Abstract:
A vehicle having an internal combustion engine that drives a generator and a cranking motor that cranks the engine is provided with a standard electrical system as well as a supplemental electrical system. This supplemental electrical system includes a capacitor that is charged by the primary electrical system of the vehicle and is protected against excessive discharge. When it is desired to start the engine, the capacitor is connected to the cranking motor to supply adequate cranking power to the cranking motor, regardless of the state of charge of the batteries.

Description:
BACKGROUND 
     The present invention relates to vehicles of the type that include an internal combustion engine, a cranking motor, and a battery normally used to power the cranking motor. In particular, this invention relates to improvements to such systems that increase of the reliability of engine starting. 
     A problem presently exists with vehicles such as heavy-duty trucks. Drivers may on occasion run auxiliary loads excessively when the truck engine is not running. It is not unusual for heavy-duty trucks to include televisions and other appliances, and these appliances are often used when the truck is parked with the engine off. Excessive use of such appliances can drain the vehicle batteries to the extent that it is no longer possible to start the truck engine. 
     The present invention solves this prior or problem in a cost-effective manner. 
     SUMMARY 
     The preferred embodiment described below supplements a conventional vehicle electrical system with a capacitor. This capacitor is protected from discharging excessively when auxiliary loads are powered, and it is used to supply a cranking current in parallel with the cranking current supplied by the vehicle battery to ensure reliable engine starting. A battery optimizer automatically increases the voltage to which the capacitor is charged as the capacitor temperature falls, thereby increasing the power available for engine cranking during low temperature conditions. 
     This section has been provided by way of general introduction, and it is not intended to limit the scope of the following claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an electrical system for a vehicle that incorporates a preferred embodiment of this invention. 
     FIG. 2 is a graph illustrating operation of the circuit  42  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning down to the drawings, FIG. 1 shows an electrical system of a vehicle  10  that includes an internal combustion engine  12 . The engine  12  can take any suitable form, and may for example be a conventional diesel or gasoline engine. The engine  12  drives a generator  14  that generates a DC voltage. As used herein, the term “generator” is intended broadly to encompass the widest variety of devices for converting rotary motion into electrical power, including conventional alternators, generators, and the like. The engine  12  is also mechanically coupled to a cranking motor  16 . The cranking motor  16  can take any suitable form, and it is conventionally an electrical motor that is powered during cranking conditions by current from a storage battery  18  such as a conventional lead acid battery. Current from the battery  18  is switched to the cranking motor  16  via a switch such as a conventional solenoid switch  20 . The solenoid switch  20  is controlled by a conventional starter switch  22 . 
     All of the elements  10  through  22  described above may be entirely conventional, and are well-known to those skilled in the art. The present invention is well adapted for use with the widest variety of alternative embodiments of these elements. 
     In addition to the conventional electrical system described above, the vehicle  10  also includes a supplemental electrical system including a capacitor  30 . The capacitor  30  is preferably a double layer capacitor of the type known in the art has an electrochemical capacitor. Suitable capacitors may be obtained from KBI, Lake in the Hills, IL under the trade name KAPower. For example, in one alternative the capacitor  30  has a capacitance of 1000 farads, a stored energy capacity of 60 kilojoules, an internal resistance at −30 degrees Celsius of 0.004 ohms, and a maximum storage capacity of 17 kilowatts. In general, the capacitor should have a capacitance greater than 320 farads, and an internal resistance at 20° C. that is preferably less than 0.008 ohms, more preferably less than 0.006 ohms, and most preferably less than 0.003 ohms. The energy storage capacity is preferably greater than 15 kJ. Such capacitors provide the advantage that they deliver high currents at low temperatures and relatively low voltages because of their unusually low internal resistance. Further information about suitable capacitors for use in the system of FIG. 1 can be found in publications of ESMA, Troitsk, Moscow region, Russia and on the Internet at www.esma-cap.com. 
     The capacitor  30  includes a negative terminal that is connected to system ground, and a positive terminal that is connected to the electrical system of the vehicle via a first signal path  32  and a second signal path  36 . The first signal path  32  is used for charging the capacitor  30 , and it includes two circuits  34 ,  42 . The first circuit  34  operates to prevent excessive discharging of the capacitor  30 . The circuit  34  can take many forms. In one example, the circuit  34  includes a low voltage disconnect circuit that disconnects the capacitor  30  from the electrical system of the vehicle when the voltage on the first path  32  falls below a preselected level. For example, the circuit  34  may open the first path  32  when the voltage on the first path  32  falls below 11.8 volts. Higher or lower voltages may be used. In this example, the capacitor  30  receives charging currents from the generator  14  via the first path  32 , and the capacitor  30  supplies current to various loads in the electrical system of the vehicle until the voltage in the first path  32  falls below the selected level. A suitable device for performing this function can be obtained from Sure Power Industries, Inc., Tualatin, Oreg. as model number 13600. 
     In another example, the circuit  34  may simply include a suitably sized diode oriented to pass charging currents from the generator  14  to the capacitor  30  while blocking discharging currents from the capacitor  30  via the first path  32 . Many other alternatives are possible, as long as the first circuit  34  achieves the desired function of protecting the capacitor  30  against excessive discharge, thereby ensuring that the capacitor  30  maintains an adequate charge to start the engine  12 . 
     The circuit  42  is included in the first path  32  to optimize the charging voltage applied to the capacitor  30  for the presently prevailing temperature. The circuit  42  increases the charging voltage applied to the capacitor  30  at low temperatures, when engine starting requirements are increased and conventional battery performance is decreased. FIG. 2 shows one example of a suitable voltage profile as a function of temperature. Note that the temperature is preferably the temperature of the capacitor  30 , and the charging voltage applied to the capacitor  30  is greater below a selected temperature (such as zero degrees Celsius) than it is at a higher temperature (such as +30 degrees Celsius). The profile of FIG. 2 is intended by way of example and many other profiles can be used, including profiles that are continuous in slope as well as stepwise profiles. 
     The circuit  42  can take many forms. For example, a conventional battery optimizer can be used, such as that supplied by Purkey&#39;s Fleet Electric, Inc., Rogers, Ariz. Such battery optimizers control the voltage applied to the voltage sense input of the generator  14 , thereby altering the regulated voltage generated by the generator  14 . Alternately, the circuit  42  can include a DC to DC converter that converts a voltage generated by the generator  14  to the desired charging voltage, which can vary as a function of temperature in accordance with the profiles discussed above. 
     The second path  36  connects the capacitor  30  to the cranking motor  16  via a high amperage switch  38 . The switch  38  may for example be a MOSFET switch such as that sold by IntraUSA under the trade name Intra switch. 
     The switch  38  is controlled by a switch controller  40  that is in turn coupled with the starter switch  22  of the vehicle  10 . The controller  40  holds the switch  38  in an open circuit condition except when the starter switch  22  commands engine cranking, at which time the switch  38  is closed. Thus, the controller  40  causes the switch  38  to be closed during cranking conditions and opened during non-cranking conditions. The controller  40  can take many forms, including conventional analog and digital circuits. Microprocessors can also readily be adapted to perform the functions of the controller  40 . It is not essential in all cases that the switch  38  be in an open circuit condition at all times other than when the engine  12  is being cranked. For example, the controller  40  may allow the switch  38  to remain in the closed circuit condition after engine cranking has terminated, as long as the voltage supplied by the capacitor  30  does not fall below a desired level, one that which the capacitor  30  stores sufficient power to start the engine  12  reliably. In this case, the first path  32  and the circuit  34  may be eliminated, and the circuit  42  may be placed in the second path  36 . 
     The system of FIG. 1 provides a number of important advantages. 
     First, the supplemental electrical system including the capacitor  30  provides adequate current for reliable engine starting, even if the battery  18  is substantially discharged by auxiliary loads when the engine  12  is not running. If desired, the supplemental electrical system including the capacitor  30  may be made invisible to the user of the vehicle. That is, the vehicle operates in the normal way, but the starting advantages provided by the capacitor  30  are obtained without any intervention on the part of the user. 
     Additionally, the capacitor  30  provides the advantage that it can be implemented with an extremely long life device that can be charged and discharged many times without reducing its efficiency in supplying adequate cranking current. 
     As used herein, the term “coupled with” is intended broadly to encompass direct and indirect coupling. Thus, first and second elements are said to be coupled with one another whether or not a third, unnamed, element is interposed therebetween. For example, two elements may be coupled with one another by means of a switch. 
     The term “battery” is intended broadly to encompass a set of batteries including one or more batteries. 
     The term “set” means one or more. 
     The term “path” is intended broadly to include one or more elements that cooperate to provide electrical interconnection, at least at some times. Thus, a path may include one or more switches or other circuit elements in series with one or more conductors. 
     Of course, many alternatives are possible. The functions of the elements of  34 ,  38 ,  40 ,  42  may if desired all be integrated into a single device. Is anticipated that such integration may simplify packaging requirements and reduce manufacturing costs. Any appropriate technology can be used implement the functions described above. 
     The foregoing description has discussed only a few of the many forms that this invention can take. For this reason, this detailed description is intended by way of illustration, not limitation. It is only the claims, including all equivalents, that are intended to define the scope of this invention.