Abstract:
A high intensity lamp system for a motorcycle incorporating a plurality of commercially available integral reflector halogen lamps within a crossmember element of a motorcycle triple tree assembly. A control system continually adjusts the power delivered to the lamps to maintain safe operating temperature to maximize bulb life at light intensity levels consistent with vehicular applications for headlighting applications. This is achieved using lamps not intended for sealed operation and the high shock and vibration environment of a vehicular or motorcycle application. A microprocessor-based digital control system of the preferred embodiment permits additional control and continual adjustment of lamp power to eliminate visible dimming of the lamps dependant on engine speed and state of the vehicle charging system, which dimming is evident in prior art use of high intensity lamps operating at light output levels reduced from maximum ratings for bulb life considerations.

Description:
RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS  
       [0001]     This Application draws priority from a pending U.S. Provisional Application Ser. No. 60/540,928, filed Jan. 30, 2004. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to motorcycles; more particularly, to headlight means for a motorcycle; and most particularly, to method and apparatus for mounting and operating commercially available high-intensity lamps within a motorcycle triple tree crossmember to provide headlight operation within safe operating limits and acceptable lamp life.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known in the art of motorcycle headlight design to provide for a variety of streamline shapes for a motorcycle headlight housing and faring in conjunction with the so-called “triple tree” arrangement wherein a steering fork is pivotably mounted to a motorcycle frame, defining a steering head. See, for example, U.S. Pat. Nos. D374,730; D423,126; and D495,815S. Further, in some applications it is desired for style and/or speed purposes that the relatively large headlight and associated housing of a conventional prior art motorcycle headlight assembly be completely eliminated, as by embedding of a headlight function within a vehicle&#39;s structural members which provides the look and line as if there were no headlight at all, yet the headlight function is retained in a position and location ideal for headlight performance.  
         [0004]     Commercially available high intensity lamps, such as integral reflector halogen lamps, can provide high levels of light output consistent with requirements for vehicular headlights in a relatively small volume and form factor. Such lamps, having integral polished reflectors, can provide shaped beams in 10 to 20 degree angle spotlight configurations that are well-suited to vehicular headlight applications.  
         [0005]     High intensity halogen lamps in a motorcycle application are subject to high power density and thermal dissipation limitations and to a shock/vibration environment for which commercially available, integral reflector halogen lamps are not intended nor inherently well-suited. Such lamps are designed and intended for use in residential/commercial interior lighting applications with constant available power, adequate ventilation for cooling, and low-shock environment. Experience has shown that operation of such halogen lamps at their fully specified light output levels and power input ratings in a sealed, vehicular environment results in an unacceptably shortened bulb life and consequent failure.  
         [0006]     What is needed in the art of motorcycle headlights is an arrangement wherein a conventional large and obvious headlight housing is obviated.  
         [0007]     What is further needed in the art of motorcycle headlights is a halogen lamp system having high reliability, long lifetime, and constant light output under all operating conditions.  
         [0008]     It is a primary object of the invention to eliminate a conventional large and obvious headlight housing from a motorcycle assembly.  
         [0009]     It is a further object of the invention to provide a compact motorcycle headlight system having high reliability, long lifetime, and constant light output under all operating conditions.  
       SUMMARY OF THE INVENTION  
       [0010]     Briefly described, a motorcycle headlight system in accordance with the invention comprises a plurality of reflector-type halogen lamps disposed in a housing formed as a triple tree crossmember of a motorcycle (also referred to herein simply as a “triple tree” as is well known in the motorcycle arts).  
         [0011]     High beam and low beam headlight operation are on/off controlled by conventional handlebar mounted switches.  
         [0012]     Control circuitry extends lamp lifetime by operating the lamps at less than full power ratings. A desired light output level for a vehicular headlight is obtained by using a plurality of lamps, all being operated at derated power levels. An automatic control circuit for safe operation of multiple lamps in derated mode over wide ambient temperature ranges and input supply voltages is provided to achieve long bulb life and light output performance expected of typical vehicular headlights. By applying a pulse width modulated (PWM) control signal, the average current and thus average power can be controlled to maintain acceptable headlight intensity and color temperature. PWM switching is performed at a rate far faster than the response time of the bulb filaments such that no perceptible flicker occurs from the pulsed control waveform.  
         [0013]     The control PWM generator accepts a temperature sensing element input from a thermistor or similar resistance varying element over ambient temperature. The temperature sensing element is mounted in proximity to the lamp heat source and circuitry most susceptible to damage due to excess temperatures. The sensor generates an error voltage and the PWM generator proportionally reduces the duty cycle of the control signal to maintain the assembly at or below the safe operating temperature. In the event the internal temperature falls, due, for example, to better heat dissipation resulting from increased windspeed around the housing or night operation in the absence of solar thermal loading, the PWM generator proportionally increases the duty cycle to achieve maximum permissible power and headlight output.  
         [0014]     The halogen control assembly has an under/over supply voltage sensor detecting the difference from the nominal 12 vdc supply and applies this error to the PWM generator. By applying a reduced duty cycle waveform to the control switches proportional to the overvoltage error, the halogen lamps can be operated safely in the expected, naturally occurring overvoltage conditions of high engine speed and a fully charged battery. Conversely, an undervoltage error signal results in a higher duty cycle from the PWM generator to prevent annoying headlight yellowing at low engine speed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0016]      FIG. 1  is an isometric view of a prior art motorcycle headlamp housing for attachment to a triple tree crossmember;  
         [0017]      FIG. 2  is an isometric view from below of a motorcycle steering head showing a triple tree crossmember containing headlamps in accordance with the invention;  
         [0018]      FIG. 3  is an isometric view from above of the steering head shown in  FIG. 2 ;  
         [0019]      FIG. 4  is an isometric view from the left side of the steering head shown in  FIGS. 2 and 3 ;  
         [0020]      FIG. 5  is a plan view from above of a triple tree crossmember in accordance with the invention;  
         [0021]      FIG. 6  is a plan view from below of the triple tree crossmember shown in  FIG. 5 ;  
         [0022]      FIG. 7  is a front elevational view of the triple tree crossmember shown in  FIGS. 5 and 6 ;  
         [0023]      FIG. 8  is an cross-sectional view taken along line  8 - 8  in  FIG. 7 ;  
         [0024]      FIG. 8   a  is an exploded isometric view of a triple tree crossmember assembly in accordance with the invention;  
         [0025]      FIG. 9  is a block diagram of a function for controlling a headlight system in accordance with the invention; and  
         [0026]      FIG. 10  is a schematic electrical diagram of the headlight system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring to  FIG. 1 , a prior art headlight housing  10  for mounting adjacent to a prior art motorcycle triple tree  12  is shown, substantially as disclosed in U.S. Pat. No. Des. 374,730, issued Oct. 15, 1996 to Hauser. Housing  10  clearly demonstrates the benefit of a headlight mounting that is positioned by a triple tree crossmember, but housing  10  still presents a bulky and protrusive form for carrying a headlight well ahead of and sdeparate from the triple tree. Further, this design patent is silent as to the type and number of lamps for which the housing is suitable. Housing  10  does not suggest the benefit of forming the triple tree crossmember itself as a housing for one or more miniature high-intensity lamps and control circuitry, as is novelly described and claimed herein.  
         [0028]     Referring to  FIGS. 2 through 4 , a steering head  14 , in accordance with the invention, for a motorcycle (not shown) defines a pivot post  16  fixedly disposed on the motorcycle, right and left steering fork tubes  18   a , 18   b , and one or more triple trees, preferably two spaced apart vertically as triple trees  20   a , 20   b , pivotably connecting the steering fork tubes to the pivot post via openings  21 . Preferably, both triple trees are provided with bearings  24  ( FIGS. 6,8 ) in known fashion in openings  22   a ,  22   b  for smooth, durable steering rotation of the triple trees on the pivot post.  
         [0029]     Referring to  FIGS. 5 through 8   a , lower triple tree  20   b  in accordance with the invention is formed of a strong, lightweight material such as aluminum, titanium, or other metal or metal alloy, or an organic polymer. Triple tree  20   b  is so formed as to function structurally as a conventional triple tree crossmember and also as a housing for one or more headlamps  28 . Lateral portions of triple tree  20   b  comprise left and right mounting clamps  30   a ,  30   b  having openings  32   a ,  32   b  for receiving fork tubes  18   a ,  18   b . Each clamp includes a compression allowance slot  34   a ,  34   b  and compression screws  36   a ,  36   b  threaded into bores to permit secure tightening of triple tree  20   b  onto the fork tubes at any desired location along the tubes, consistent with the length of pivot post  16 .  
         [0030]     A housing  26  is formed centrally of triple tree  20   b  comprising a top wall  38 , rear wall  40 , side walls  42   a ,  42   b , and a front wall  44 , and enclosing a chamber  46 . Chamber  46  is open  48  on an underside  50  of triple tree  20   b . In use, opening  48  is hermetically sealed via a cover plate  63  ( FIG. 8   a ) secured by bolts (not shown) in bores  52 .  
         [0031]     In the currently-preferred embodiment  20   b  shown in  FIGS. 2 through 8   a , within chamber  46  are a microprocessor  120  and associated control cuircuitry  200  for controlling operation of one or more lamps  28 . Lamp  28  comprises first and second low-beam lamps  114  disposed on either side of a central high-beam lamp  112 , the lamps being positioned within chamber  46  adjacent to ports  56  in front wall  44 . Housing  26  is formed such that front wall  44  forms an angle  58  ( FIG. 4 ) with the walls of openings  32   a ,  32   b  such that wall  44  is substantially vertical when the triple tree is installed for use on the forks and pivot post of a motorcycle. Preferably, each port  56  is closed by a shatter-proof lens element  60  to protect lamps  112 ,  114 . Preferably, high beam lamp  112  is mounted in housing  26  such that the axis of the beam extending through lens  60  is substantially parallel in use to a road surface; low-beam lamps  114  preferably are depressed by about 2 degrees with respect to the high beam lamp. As described above, each lamp  28  is preferably a commercially available integral reflector halogen lamp although other types of lamps are fully comprehended by the invention.  
         [0032]     Each lamp  112 ,  114  is supported by a light can  54  and extends through an opening in a shim plate  55  to which it is locked by a lock plate  57 . Shim plate  55   a  for high-beam lamp  112  contains 0o wedge, while shim plates  55   b  contain a 2o vertical wedge. A mounting plate  59  secures the internal lamp assembly to housing  26 , and an insulator plate  61  shields microprocessor  120  and circuitry  200  from the heat of the lamps. Cover plate  63  closes chamber  46  as described above.  
         [0033]     Referring to  FIG. 9 , a control function for a motorcycle headlight system in accordance with the invention is shown in block diagram  100 . This control function, although shown here exemplarily for a motorcycle headlight system, is suitable for use with any halogen-type lamp system wherein a constant color temperature and lamp intensity are desired over a range of electrical and thermal conditions.  
         [0034]     A conventional motorcycle 12-volt charging system  102  and a 12-volt battery  104  provide nominal 12-volt current  106  to high-beam switch  108  and low-beam switch  110 , which may be separate switches or a toggle switch. The switches control one or more high-beam lamps  112  and one or more low-beam lamps  114 , respectively. The lamps are preferably high-intensity halogen lamps as described above. Preferably, all lamps are identical, and high-beam and low-beam refer only to the angle the lamp forms with the roadway surface, as just described.  
         [0035]     Lamps  112 ,  114  are grounded through first and second FET electronic switches  116 ,  118 , respectively. Switches  116 ,  118  are controlled by a microprocessor  120  and associated circuitry as described below ( FIG. 10 ), including a pulse width modulated (PWM) control generator which generates an output signal  119  to open and close on a specified duty cycle  121 , variable by microprocessor  120  between 5% 123 and 95%  125 , whereby any lamps whose switches  116 ,  118  are closed are pulsed at a high frequency, as described below. Because the lamps generate heat that can be detrimental to lamp life, a temperature sensing element  122  is disposed in proximity to the lamps and sends a signal  124  to microprocessor  120  which adjusts the PWM duty cycle as needed to avoid damage to the lamps. Further, an undervoltage sensor  126  detects low voltage in the electric generating system and sends a signal  128  to the microprocessor  120  to adjust the PWM duty cycle to maintain a desired color temperature of lamp output.  
         [0036]     Referring to  FIG. 10 , a preferred embodiment  200  of an overall control function for a motorcycle headlight system uses an all digital, low-parts-count, microprocessor control based circuit. A microprocessor controller  120  is an ideal logic level, variable width pulse generator with an internal time base. It provides straightforward interface to logic level Field Effect Transistor (FET) switches  116 ,  118  to control the halogen lamps and offers design flexibility to accommodate optional additional functions, for example, flash control for optional integral turn signal lamps which may be embedded in the headlight assembly.  
         [0037]     A microprocessor controller in accordance with the invention preferably operates under a resident firmware program to execute the control function steps as internally clocked at the rate governed by the R 1 , C1 pair setting the internal master clock. The processor operation counts down the master clock to a program controlled number of clock cycles and then toggles the control lines to the Q1 and Q2 switches  116 ,  118  and continually repeats this process. In this way, a control waveform of on and off states is generated many hundreds of times per second to achieve flicker free, PWM control of lamp brightness and thermal power to be dissipated.  
         [0038]     The ratio of on time to off time, or duty cycle of the control waveform, is continually updated under program control by simply adjusting the number of clock cycles to be counted down. At the start of each repetitive count down cycle, U1 microprocessor  120  executes a read of the digital number available at the U2 and U5 analog to digital (A/D) converters. These devices generate a digital word proportional to the voltage present at their input pins and serially send this word to U1 microprocessor  120  over the Data Out (DO) line when commanded by the states of the Chip Select(CS) and Clock(CLK) lines. U1 microprocessor  120  uses these digital words under program control to either add to or subtract from the on time count and proceeds with the PWIM control waveform generation. Timing associated with the read of the U2 and US A/D&#39;s is kept very short compared to the PWM waveform generation cycle such that the processor is spending the vast majority of the time simply counting down clock cycles to toggle the Q1 and Q2 control lines from on to off.  
         [0039]     Temperature control of the headlight assembly is achieved by creating a temperature dependant voltage at the input of the U2 A/D converter. The VR1 thermistor  122  changes resistance across its sensed temperature range. By creating a voltage divider circuit between VR1 and the bias resistor R 2 , a temperature dependant voltage can be applied to the U2 input proportional to the resistance of the VR1 thermistor. The temperature set point can be adjusted by changing the value of the Radj resistor R 3 . In this way, the U2 will send a digital word proportional to the temperature-dependant sensed input analog voltage when commanded by U1 microprocessor  120 . When the sensed temperature is below the set point, U1 microprocessor  120  adds to the on time count, resulting in more power being applied to the lamps and more thermal power to be dissipated, resulting in a slow temperature rise internal to the assembly. When the temperature rises above the set point, U1 microprocessor  120  conversely subtracts from the on time count, resulting in less power to be dissipated and a cooling of the assembly. With the relatively long thermal time constant to heat and cool the assembly, a smooth and virtually imperceptible change in the light output level is effected to maintain the assembly at the set point temperature.  
         [0040]     Under- and over-voltage conditions resulting from the battery state and charging system conditions can adversely impact lamp life or result in a perceptible lamp output yellowing. These conditions are controlled by the U5 A/D converter circuit. The supply voltage to the halogen lamp assembly is monitored by sensor  126  for variation above or below the nominal +12 vdc. Again, a digital word is sent by the U5 A/D converter to U1 microprocessor  120  proportional to the sensed difference above or below the nominal 12 dc supply voltage.  
         [0041]     Sensing of the supply voltage is made by the U4 operational amplifier circuit. The U4 reference input pin (−) is held at a constant +5 vdc using the Zener diode Z 1  biased with R 7 . The R 4  and R 5  pair forms a 2 to 1 divider such that the 10 to 15 vdc supply voltage will be halved to 5 to 7.5 vdc at their connection point. This 5 to 7.5 vdc level is applied to the input of U4 operational amplifier through R 6 . The feedback resistor R 8  is selected such that the U4 will provide a DC gain of 2 to the difference in voltages between the +input and the −reference input held at the constant 5 v level. This results in a 0 to +5 vdc output level corresponding to the instantaneous level that the supply voltage is above the nominal low of 10 volts. The 0 to 5 volt sensed level is applied to the U5 A/D converter where a digital word is generated proportional to the level across the 0 to 5 volt input range. When polled by U1 microprocessor  120 , this digital word is serially sent and used to adjust the on time of the PWM control signal. For supply voltages in excess of the nominal +12 vdc, the digital word is subtracted from U1 microprocessor&#39;s on time count, resulting in lower average current through the lamps and providing protection from stressing the lamps in this over voltage case.  
         [0042]     When the battery supply voltage falls below the nominal +12 vdc, the on time of the PWM control signal is proportionally increased to provide higher average current and a brighter lamp to hold the light output at the equivalent of the nominal +12 V supply input. Timing of this sensing and correction action is fast enough to not result in perceptible change in light output. In this way the halogen lamps are protected from potential over-voltage stress, and the annoying yellowing of the headlight color temperature is eliminated under under-voltage conditions.  
         [0043]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.