Abstract:
A two-wheeled electric scooter principally powered by batteries which together provide more than 100 volts. The scooter carries an onboard recharging system to replenish the battery supply. Accordingly, the onboard recharging system is not called upon to provide the main power source for acceleration and other operating conditions. A recharging system is implemented either as a fuel cell which trickle charges the battery, or an internal combustion engine which recharges the battery through a mechanical charging unit such as an alternator or generator. Regenerative braking is provided so as to further conserve energy by back driving the motor to recharge the battery pack during braking. Connections are provided for an external power source such as an AC outlet to be plugged into the scooter so as to provide an alternate mechanism to recharge the batteries.

Description:
RELATED APPLICATIONS 
     NONE 
     TECHNICAL FIELD 
     The present invention relates to electric scooters in which an on-board charging system is provided to recharge the batteries. 
     BACKGROUND OF THE INVENTION 
     Electric scooters are well known in the prior art. Typically electric scooters have a bank of batteries which provide power to drive the motor. These batteries must be recharged from time to time. This is typically done by plugging the batteries into an AC power outlet for some period of time to restore the depleted energy. Recharging circuits for electrical scooters, such as that disclosed in U.S. Pat. No. 5,965,996, have been developed for the purpose of uniformly charging batteries. In the aforementioned &#39;996 patent a total of ten 12 volt batteries are provided on the scooter. Due to the weight and volume of so many batteries, scooters may need to develop special frames or the like to support this added weight and volume. U.S. Pat. No. 6,047,768 is directed to a scooter frame which can accommodate ten such 12-volt batteries. 
     In recent years, there has been considerable interest in placing battery recharging units and battery energy conserving units permanently onboard electric vehicles. U.S. Pat. No. 5,631,532 entitled “Fuel cell/battery hybrid power system for vehicle” exemplifies the use of a fuel cell to recharge a battery in an electric vehicle. U.S. Pat. No. 5,713,426 discloses the use of regenerative braking to returning energy by back-driving the motor mechanism. However, neither of these references disclose such device in conjunction with an electric scooter. 
     What is desirable is an electric scooter which has an onboard charging system that recharges batteries, the batteries being used as the principal power source to propel the scooter. 
     SUMMARY OF THE INVENTION 
     The present invention is realized by a two-wheeled electric scooter having a frame sufficient to accommodate batteries which collectively provide the capacity to propel the scooter at accelerations and velocities comparable to that of general traffic flow. In addition to a frame and batteries, the electric scooter of the present invention includes an electric motor, an onboard recharging source for recharging the batteries, an interface to an external power source for rapid recharging of the batteries and control and monitoring mechanisms to help regulate battery consumption and restoration. 
     In one aspect of the invention, the recharging source is a fuel cell which provides a trickle charge to the batteries through a DC-DC converter. Either methanol or hydrogen may be used as the fuel to drive the fuel cell as appropriate. 
     In another aspect of the invention, the charging source is an internal combustion engine using either gasoline, diesel or other fuel, which charges the batteries via a mechanical charging unit such as an alternator or generator. 
     In yet another aspect of the present invention, regenerative braking circuit is supplied which charges the batteries with energy harnessed during deceleration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can better be understood through the attached figures in which: 
     FIG. 1 shows a functional block diagram of the components used to support the present invention; 
     FIGS. 2 a  and  2   b  show a side and a plan view, respectively, indicating the arrangements of the various components of FIG. 1 in an electric scooter; 
     FIG. 3 shows a DC-DC converter in accordance with one embodiment of the present invention; 
     FIG. 4 shows a step-up converter of the sort used in the DC—DC converter of FIG. 3; 
     FIG. 5 diagrams a motor controller of the sort used in the present invention; 
     FIGS. 6 a  &amp;  6   b  show velocity profiles as a function of time, for both extra urban and urban scooter travel, respectively; 
     FIGS. 7 a - 7   c  show the arrangement of different types of batteries in a scooter; and 
     FIGS. 8 a  &amp;  8   b  show rider and corresponding battery state of charge (SOC) as profiles for scooter use. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The aforementioned U.S. Pat. Nos. 5,965,996, 6,047,768, 5,631,532 and 5,713,426 are incorporated by reference to the extent necessary to understand the present invention. 
     FIG. 1 presents a block diagram showing the functional components associated with the present invention. An electric scooter motor  100  provides the driving power to drive the scooter. Preferably scooter motor  100  is a three-phase slotted brushless permanent magnet motor, specially made by Kollmorgen Corporation (www.kollmorgen.com) for the present purposes. While Table 1 below lists the specifications of the motor used in a preferred embodiment of the present invention, it should be kept in mind that countless other specifications may also suffice. 
     Scooter motor  100  receives a three-phase voltage from scooter motor controller  102 . Preferably scooter motor controller  102  outputs a variable waveform, such as pulse width modulation, to drive the scooter motor  100 . The scooter motor controller  102  includes high power semiconductor switches which are gated (controlled) to selectively produce the waveform necessary to connect the battery pack  104  to the scooter motor. 
     Battery pack  104  preferably includes sufficient batteries connected in series to output at least 100 VDC as discussed further below. The battery pack  104  preferably comprises either lead-acid batteries or Ni—Zn batteries. Regardless of which types of batteries are used, it is crucial for the purposes of the present invention that the batteries be rechargeable. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Motor Parameters @ 25° C. &amp; 120 VDC 
               
             
          
           
               
                 Characteristic 
                 Feature 
               
               
                   
               
               
                 Type 
                 Permanent magnet 
               
               
                 Peak Power 
                 20 kW 
               
               
                 Peak Torque 
                 65.6 N-m 
               
               
                 Current @ Peak Torque 
                 325 Amps 
               
               
                 Maximum Speed 
                 5500 RPM 
               
               
                 Maximum Winding Temperature 
                 155° C. 
               
               
                 Temperature rise per Watt 
                 0.5° C./watt without forced air 
               
               
                 Continuous Torque 
                 22.8 N-m 
               
               
                 Airgap 
                 0.082 inches 
               
               
                 Winding DC Resistance 
                 63 mΩ ± 10% 
               
               
                 Winding Inductance 
                 80 mH ± 30% 
               
               
                 Number of Poles 
                 8 
               
               
                 Rotor Inertia 
                 0.0093 kg-m 2   
               
               
                 Motor Weight 
                 7.7 kg maximum 
               
               
                 Number of Phases 
                 3 
               
               
                 Winding Configuration 
                 Wye 
               
               
                 Lamination Material 
                 Low Loss Iron 
               
               
                 Slot configuration 
                 Straight 
               
               
                 Stator Inside Dimension 
                 5.8 inches (147 mm) 
               
               
                 Stator Outside Dimension 
                 7.3 inches (185 mm) 
               
               
                 Stator Stack Length 
                 1.95 inches (50 mm) 
               
               
                 Static Friction 
                 0.8 N-m 
               
               
                 Torque Sensitivity 
                 0.118 N-m per Ampere Peak 
               
               
                 Back EMF Constant 
                 0.118 Volts per Radian per Second 
               
               
                 Magnet Material 
                 Neodymium Iron Boron 
               
               
                 Cooling 
                 Passive via Motor Side Swingarm 
               
               
                 Winding Insulation 
                 Nema Class H, min withstand 600 V 
               
               
                   
                 RMS 
               
               
                   
               
             
          
         
       
     
     A conventional battery charger  106 , is one way in which the battery pack  104  is recharged. Battery charger  106  may reside onboard the scooter and is connectable to an AC outlet via a plug  108  or the like. Alternatively, the battery charger  106  may remain off of the vehicle and be connected to the scooter only during high current charging sessions. 
     In addition to the battery charger  106 , which connects to an AC outlet to recharge the battery pack, an onboard charging system  110  is also provided on the scooter. The onboard charging system comprises an onboard power generating source  112 , a fuel supply  114  which feeds the onboard power generating source  112 , and a converter/charge controller  116  which transforms the output of the onboard power generating source  112  into a form suitable for charging the battery pack  104 . 
     A scooter controller  118  sends signals to the motor controller  102 , the battery charger  106  (when provided onboard the scooter), the onboard power generating source  112 , and the converter/charge controller  116 . The charge of the battery pack is monitored via a battery monitor  120  which, in turn, is connected to the scooter controller  118  to provide information which may affect the operation of the scooter controller. The energy state of the battery pack is displayed on a battery gauge  122  so that the user can monitor the condition of the battery pack, much like a fuel gauge is used a gasoline powered scooter. The status of the fuel supply  114  is similarly displayed on a fuel gauge  124  for the user&#39;s convenience. 
     FIGS. 2 a  and  2   b  show many of the block diagram components of FIG. 1 as arranged on a motor scooter  130 . Scooter  130  has a scooter frame  132  not unlike that shown in U.S. Pat. No. 6,047,786. The battery pack  104  is arranged so that the scooter has a relatively low center of gravity. While FIGS. 2 a  and  2   b  show the battery pack to be a linear arrangement of batteries having substantially similar vertical positions, it should be kept in mind that the batteries may be arranged in different configurations so as to optimize space in the scooter frame. The onboard power generation source  112  is seen in FIG. 2 a  to be positioned just above the battery pack with the fuel supply  114  positioned thereabove. Preferably, the fuel supply  114  is easily accessible from outside the scooter so as to facilitate both refueling and replacement. The fuel supply  114  may be integrally formed with the onboard power generation source  112 . The scooter motor  100 , along with its associated gear box, drives the rear wheel  134  of the scooter and is positioned in the vicinity of the frame  132  and the rear wheel  134 . The scooter motor controller  102  is positioned near the interior portion of the frame so as to minimize the distance between it and the motor  100 . The battery charger  106  is preferably positioned and close to the battery pack and therefore at a relatively low position so as to facilitate connection to an external power supply. Lastly, the battery gauge  122  and the fuel supply gauge  124  are positioned near the front of the scooter so as to facilitate viewing by a user. 
     In a first preferred embodiment, the onboard power generating source  112  is a fuel cell and the fuel supply  114  is either hydrogen or methanol depending on the nature of the fuel  112 . In a preferred embodiment, a Power PEM-PS® family fuel cell available from H-power (www.hpower.com) is used. This family of DC power sources based on a fuel cell provides approximately 250-500 watts continuously. Such a system operates on ambient air and clean pressurized hydrogen fuel from the fuel tank  114 . This type of fuel cell comprises a cell stack of a proton exchange membrane type (PEM), mechanical auxiliaries and an electronic control module. A fuel cell such as this provides a relatively low power onboard power source which operates at a continuous, steady state output. This provides a constant trickle charge to the battery pack  104  via the DC—DC converter/charge controller. As stated above, the fuel cell  112  normally works on a continuous basis. However, it may selectively be turned on or off via the scooter controller  118 . 
     FIG. 3 shows a DC—DC converter/charge controller  116  which can be used to convert the output of the fuel cell  112  into a voltage suitable for charging the battery pack  104 . The converter/charge controller comprises a pair of step-up converters  116   a,    116   b  arranged in parallel. Though only two converters are shown here, it should be kept in mind that any number of converters may connected in parallel to deliver the current required by the battery to sustain effective charging. The step-up converters  116   a,    116   b  preferably have an input voltage range on the order of 28-40 VDC and output approximately 140 VDC at 0.5 amps. Positive output terminals of the step-up converters  116   a,    116   b  are passed through respective diodes  140   a,    140   b,  which preferably both are of the 1N4004 type. This is done to ensure that the battery bus voltage does not leak current back through the step-up converter in the event that the fuel cell is switched off. The output from the step-converters is combined at a positive node  142   a  and negative node  142   b.  Node  142   a  is connected to a 20 ohm, 25 watt current limiting resistor  144 . In this manner, the DC—DC converter/charge controller provides an output of approximately 138 volts at a maximum draw of 2 amps at output port  146 . 
     FIG. 4 depicts an exemplary step-up (boost) converter  116   a,    116   b.  A step-up (boost) converter is used to produce higher voltage at the load than at the supply voltage. When power switch Q 2  is on, the inductor L is connected to the DC source at the input port  148  and the energy from the DC source is stored in the inductor L. When the power switch Q 2  is switched off, the energy stored in the collapsing field of inductor L causes the voltage on the anode of diode D 2  to rise sharply. Current flowing through diode D 2  raises the voltage on filter capacitor Co. In this manner, the output voltage at the output port  150  is higher than the voltage at the input port  148 . 
     As seen in FIG. 3, the output port  146  of the DC—DC converter  116  is applied to a charge controller  160 . Charge controller  160  is of the sort described in U.S. Pat. No. 5,965,996. Charge controller  160  is capable of controlling power to a nominal 120 volt DC battery pack  114 . The charge controller  160  charges a battery pack first using a constant current until the battery pack reaches 140 volts, then applies a constant voltage at 140 volts and then reapplies a constant current until the battery pack reaches 156 volts. Each of these voltage set points may be specified under the control of the scooter controller. In this respect, the scooter controller enables the DC—DC converter  116  to continue to charge the battery pack via the charge controller  160  until the battery becomes fully charged or the operator elects to shut down the system. In this manner, the charge controller provides over-current and over-voltage limit protection. Furthermore, the charge controller is configured to minimize ripple current applied to the battery pack and is also configured to provide temperature compensation consistent with the variability of gassing voltage requirements. 
     The battery gauge  120  preferably comprises a collection of LEDs and optimally also includes a traditional analog or digital gauge in addition to the LEDs to convey the state of battery charge. With regard to the LEDs associated with the battery gauge, a red LED, when lit, indicates that the fuel cell is active; a yellow LED, when active, indicates that the battery pack is charged to a predetermined percentage, e.g. 80%; and a green LED, when lit, indicates that the battery pack is fully charged. In this manner, the battery gauge informs a user of the status of the battery pack. 
     FIG. 5 illustrates the scooter motor controller  102  of the present invention in conjunction with the scooter motor  100  and the battery pack  104 . Motor controller  102  preferably comprises a controller device such as the Ti-TMS 320F240 DSP chip available from Texas instruments. The scooter motor controller  102  comprises three model no. CM400DU-12H IGBT&#39;s made by Powerex (www.pwrx.com) of Youngwood, Pa. These IGBT&#39;s have a peak rating of 400 amps and 600 volts and can sustain a maximum continuous current of 100 amps. The DSP chip preferably applies a switching frequency of 16 kHz using a six step sine wave switching mode via the IGBT&#39;s. The input voltage applied to the IGBT&#39;s is the 120 volt nominal battery bank  104  which may be implemented either as lead-acid batteries typically having an 80-130 volt operating range, or Ni—Zn batteries having a 90-140 volt operation range. 
     As a practical matter, individuals using a scooter for purely urban operation have different power and endurance requirements than individuals using a scooter in extra urban environments. This is because in urban environments, the distances traveled are short, there is frequent stopping and starting, and average speeds are low. This places one set of demands upon an electric scooter. In contrast, extra urban settings are characterized by infrequent stops and starts with sustained periods of high velocity travel. This places a different kind of demand upon an electric scooter. FIG. 6 a  shows time vs. speed profile  170  for a single trip. Each of curves  172 ,  174 ,  176  represents the time-speed profile for a single stop/start leg during the single trip. As seen in the profile  170  the maximum duration of any of the legs is somewhat less that 100 seconds and the maximum speed reached during any of these legs is on the order of 50 km/hr. Thus, an electric scooter configured to operate efficiently in urban setting, must be able to accelerate and decelerate quite often, but need not maintain a high rate of speed for sustained periods of time. 
     As seen in FIG. 6 b,  an extra urban setting may require a scooter to sustain a velocity of at least 50 km/h for several hundred seconds in a single leg. Thus, a scooter configured to operate in an extra urban setting need not accelerate or decelerate as often but would be required to sustain high levels of speed. 
     Thus, it may be expedient to design an electric scooter based on the expected type of setting (urban vs. extra urban) in which that scooter is expected to operate. Accordingly, one may select the number and type of batteries used in the battery pack  104 , based upon the expected environment in which the electric scooter is to operate. It should be evident to one skilled in the art, that reducing the number of batteries, or the rating of batteries, in the aggregate, reduces costs of an electric scooter. Accordingly, economic benefits may be realized if electric scooters were designed with the intended operating environment in mind. FIG. 7 a  shows a scooter frame  190  holding ten 12 volt sealed lead-acid (SLA) batteries  192 , each battery having a 16 amp-hour rating for a total of approximately 1.9 kilowatt hours at 120 volts. 
     FIG. 7 b  shows the same frame holding ten 12 volt SLA batteries  194 , each battery having a rating of 26 amp-hours for a total of 3.1 kilowatt hours at 120 volts. Because the 26 amp-hour batteries  194  are larger than the 16 amp hour batteries, the larger batteries occupy more space in the frame. FIG. 7 c  shows a multiplicity of 24 amp-hour Ni—Zn batteries which have less mass for the same energy capacity relative to SLA batteries, albeit at higher cost. 
     FIG. 8 a  shows a speed profile and the state of charge (SOC) as a function of time for an electric scooter configured for extra urban driving, the scooter being provided with a 3.1 kilowatt capacity Ni—Zn battery pack and using dual 80 watt fuel cells arranged in parallel. During the morning commute, the battery SOC drops from 100% to 60%. During the work day, with the scooter parked and the fuel cell operating, the battery pack recovers to 90% SOC. At the end of the evening commute, the battery SOC is reduced to 50%. At rest overnight, the fuel cell will return the battery SOC to 100% to start the cycle over again, thus making the vehicle fully sustainable and consequently a reliable means for commuting. 
     FIG. 8 b  shows the speed and state of charge as a function of time for an electric vehicle configured for urban driving having a 1.9 kilowatt hour capacity Ni—Zn battery pack and a single 100 watt fuel cell. As compared to the commuting pattern shown in FIG. 8 a,  FIG. 8 b  has one fewer extra urban cycles in each of the morning and evening commute legs. The reduced battery capacity, however, is sufficient to sustain the vehicle as a viable means for the commuting pattern shown. 
     As seen in FIGS. 8 a  and  8   b,  the morning commute reduces the state of charge of a fully charged battery pack to a certain level and the state of charge recovers during the course of the day between the morning commute and the evening commute due to recharging caused by the fuel cell(s). However, the battery pack is not recharged in either FIG. 8 a  or  8   b  to 100 percent of its capacity. In both FIGS. 8 a  and  8   b,  during the evening commute, the state of charge is reduced gradually during the stop and go phase (presumably close to one&#39;s office) and is reduced considerably during the latter phase (presumably closer to one&#39;s home and away from the office area). Nevertheless, regardless of its initial capacity, the fuel cell is preferably able to fully charge the battery pack after day normal user. And on those days during which the vehicle is used more than normal, additional charging from an external power source may be used overnight to prepare the electric scooter for the following morning. 
     While both FIGS. 8 a  and  8   b  show that the state of charge is reduced somewhat steeply at the high speeds, it is noted that the state of charge in the electric scooter of FIG. 8 b  is decreased to a lesser extent than the electric scooter of FIG. 8 a  which is provided with a battery pack having a capacity of 3.1 kilowatt hours. 
     In a first preferred embodiment, the battery supply  104  comprises lead acid batteries available from the Hawker Energy Group at (www.hepi.com) of Missouri. Preferably, the lead acid batteries are either the Genesis model no. G16EP (16 Amp-hour) or model no. G26EP (26 Amp-hour). The lower amp-hour rating batteries are used when the scooter is designed to commute only a small distance within an urban area whereas the 26 amp-hour batteries are used when the scooter is designed to travel in suburban as well as urban areas with a longer commuting distance. 
     In a second preferred embodiment, nickel zinc (Ni—Zn) batteries may be used instead of the lead-acid type. Preferably sealed Ni—Zn batteries from Evercel Corporation (www.evercel.com) of Danbury, Conn., are used. Evercel&#39;s model nos. 25-12 and 40-12 batteries having a nominal voltage of 12 volts and a capacity of 22 and 30 Amp-hours, respectively, are suited for use in the present invention. 
     To charge the batteries from an external power source, a battery charger is required. For lead acid batteries, preferably, a model no. K2 battery charger available from Zivan of Poviglio, Italy is used. If, on the other hand, Ni—Zn batteries are used, a Zivan model no. NG3 battery charger is preferably used. Both battery chargers can be plugged into a 120 volt, 60 Hz AC power supply. For European and other uses, chargers capable of operating from a 220 volt, 50 Hz AC power supply are also available. 
     In the above embodiment, we have assumed that a fuel cell is used as the onboard recharging source  112 . In a second embodiment, the onboard recharging source is an internal combustion engine. In such case, preferably a Honda model no. EU100I engine is used. This engine has an integrated fuel tank and is manually started. The single phase engine drives a mechanical charging unit, such as an alternator or generator. The engine has a rated output of 900VA with a maximum output of 1000VA and cooperates with the mechanical charging unit to put out a 120 volt, 60 Hz signal for charging the batteries. This output is conditioned to provide appropriate charging of the battery pack. Furthermore, because the internal combustion engine is air-breathing, air inlet and exhaust hardware must be provided in this embodiment. In addition, a standard gasoline-type fuel gauge would be provided to inform the operator of the fuel level, as would a keyed switch to start and stop the engine. 
     Finally, while the above invention has been described with reference to certain preferred embodiments, it should be kept in mind that the scope of the present invention is not limited to these. One skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the claims set forth below.