Electric vehicle having a dual battery system

A computer controlled electric vehicle is disclosed that includes two high power batteries, a motor drive circuit, an electric motor that drives the vehicle drive train, a generator, an internal combustion engine, and battery charging circuitry. The batteries are connected to the motor drive circuit in a mutually exclusive fashion where only one battery is online or connected at any given time and the other battery is offline. The offline battery is recharged by battery charging circuitry that receives its power from a generator that is mechanically driven by an onboard hydrocarbon engine. When the online battery is depleted, the computer disconnects the online battery from the motor drive circuit and connects the offline battery to the motor drive circuit. The depleted battery is then charged in readiness for the next battery switch event. An external power plug enables recharging of the batteries when external power is available.

FIELD OF THE INVENTION

This invention relates to motorized vehicles and more particularly to electric vehicles and hybrid vehicles.

BACKGROUND OF THE INVENTION

Electric vehicles are well known in the prior art. Two common variations on such vehicles include purely electric vehicles having a rechargeable battery and an electric motor for driving the wheels, and hybrid vehicles including a combination of electric motor and internal combustion engine drive capability for delivering power to the wheels of the vehicle.

A distinct disadvantage associated with purely electric vehicles is the need to recharge the battery when the battery has been discharged as a result of vehicle use or due to an extended idle time span during which the vehicle battery was not charged. Battery technology has advanced in recent years with the advent of rapid charging battery chemistries, yet the time required for battery charging is still significant.

Further advances in battery technologies should result in smaller batteries with higher charge capacities directly affecting the physical space required for the battery compartment in an electric vehicle. Smaller battery space requirements and, more importantly, faster battery charging cycle times will ultimately benefit the electric vehicle industry yet further advances to take advantage of such battery improvements are needed, specifically an electric vehicle whose design fully contemplates these advances in technology.

SUMMARY OF THE INVENTION

An electric vehicle according to one aspect of the present invention comprises a passenger vehicle having four wheels, an electric motor having an output shaft mechanically coupled to and driving at least one of the four wheels, an accelerator transducer that produces a speed control signal in accordance with mechanical input from an operator of the vehicle, motor drive circuit means for producing a motor drive signal in accordance with the speed control signal, the motor drive circuit means including a motor power input for connection to a source of electrical power to produce the motor drive signal, and wherein the motor drive signal is supplied to the electric motor, a first battery, a second battery, an electric power generator having an input shaft, an internal combustion engine having an output shaft coupled to the input shaft of the electric power generator and wherein the internal combustion engine is optimized for efficiency to operate the electric power generator at a predetermined generator speed, charging circuit means for producing a charging signal, the charging circuit means receiving a power signal from the electric power generator; and, switch means for connecting the first battery and the second battery to the motor drive circuit means and the charging signal, the switch means operating in a first mode of operation to connect the first battery to the motor power input of the motor drive circuit means and connecting the second battery to the charging signal, the switch means operating in a second mode of operation to connect the second battery to the motor power input of the drive circuit means and connecting the first battery to the charging signal, and wherein the switch means operates in the first mode of operation while the charge state of the first battery is above a predetermined charge level and the switch means operates in the second mode of operation while the charge state of the second battery is above the predetermined charge level.

One object of the present invention is to provide an improved electric vehicle.

Another object of the present invention is to utilize two separate high output batteries to drive the electric motor of an electric vehicle.

Still another object of the present invention is to provide a charging mechanism for recharging a discharged battery while enabling continued operation of an electric vehicle.

These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 1, a diagrammatic illustration of an electric vehicle10according to the present invention is shown. Vehicle10includes vehicle computer12which manages a dual battery electric drive system and an on board battery charging and power generation system. Computer12monitors and controls the various system components shown to operate vehicle10in a power and fuel efficient fashion. Computer12includes a bi-directional data link14for receiving digital data from and issuing digital data commands to motor drive circuit16, electric drive motor18, battery charging circuitry20and internal combustion engine22. The output shaft of drive motor18is mechanically coupled to vehicle axle23so that tires25rotate in accordance with the rotation of the output shaft of motor18. Motor18is preferably a direct current motor.

Input devices connected to computer12include on/off switch24for enabling and disabling system operation and accelerator pedal26which produces a continuously variable analog signal corresponding to the position of the accelerator pedal, similar to throttle position sensors used with internal combustion engines of the prior art. Computer12directly controls the energized state of relays28and30and energizes, in a mutually exclusive manner, one of the relays28or30in accordance with algorithms discussed below to connect a high voltage signal from either battery32or battery34to motor drive circuit16. Accelerator pedal28supplies a speed signal to computer12and in accordance with the speed signal computer12controls motor drive circuit16to produce a power signal supplied to drive motor18. Alternatively, accelerator pedal28may be connected directly to motor drive circuit16and computer12would then receive pedal position data from motor drive circuit16and also enable and disable the output of drive circuit16for safety reasons.

System information is displayed by computer12via driver display and control interface36. Interface36also provides a multitude of vehicle system control inputs for the vehicle operator to enter commands for computer12to respond to, such as heating and air conditioning controls, vehicle lighting controls, wiper controls, radio and navigation electronics and other accessories typically found on motorized vehicles. System information displayed by computer12on display interface36includes, but is not limited to, current vehicle operation parameters such as vehicle speed, battery charge/health state for batteries32and34, battery currently connected to motor drive circuit16, estimated battery life based on current load factors, and estimated time to recharge off line battery.

Computer12provides closed loop control over the operating parameters of engine22to achieve superior efficiency of operation. Alternatively, engine22may include a separate computer based engine controller that communicates with computer12over data link14to receive operational commands and provide operational data to computer12. It is contemplated that all necessary electronic input sensors and output control devices well known in the internal combustion engine art are monitored or controlled by computer12via data link14. In addition, computer12controls the engaged or disengaged state of clutch38. Clutch38mechanically connects the output shaft of engine22to the input shaft of generator40when clutch38is engaged or actuated. Engine22includes an air conditioning compressor for passenger compartment cooling and a power steering pump to provide a power assist to vehicle steering gear. The air conditioning compressor and power steering pump are optional items as it is contemplated such accessory devices may be eliminated to improve overall system efficiency and vehicle mileage capability. Engine22also includes an alternator for producing a low voltage charging signal supplied to vehicle systems battery48on signal path47and for providing electrical power to sensors and electrical devices requisite for operation of an internal combustion engine.

Generator40produces a power output signal42that is supplied to battery charging circuit20. Battery charging circuit20produces independent and sophisticated battery charge signals on signal paths44and46in accordance with commands from computer12. High power rechargeable batteries, such as lithium-ion cells, require sophisticated charging signals with proper voltage and current levels applied to the battery during the charging cycle to achieve a fully charged battery in a minimum amount of time. Computer12monitors and controls charging circuit20to achieve the most efficient and expedient battery charging cycles in accordance with well known battery chemistry prior art.

External power plug50provides an external electrical connection to vehicle10so that electrical power from an electric power grid or source of electrical power may be supplied to charging circuit20, thereby enabling offline charging of batteries32and34when vehicle10is not mobile and placed in an “off” or “standby” state by the operator. When connected to external power, charging circuit20signals computer12to disable electric drive motor18thereby preventing movement and corresponding damage to vehicle10when a power cable is currently attached to power plug50. Alternatively, a simple limit switch mounted on power plug50and actuated when a power cable is connected to plug50could signal computer12to disable drive motor18and prevent vehicle movement.

Operationally speaking, drive motor18will operate from one of the two batteries32or34during normal operation, that is, either relay28or relay30is energized in a mutually exclusive manner by computer12to provide a power signal to motor drive circuit16and subsequently enable power to motor18in accordance with vehicular speed and acceleration desired by the user. User desired speed and acceleration are determined by computer12from the position of accelerator pedal26factoring in current vehicle speed and acceleration. Internal combustion engine22operates in one of two distinct modes of operation, a first low power or idle mode where clutch38is disengaged by computer12and engine22runs at a slower or idle speed sufficient to provide power to accessory devices such as the air conditioning compressor and the power steering pump, and a second or high power mode of operation where clutch38is engaged and engine22operates at a higher speed driving generator40in addition to accessory devices. In the high power mode of operation, engine22will run at a speed designed for optimal efficiency of engine22given the various design parameters and desired output shaft speed for engine22. Gasoline, propane, natural gas, hydrogen or diesel based internal combustion engines may be implemented for engine22, diesel fuel being perhaps the more economical option at the present time. A similar design consideration is implemented for generator40in that generator40is optimized to run at the optimal efficiency speed of engine22, thereby maximizing efficiency in the generation of power while conserving fuel usage by internal combustion engine22.

The use of a variable resistor is contemplated as the source of the signal supplied to computer12by accelerator26. Relays32and34are mutually exclusive in operation, that is, only one of the two relays is energized at any moment in time to isolate the output of both high power batteries from each other. Mutually exclusive operation can be achieved by the use of two relays as shown, by using a double-pole-double-throw relay or by electronic circuits that prevent relay32and relay34from being simultaneously energized. Another mechanism also contemplated is a relay having two sets of contacts, one normally open and one normally closed, with break before make operation useful to switch the two battery outputs to the motor drive circuit16. Considerations for safety of operation in the software executed by computer12will serve to minimize the risk of fire in the event of a system component failure or as a result of a moving vehicle accident that causes damage to system components.

During normal operation of vehicle10, the active or “online” battery, i.e., the battery (either battery32or34) that is currently electrically connected to drive circuit16via either relay28or30, will discharge as power is consumed by drive motor18. For example, assume computer12has energized relay28and battery32is currently electrically connected to drive circuit16. When the output of battery32falls below a predetermined voltage thereby indicating battery32is in need of recharging, computer12will de-energize relay28and energize relay30to disconnect battery32and connect battery34to drive circuit16to maintain a power input signal to drive circuit16. Computer12will then command battery charging circuit20to supply a battery charging signal to battery32. When the charge state of battery34has diminished to a level indicating recharging is required, battery34is taken offline by de-energizing relay30and battery32is brought online by energizing relay28. If both batteries32and34are in a low state of charge, computer12will inform the operator via driver display36of the state of the batteries and estimate a driving distance that the vehicle may traverse before all battery power has been drained. Computer12will, in this manner, prevent a driver from being stranded without vehicular locomotion. Alternatively, generator40may be designed to provide a “limp home” power output capability to drive circuit16to supply drive motor18with sufficient power to operate vehicle10at a low rate of speed. The “limp home” mode is achieved by computer12by energizing relay28while simultaneously commanding charging circuit20to output a signal on signal path44sufficient for drive circuit16to actuate drive motor18at a low rate of speed.

Solid state switching devices well known in the electronic arts may be substituted for relays28and32, though high quality relay contacts are typically considered to be preferred high power switching devices as they have negligible power loss across high quality relay contacts.

It is also contemplated that engine22may include a low power alternator or similar charging device for generating electrical power necessary for normal operation of engine22and charging battery48. Another alternative design approach includes removing clutch38to establish a mechanical direct drive between generator40and engine22and utilizing a field current circuit supplied to generator40to vary the mechanical load and corresponding output of generator40. Other enhancements contemplated include deriving a charging signal from motor18during vehicle deceleration or coasting and using the derived charging signal to return some charge to the vehicle batteries.

Referring now toFIG. 2, a flowchart for the computer program executed by vehicle computer12is shown. The computer program executed by computer12begins at step100when switch24is turned on by the operator of vehicle10. Execution continues with step102wherein system initialization take place. Initialization steps include disabling relays28and30, updating driver display36with driver vehicle operational information, setting motor drive circuit16to a startup control state so that no power is delivered to motor18, and initializing battery charging circuitry20to a known state. Other initialization steps include diagnostic testing of data link14for proper communications with all of the devices connected thereto, including engine22, drive circuit16, charging circuitry20and driver display36. Next at step104computer12begins execution of the vehicle operation routine program which is a looping program set forth in more detail inFIG. 3. Next at step106computer12runs the battery charging and accessory routine or program, described in more detail in the embodiments shown inFIGS. 4 and 5. Following step106, computer12checks for power down input from switch24. If power has been turned off by the user, program execution continues at step110where a power down sequence is initiated and engine22is stopped. After step110, program execution ends at step112. If at step108the position of on/off switch24is still in the on or run position, program execution returns to step104.

Referring now toFIG. 3, the vehicle operation routine of step104inFIG. 2is shown in more detail. The vehicle operation routine begins at step120. Following step120at step122, computer12actuates one of the relays28and30(normally open contact relays) so that high voltage battery power from one of the batteries32or34is connected to motor drive circuit16. The decision as to which relay28or30is actuated at step122is based upon the charge state of the batteries. The charge state of batteries32and34is measured or monitored by charging circuit20and corresponding battery charge data is supplied to computer12via data link14. Thus, if battery32has a higher charge state, computer12energizes relay28to connect battery32to drive circuit16, and battery32is now the “online” battery while battery34becomes the “offline” battery. Next at step124computer12tests whether an external power cable has been connected to plug50. Detection of a power cable connected to plug50is accomplished via battery charging circuitry20notifying computer12via data link14of an external power signal detected on signal path51. If external power is detected program execution continues at step126wherein motor drive circuit16is disabled so that drive motor18does not operate and preventing movement of vehicle10when external power is connected. If at step124external power is not detected, then program execution continues at step128wherein computer12monitors the signal from accelerator pedal26and commands motor drive16to output a voltage to drive motor18in accordance with the position of pedal26and current vehicle speed. Following steps128and126, program execution continues at step130. At step130computer12obtains the online battery charge state or charge capacity from charging circuitry20and if the charge state is not below a predetermined value program execution returns to step124. If at step130the online battery charge state is below a predetermined limit program execution continues at step132. At step132computer12obtains the offline battery charge state from charging circuitry20to ensure it is ready for use. If the offline battery charge state is below a predetermined charge state execution continues at step132and a warning message is displayed on drive display36to inform the operator that both batteries have a charge state below a predetermined limit informing the driver that a fixed amount of charge remains and vehicle operation is distance limited. If at step132the offline battery tests above the low charge limit, then program execution continues at step136wherein computer12disconnects the online battery from drive circuit16by disabling the corresponding relay (28or30) and connects the offline battery to motor drive circuit16by energizing the corresponding relay (28or30) to connect the higher charge state battery to drive circuit16. For example, if relay28is currently energized at step132, and battery32has low capacity (as determined at step130) while battery34has an adequate charge state above a predetermined value, then computer12will de-energize relay28and energize relay30at step136to take battery32offline and make battery34the online battery by energizing relay30to connect battery34to drive circuit16. It should be readily understood that the decision making process of computer12in switching batteries online and offline is based on battery charge state with the objective being to switch the batteries between online and offline states when charge state is low for the online battery and charge state is much higher for the offline battery. Following step136, program execution continues at step124wherein computer12continues in this loop to monitor accelerator pedal26signals and command drive circuit16to output power to drive motor18in accordance therewith. Battery charge capacity predetermined limit values are selected to prevent undesirable rapid switching between online and offline batteries, for example, time delays and hysteresis are implemented.

Referring now toFIG. 4, a more detailed flowchart of the battery charging and accessory routine of step106inFIG. 2is shown. The routine shown inFIG. 4is one embodiment for step106andFIG. 5is another embodiment for step106. At step142, following step140, computer12queries charging circuit20regarding external power signal presence, and if an external power signal is detected, program execution loops on step142until external power is disconnected to prevent vehicle damage or damage to external power plug50if the vehicle moves. If external power is not detected at step142, execution continues at step144wherein computer12commands engine22to start. Next at step146, computer12queries battery charging circuitry20as to whether the offline battery requires charging. If the offline battery requires charging then step148is next executed and engine22is commanded to operate at a fully operational speed optimized for fuel usage and engage generator40by enabling clutch38to provide a power signal at path42to charging circuitry20used to charge batteries32and/or34. Computer12instructs charging circuitry20to charge the offline battery by supplying a charging signal to either signal path44or46, depending upon which battery is in the offline state. For example, if battery32is offline, charging circuitry20provides a charging signal at signal path44and if battery34is offline, a battery charging signal is provided at signal path46in accordance with commands from computer12via data link14. Following step148execution continues at step152. If at step146computer12determines the offline battery does not require charging, then program flow continues at step150wherein computer12commands engine22to run at a predetermined idle speed. Following step150, execution continues at step152. At step152, computer12queries charging circuitry20to determine whether offline battery charging is completed. If charging is completed at step152, execution continues at step154wherein computer12commands engine22to disengage generator40by disabling clutch38, and set the speed of engine22to an idle speed so that alternator power is maintained to provide low level electrical power to vehicle10components and charge vehicle systems battery48. Program execution continues at step156following step154. If at step152the offline battery is determined to require further charging, then program execution continues at step156where computer12receives vehicle heating and air conditioning inputs via driver display and control interface36. If passenger compartment cooling is desired by the vehicle operator, computer12commands engine22to engage the A/C compressor at step158. If at step156A/C is not requested by the operator via computer12, computer12commands engine22to disable the A/C compressor at step160. Following steps158and160execution loops back to step142.

Referring now toFIG. 5, another embodiment of the battery charging and accessory routine of step106inFIG. 2, according to the present invention, is shown. The routine begins at step180and continues at step182where computer12tests to determine if external power is connected at power plug50. If external power is detected, execution loops back on step182preventing any further execution of this routine. If at step182external power is not detected, program execution continues at step184where computer12obtains offline battery charge state data from battery charging circuitry20and system battery48charge state data from engine22if either requires charging execution continues with step186. At step186engine22is started by computer12and clutch38is engaged to provide mechanical rotational power to generator40. If battery charging is not required at step184, i.e., both the offline battery and system battery48are above predetermined charge capacity limits, then step188is executed following step184. Next at step188, computer12obtains charge state data for the offline battery from charging circuitry20and the charge state of system battery48from engine22and if both batteries are sufficiently charged above a predetermined full charge capacity, program execution continues at step190wherein computer12disables generator40by disengaging clutch38via commands to engine22. Following step190, execution continues at step192where computer12checks for the operational state of the climate control system of the vehicle10and if the operator has requested cooling of the passenger compartment then program execution continues at step194where computer12will start engine22, if it is not already running, and instruct engine22to engage the A/C compressor to provide cooling of the passenger compartment. If A/C compressor operation has not been requested at step192, then program flow proceeds to step196where computer12commands engine22to disengage the A/C compressor and halt engine22from operating. By halting operation of engine22for periods of time, a higher efficiency of operation is achieved. Following steps194and196program execution continues at step182.

If at step188computer12determines that the offline battery has not been fully charged or the system battery48is not fully charged then program execution continues at step198. If A/C cooling is needed at step198computer12will continue at step200and engage the A/C compressor if the operator has requested cooling of the passenger compartment. If the A/C compressor is not required at step198, then step202is executed and the A/C compressor is disengaged via a command request sent to engine22from computer12. Following steps200and202, program execute returns back to step182.

The primary difference between the routines shown inFIGS. 4 and 5is the periodic halting of engine22in theFIG. 5embodiment when the offline battery and system battery are sufficiently charged. Halting engine22provides an added level of efficiency wherein hydrocarbon fuels used to power engine22are conserved. The embodiment ofFIG. 5preferably includes a vehicle that does not require a power steering assist pump, or alternatively, a power steering assist device that is electrically powered is contemplated. It should be recognized that not every vehicle requires power steering, particularly smaller vehicles, thus the embodiment ofFIG. 5is contemplated as desirable for its additional energy savings.