannot be attached without changing an attachment structure.  
         [0015]     As the HID lamp lighting apparatus, the HID lamp lighting apparatus disclosed in Tsutomu Shiomi, Takashi Kambara, et al., “Ballasts for HID Headlamp Systems for Automobiles”, Matsushita Electric Works, Ltd. Technical Report, May 2001, pages 13 to 19 is known.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention has been achieved in the light of the conventional disadvantages. It is an object of the present invention to provide a novel high-intensity discharge lamp lighting apparatus capable of easily making irregularities in color tones of two lamps uniform, and independently adjusting the color tones irrespectively of the number of high-intensity discharge lamps to be attached, without changing an attachment structure of the high-intensity discharge lamps, or particularly a novel high-intensity discharge lamp capable of changing a color tone of an emission color of each HID by a user&#39;s operation, and a lighting driving method therefor.  
         [0017]     The present invention achieves the above-noted objects by adopting the following technical constitutions.  
         [0018]     The first aspect of the present invention is a high-intensity discharge lamp lighting apparatus comprising: a high-intensity discharge lamp to which a low-frequency rectangular-wave AC driving signal is applied; and adjusting means for adjusting a pulse width of the low-frequency rectangular-wave AC driving signal; wherein a color tone of a light emitted from the high-intensity discharge lamp being controlled by changing the pulse width of the rectangular-wave AC driving signal by the adjusting means.  
         [0019]     The second aspect of the present invention is a method for driving a high-intensity discharge lamp to which a low-frequency rectangular-wave AC driving signal is applied, an emitted light of the high-intensity discharge lamp having a first spectrum included in a light output in a first period starting from a signal polarity commutation point of the low-frequency rectangular-wave AC driving signal and a second spectrum included in a light output in a second period subsequent to the first period; the method comprising the steps of: controlling the pulse width of the rectangular-wave AC driving signal; and changing a mixture ratio of the first spectrum to the second spectrum; thereby a color tone of said light emitted from the high-intensity discharge lamp being controlled.  
         [0020]     The third aspect of the present invention is a high-intensity discharge lamp lighting apparatus comprising: a high-intensity discharge lamp to which a low-frequency rectangular-wave AC driving signal is applied, an emitted light of the high-intensity discharge lamp having a first spectrum included in a light output in a first period starting from a signal polarity commutation point of the low-frequency rectangular-wave AC driving signal and a second spectrum included in a light output in a second period subsequent to the first period; signal generating means for generating the low-frequency rectangular-wave AC driving signal, a period of which is a sum of the first period and the second period; and ratio changing means for changing a ratio of the first period to the second period; thereby a color tone of a light emitted from the high-intensity discharge lamp being controlled by changing the ratio of the first period to the second period.  
         [0021]     The fourth aspect of the present invention is a method for driving a high-intensity discharge lamp to which a low-frequency rectangular-wave AC driving signal is applied, wherein an emitted light of the high-intensity discharge lamp having a first spectrum included in a light output in a first period starting from a signal polarity commutation point of the low-frequency rectangular-wave AC driving signal and a second spectrum included in a light output in the second period subsequent to the first period; the method comprising the steps of: generating the low-frequency rectangular-wave AC driving signal, a period of which is a sum of the first period and the second period; and adjusting a mixture ratio of the first spectrum generated in the first period to the second spectrum generated in the second period; thereby a color tone of a light emitted from the high-intensity discharge lamp being controlled.  
         [0022]     The fifth aspect of the present invention is a method in which the first period is a period in that a waveshape of the driving signal varies with a convexed configuration or with a concaved configuration, while the second period is a period in that a waveshape of the driving signal shows a relatively stable configuration.  
         [0023]     According to the present invention, even after the HID lamp lighting apparatus is attached to a vehicle, the color tone of the light emitted from the HID lamp can be arbitrarily changed by a user&#39;s operation. Therefore, a novel function that enables to set an appropriate brightness and an appropriate color tone in accordance with a surrounding environment of the vehicle can be realized.  
         [0024]     The property in which an object appears different according to a light source is called “color rendering”. The present invention enables this color rendering to be arbitrarily changed by one HID lamp lighting apparatus without replacing one lamp with another lamp. For example, the lamp according to the present invention can be normally employed by increasing a color temperature, i.e., at a high Kelvin temperature, and employed in a foggy atmosphere by reducing the color temperature, thereby a visibility can be enhanced. Driver&#39;s safety is improved, accordingly.  
         [0025]     Further, the present invention exhibits the following excellent advantages. Since the color tone can be adjusted, colors emitted from left and right front lights can be easily made uniform, and an HID lamp replacement operation can be simplified. The replacement operation for replacing the HID lamps by trial and error so as to make the irregularities in color tones of the two lamps uniform is particularly eliminated.  
         [0026]     An attachment time can be reduced, accordingly.  
         [0027]     Moreover, a structure of the lamp according to the present invention is not a special structure and a conventionally standard structure can be used. The HID lamp lighting apparatus according to the present invention is advantageously low in cost and easy to carry out.  
         [0028]     Additionally, the HID lamp lighting apparatus according to the present invention can be used for illumination of a product showroom, a show window, or the like, and can emit a light equal in spectrum to a natural light such as “daytime light in a fine weather”, “light in a cloudy weather”, or “solar light at noon” so that an attractive appearance of a product sensitive to a light can be produced. The present invention can be, therefore, applied to various fields. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a block diagram that depicts a configuration of an HID lamp lighting apparatus according to one embodiment of the present invention;  
         [0030]      FIG. 2  is a waveform view that depicts a waveform of a driving signal applied to an HID lamp of the HID lamp lighting apparatus according to the embodiment of the present invention;  
         [0031]      FIGS. 3A  to  3 C are driving signal waveform views for illustrating a control method for changing a color tone;  
         [0032]      FIG. 4  shows a measurement example of a spectral distribution characteristic of the HID lamp lighting apparatus according to the present invention;  
         [0033]      FIG. 5  shows a measurement example of the spectral distribution characteristic of the HID lamp lighting apparatus according to the present invention; and  
         [0034]      FIG. 6  is a block diagram of a conventional HID AC lamp lighting apparatus. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]     An embodiment of the present invention will be described hereinafter with reference to the drawings.  
         [0036]     An operation principle of the present invention will be first described with reference to  FIGS. 2 and 3 .  
         [0037]      FIG. 2  is a waveform view that depicts a waveform of a driving signal applied to an HID lamp of the HID lamp lighting apparatus according to the present invention.  
         [0038]     Referring to  FIG. 2 , a driving signal for an HID lamp of the HID lamp lighting apparatus according to the present invention is a rectangular-wave AC signal. This rectangular-wave AC signal is a signal which has a repetition period Tb, and a polarity of which is changed from a positive polarity to a negative polarity or vice versa in a half period Ta.  
         [0039]     It is assumed herein that a period in which a waveform is transiently changed to a crest (or a trough) from a signal polarity commutation point (a pulse rising or falling point)  90  is T 1 , and that a subsequent stationary period is T 2 . In the period T 1 , a transient phenomenon depending on the HID lamp occurs right after the signal polarity commutation point. The period T 1  in which this phenomenon occurs is characteristic of each HID lamp and is a substantially constant value (period).  
         [0040]     An optical spectrum of the HID lamp generated in the period T 1  exhibits a characteristic that a reddish light at a low color temperature is emitted. An optical spectrum thereof generated in the period T 2  has a characteristic that a light at a higher color temperature is emitted. Due to this, a human vision recognizes an optical spectrum that is a mixture of the two optical spectrums in the periods T 1  and T 2 . A change in color tone resulting from this mixture can be controlled by changing a ratio of the period T 1 , which is a transient response period, to the period T 2 , which is a stationary period. Namely, by changing the period T 2 , the optical spectrum that is a mixture of the two optical spectrums can be changed. In this case, the repetition cycle may be constituted so that the periods T 2  are continuously changed or discretely changed.  
         [0041]     A specific example will be described. When the HID lamp is driven in the cycle, with the period T 1  of 150 μS and the period T 2  of 2 milliseconds, the color temperature of the HID lamp is 4000 K. If the period T 2  is gradually lengthened from 2 milliseconds, the color temperature is raised from 4000 K toward 5000 K. If the period T 2  is gradually shortened from 2 milliseconds, the color temperature is lowered from 4000 K toward  3000 K.  
         [0042]     According to the preset invention, attention is paid to the fact that each HID lamp has a characteristic optical spectrum in the period T 1 . Therefore, the present invention provides a novel HID lamp lighting apparatus that includes an adjustment means for changing the period T 2 . By allowing the adjustment means to change an emission spectrum component of an HID lamp  4  according to a change in the period T 2 , an emission color of the HID lamp  4  can be adjusted.  
         [0043]      FIGS. 3A  to  3 C are driving signal waveform views for illustrating an HID lamp driving method for changing the color tone of the HID lamp  4 .  
         [0044]     If the transient response period T 1  and the stationary period T 2  are applied to waveforms shown in  FIGS. 3A, 3B , and  3 C, a color tone in  FIGS. 3A, 3B , and  3 C depends on a ratio of T 1  to T 2 , a ratio of T 1  to T 2 ′, a ratio of T 1  to T 2 ″, respectively. Since the periods T 2 , T 2 ′, and T 2 ″ satisfy a relationship of T 2 &lt;T 2 ′&lt;T 2 ″, the emission color is closer to a bluish color, that is, the color temperature of the emission color is higher in this order.  
         [0045]     A relationship among the periods T 1  and T 2 , the half period Ta, and the period Tb of the driving signal is represented by the following Equations (Eq. 1) to (Eq. 4). 
 
 Ta=T   1 + T   2   (Eq. 1) 
 
 Tb=Ta× 2=( T   1 + T   2 )×2  (Eq. 2) 
 
         [0046]     If the Equations (Eq. 1) and (Eq. 2) are divided by T 2 , respectively, the following Equations (Eq. 3) and (Eq. 4) can be given. 
 
 Ta/T   2 = T   1 / T   2 +1  (Eq. 3) 
 
 Tb/T   2 =( T   1 / T   2 +1)×2  (Eq. 4) 
 
         [0047]     In the Equations, T 2 &gt;&gt;T 1  and T 1  is a fixed value. If T 2  is changed to T 2 ′, T 2 ″, . . . , the ratio of T 1  to T 2 , i.e., T 1 /T 2  is changed according to the Equations (Eq. 1) to (Eq. 4).  
         [0048]     The instance in which a length of period is elongated from T 2  to T 2 ″ has been described above. Conversely, if the period T 2  is shortened as T 2 ″ to T 2  in this order, the emission color is closer to a reddish color, that is, the color temperature is lower in this order.  
         [0049]     As stated above, the control over the ratio of the transient response period T 1  to the stationary period T 2 , as the principle of the present invention, can be easily and arbitrarily exercised.  
         [0050]      FIGS. 4 and 5  show measurement examples of a spectral distribution characteristic (optical spectrum charts) of the apparatus according to the present invention. The spectral distribution characteristic represents an optical energy according to each wavelength. In  FIGS. 4 and 5 , a horizontal axis indicates an optical wavelength (in nanometers (nm)) and a vertical axis indicates optical energy. The spectral distribution characteristics shown in  FIGS. 4 and 5  are obtained by driving the same HID lamp using the same circuit, and equal in all conditions except for a driving period. The spectral distribution characteristics shown in  FIGS. 4 and 5  differ in energy distribution according to the optical wavelengths. This comparison, therefore, shows that the present invention is effective.  
         [0051]     An instance of a rectangular wave duty ratio of 50% has been described. Alternatively, the duty ratio may be other than 50%.  
         [0052]     A constitution of the present invention to realize the above-stated operation will be described.  
         [0053]      FIG. 1  is a block diagram that depicts a configuration of the HID lamp lighting apparatus according to one embodiment of the present invention. Since the apparatus shown in  FIG. 1  is almost equal in configuration to the conventional apparatus shown in  FIG. 6 , the same constituent elements as those shown in  FIG. 6  are denoted by the same reference symbols.  
         [0054]     Referring to  FIG. 1 , the HID lamp lighting apparatus differs from the conventional apparatus shown in  FIG. 6  in part of a DC-to-rectangular-wave AC conversion circuit  3  and a switching signal generation circuit  8  that drives switching elements.  
         [0055]     A battery  1  supplies a DC voltage of 12 volts to a DC-DC converter  2  via signal paths  11  and  12 . The DC-DC converter  2  converts the DC voltage of 12 volts into a DC voltage of several tens to several hundreds of volts, and outputs the resultant DC voltage to signal paths  21  and  22 .  
         [0056]     The DC-rectangular-wave AC conversion circuit  3  converts the DC voltage of several tens to several hundreds of volts between the signal paths  21  and  22  into a rectangular-wave AC signals at 250 to 500 hertz, and outputs resultant AC signals to signal paths  61  and  62 , respectively. The signals between the signal paths  61  and  62  have the signal waveform shown in  FIGS. 2 and 3 A to  3 C. The switching signal generation circuit  8  is a generation circuit that generates a signal at 250 to 500 hertz. This switching signal generation circuit  8  is composed by a rectangular-wave generation circuit  82  and a driving circuit  81 . The repetition period, i.e., the repetition frequency of the rectangular-wave output from the rectangular-wave generation circuit  82  can be arbitrarily set by an operation panel  9 . The rectangular-wave signal output from the rectangular wave generation circuit  82  is supplied to switching elements  31 ,  32 ,  33 , and  34  in the DC-rectangular-wave AC conversion circuit  3  through the driving circuit  81 , so as to control switching of the switching elements  31  to  3 . 4 . The DC-rectangular-wave AC conversion circuit  3  outputs a rectangular-wave signals, as shown in  FIGS. 2 and 3 A to  3 C, to the signal paths  61  and  62 . An igniter  7  supplies a high-voltage pulse to the HID lamp  4  only when starting to turn on the HID lamp  4 .  
         [0057]     With the above-stated configuration and operation, the signal shown in  FIGS. 2 and 3 A to  3 C is supplied to the HID lamp  4  through signal paths  71  and  72 , thereby the emission color of the HID lamp  4  can be changed.  
         [0058]     The operation panel  9  in this embodiment may be an ON/OFF switchover device using a button, a continuously variable switchover device such as a slide resistor, a multipoint switchover device of selecting several types, or the like. A setting of the switchover may be a semi-fixed setting using a tool such as a driver. This switchover may be either continuously variable switchover or discrete switchover.  
         [0059]     Further, an HID lamp color temperature detecting means may be provided in place of the operation panel  9  so as to control the color temperature of the emission light to be equal to a preset color temperature.