WO2010023664A1

WO2010023664A1 - Diesel electrical vehicle

Info

Publication number: WO2010023664A1
Application number: PCT/IL2009/000824
Authority: WO
Inventors: Arthur J. Grunwald; Amiram Admon
Original assignee: Technion Research & Development Foundation Ltd.
Priority date: 2008-08-25
Filing date: 2009-08-25
Publication date: 2010-03-04

Abstract

A serial hybrid electric vehicle comprises at least one ultra capacitor as a sole buffer source for buffering energy generated from a generator of the vehicle powered by an ICE as well as energy regenerated from a braking system of the vehicle, and an energy management system for controlling real-time charge level of the ultra-capacitor according to a real-time velocity of the vehicle.

Description

DIESEL ELECTRICAL VEHICLE

FIELD OF THE INVENTION

The present invention relates to serial hybrid electrical vehicles, and more particularly to hybrid electrical vehicles employing Ultra-Capacitors (UC).

BACKGROUND OF THE INVENTION

Hybrid electric vehicles (HEV) combine a conventional internal combustion engine drive system with an electric drive system. A series hybrid electric vehicle (SHEV) is a vehicle with an engine (most typically an Internal Combustion Engine (ICE)), which powers a generator. The generator, in turn, provides electricity for a battery and motor coupled to the drive wheels of the vehicle. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) is a vehicle with an engine (most typically an ICE), battery, and electric motor combined to provide torque to power the wheels of the vehicle. The vehicle braking system can also deliver torque to drive the generator to charge the battery (regenerative braking).

The presence of the electric drive system is intended to achieve better fuel economy than a conventional vehicle. The Hybrid-Electrical vehicle is optimally used in stop-and-go traffic, in which a running ICE is wasteful in particular. Typically, the electrical drive system is powered by a large bank of chemical batteries that are periodically recharged based on a defined energy management system.

U.S. Patent Application No. 20040060751 entitled "Method for Controlling the Operating Characteristics of a Hybrid Electric Vehicle" the contents of which is incorporated herein by reference, describes a control method for operating internal combustion engine electric hybrid vehicles with smaller battery packs. The interaction between the combustion engine and battery operated electric motor is controlled by taking energy into the batteries only if it is more efficient than throttling the engine and operating the engine at a lower efficiency. Additionally, the batteries are charged to a certain state or the batteries are maintained at a particular state of charge. It is noted that the term "battery" can refer to any energy storage device such as an UC, electrochemical battery, or the like. U.S. Patent Application No. 20050 entitled "Method and System of Requesting Engine ON/OFF State in Hybrid Electric Vehicle" the contents of which is incorporated herein by reference, describes a method and system of engine start/stop control for a HEV that monitors the battery and requests a specific engine state based on condition of the battery. A battery parameter such as discharge power limit (DPL) or state of charge (SOC) is compared with a set of threshold levels including a MIN level, an ON level, and an OFF level and the result of the comparison provides inputs to a state machine.

U.S. Patent Application No. 20050228553 entitled "Hybrid Electric Vehicle Energy Management System" the contents of which is incorporated herein by reference, describes an energy management system that controls an energy storage device of a hybrid electric vehicle responsive to an anticipated likely driving pattern, and possibly responsive to information from environment sensors. The anticipated likely driving pattern is determined based on a vehicle location sensor such as a GPS that determines location data for a vehicle that travels from a known first destination to a second destination. In one embodiment, a recuperated turbine engine power generator is shut off in advance of reaching an anticipated destination so as to recover latent heat energy from a regenerator, wherein the recovered energy can be either stored in the energy storage unit or used to drive a traction motor of the hybrid electric vehicle.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present invention there is provided a SHEV that uses UCs as the sole buffer between the generator and the motor and that does not require batteries, e.g. chemical batteries for buffering. According to some embodiments of the present invention, the UC acts as a short term buffer for providing power generated from the ICE and/or regenerated from the braking system to the electric drive system.

According to an additional aspect of some embodiments of the present invention there is provided an energy management system that is particularly geared toward managing the energy level of the UCs for buffering. Some of the advantages of UCs as compared to chemical batteries are that the charge level of an UC can be directly monitored and controlled in real time. A disadvantage of UCs is that they have a much smaller energy density than chemical batteries. However, since the UC is able to charge and discharge quickly, real time control provides for adjusting the charge level on demand. According to some embodiments of the present invention, the energy management system of the present invention takes advantage of the real time controllability of the UC to provide for an energy management system with improved agility that can quickly charge/discharge the UC on demand.

It is noted that one of the advantages of the UC is that it does not suffer from the many environmental issues associated with disposing of batteries. Additionally, the weight of the UC is significantly lighter than a battery when similar power output has to be provided. An aspect of some embodiments of the present invention is the provision of a serial hybrid electric vehicle comprising: at least one ultra capacitor as a sole buffer source for buffering energy generated from a generator of the vehicle powered by an ICE as well as energy regenerated from a braking system of the vehicle; and an energy management system for controlling real-time charge level of the ultra-capacitor according to a real-time velocity of the vehicle.

Optionally, the at least one ultra capacitor has sufficient capacitance to hold energy required to accelerate the vehicle from zero to a defined maximum allowed velocity of the vehicle.

Optionally, the energy management system operates to provide enough energy in the capacitor to accelerate the vehicle to maximum speed and leave enough unfilled capacity to receive all of the energy expected to be received from the wheels if the vehicle is stopped.

Optionally, the at least one ultra capacitor includes a plurality of UC connected in series. Optionally, the vehicle comprises at least one electric motor for driving at least one wheel of the vehicle, wherein the at least one electric motor is intermittently operated as an electric generator for regenerating the braking energy for storage in the UC.

Optionally, excess energy breaking above the maximum capacity of the UC is used to drive the generator of the vehicle, with the ICE of the vehicle acting as an external load. Optionally, the ICE is a Diesel engine and wherein the Diesel engine, without fuel supply operates as an air compressor to dissipate the excess energy through an exhaust of the ICE.

Optionally, the ICE runs within a steady operating range for at least 50% of the time.

Optionally, the ICE runs within a steady operating range for at least 80% of the time.

Optionally, the steady operating range is between 0-20 KWatts.

An aspect of some embodiments of the present invention is the provision of a method for managing an energy level of a UC used for buffering energy in a serial hybrid electric vehicle, the method comprising: determining a velocity of the vehicle; determining energy required to reach a pre-defined maximum velocity from the determined velocity; defining a target energy level of an UC as the determined energy plus a defined minimum energy; and adjusting energy level of the UC based on the defined target energy level.

Optionally, the defined minimum energy is the energy required for traction.

Optionally, the method comprises identifying a driving pattern of the vehicle; and adjusting the target energy level in response to the identifying.

Optionally, the driving pattern is determined only from vehicle based observations.

Optionally, the driving pattern is selected from: urban driving pattern, higher speed driving pattern, prolonged up-slope driving pattern, and prolonged down-slope driving pattern.

Optionally, the method comprises adjusting the defined minimum energy in response to the identifying.

Optionally, the minimum energy is increased in response to identifying a prolonged up slope driving pattern.

Optionally, the adjusting is in response to a command issued to an ICE throttle of the vehicle. Optionally, the ICE runs within a defined operating range for at least 50% of the time. Optionally, the ICE runs within a defined operating range for at least 80% of the time.

Optionally, the defined operating range is between 0-20 KWatts.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings: FIG. 1 is a simplified block diagram of the SHEV in accordance with some embodiments of the present invention;

FIG. 2 is a simplified flow chart of an exemplary operational method of an energy management system in accordance with some embodiments of the present invention; FIG. 3 is a simplified flow chart of an exemplary method for computing a target energy level for an UC in accordance with some embodiments of the present invention;

FIG. 4 is a simplified control scheme for a drive system in accordance with some embodiments of the present invention;

FIGS. 5 A and 5B show a velocity and acceleration profile obtained in an exemplary simulation in accordance with some embodiments of the present invention; FIGS. 6 A and 6B is an expanded time scale of the velocity and acceleration profile shown in FIGS. 5 A and 5B in accordance with some embodiments of the present invention;

FIG. 7 power dissipated by the UC in comparison to power generated by the Diesel generator to obtain velocity profile shown in FIG. 5A in accordance with some embodiments of the present invention;

FIG. 8 is a voltage profile for a UC obtained in the exemplary simulation in accordance with some embodiments of the present invention;

FIG. 9 is an expanded time scale of power dissipated by the UC in comparison to power generated by the Diesel generator as shown in FIG. 7 and in accordance with some embodiments of the present invention;

FIG. 10 is an expanded time scale of a voltage profile for a UC obtained in the exemplary simulation as shown in FIG. 8 and in accordance with some embodiments of the present invention; and FIGS. HA and HB are motor current profiles obtained for the exemplary simulation and in accordance with some embodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention relates to serial hybrid electrical vehicles, and more particularly to serial hybrid electrical vehicles employing UCs.

An aspect of some embodiments of the present invention is the provision of a serial hybrid electrical vehicle using UCs as a sole buffer element for holding charge for powering the electric drive system. The present inventors have found that although UCs are typically associated with lower charge density as compared to chemical batteries, they can deliver high power over a short time span due to its fast (almost instantaneous) charge and discharge rate. This characteristic is particularly suitable for stop-and-go traffic where a vehicle alternates between acceleration and decelerations over short time spans.

According to some embodiments of the present invention, the UC(s) has sufficient capacitance to hold energy required to accelerate the vehicle from zero to maximum allowed velocity. Typically, the weight of an UC that is able to accelerate the vehicle from zero to maximum velocity is significantly lighter, e.g. four times lighter, than the weight of chemical batteries required for achieving a similar performance. According to some embodiments of the present invention, the energy stored in the UC provides delivering power surges when required while the ICE is typically operated at steady operating conditions, e.g. between a defined operating range. According to some embodiments of the present invention, the generator is a Diesel electric generator or any other fuel efficient power supply. Diesel electric generators are known to be fuel efficient when operated at defined operating conditions, e.g. at a give rotational speed and torque.

In contrast to chemical batteries, the UC has an almost unlimited lifespan and eliminates the need for large scale recycling. Moreover, the UC is able to provide a very high electrical current in a short time, which facilitates agile driving.

According to some embodiments of the present invention energy is regenerated during braking by allowing the electric wheel motors to act as electric generators and thereby avoid the use of mechanical brakes. The high charge rate of the UCs provides for harnessing most if not all of the regenerated energy during braking. Known hybrid vehicles employ UCs specifically for temporarily storing energy regenerated during braking until the charge can be used to recharge the associated battery.

Since the electrical energy storage capacity is limited, a dedicated energy management scheme is required to adjust the charge level of the UC in real time such that sufficient energy is available when needed for the current driving situation, and sufficient storage capacity available to regenerate the braking energy. In other words, the charging level of the capacitor is such that there is enough energy in the capacitor to accelerate the vehicle to maximum speed and enough unfilled capacity to receive all of the energy expected to be received from the wheels if the vehicle is stopped. Adjustments to the energy management scheme is made for different driving patterns, e.g. to compensate for power requirements or conditions during up and down slope driving over prolonged periods. According to some embodiments of the present invention, driving patterns are learned and/or predicted based on vehicle based observation, e.g. vehicle velocity, vehicle acceleration, traction torque, UC energy level, and vehicle slope angle.

Known battery-based energy management schemes are not suitable in this respect as their charging strategy has to take in to account the slow charge and discharge rate of the batteries, e.g. chemical batteries as well as parameters that can affect the life span of the batteries. Additionally, the available charge level of the battery is not easily monitored and controlled as compared to UCs.

An aspect of some embodiments of the present invention is the provision of an energy management system for managing energy of the SHEV as described herein that directly controls the energy level of the UC in real time. In some exemplary embodiments, the energy management system uses vehicle and/or environmental sensed parameters tracked over short time periods, e.g. over periods of 5 minutes, to adjust energy levels of the UC. According to some embodiments of the present invention, the charge level of the

UC is directly controlled by a current velocity of the vehicle. In some exemplary embodiments, the ability of the UC to alter its discharge and charge level in real-time to accommodate fast changes in power requirements enables to ICE generator to run at steady conditions while peak changes in power are managed by adjusted energy levels of the UC. The present inventors have found that the high agility of the energy management system provides for improved harnessing of regenerated energy during fast changes in velocity that is typical in stop-and-go traffic. Drive System

Reference is now made to FIG. 1 showing a simplified block diagram of a drive system in accordance with some embodiments of the present invention. According to some embodiments of the present invention, drive system 100 uses four electric motors 115 to deliver torque to wheels 105 via drive shafts 107. Optionally, three or fewer electric motors are used, e.g. one motor is used to drive two front wheels for a front wheel drive vehicle. According to some embodiments of the present invention, current to motors 115 are supplied by one or more UCs 110 which temporarily buffers charge received by a generator 120 and energy regenerated during braking. Typically, generator 120 is powered by an ICE 130, e.g. a Diesel engine. In some exemplary embodiments, a servo controller 140 regulates electric current flow between UC 110 and each of motors 115. Typically, current to the electric motors are provided by a plurality of UCs, e.g. arranged in series to form a UC pack. According to some embodiments of the present invention, UC 110 pack has sufficient capacitance to hold the energy needed to accelerate a vehicle from zero to the maximum allowed velocity. Likewise, the capacitance is sufficient to recapture energy regenerated during braking by electrical rather than mechanical braking. Optionally, the capacitance of the UC pack ranges between 10-50 Farads. Optionally, the UC pack provides for a bus voltage of between 200-600 VDC that yields currents of between 200-800 Amps.

According to some embodiments of the present invention, during braking, electric motors 115 are used as electric generators to charge UC 110. In such a manner, braking energy is regenerated and mechanical brakes can be avoided. In some exemplary embodiments, when the UC reaches maximum charge, excess energy produced by the wheel motors is used to drive generator 120, with ICE 130 acting as an external load. Optionally, when a Diesel engine is used, ICE 130 without fuel intake will act as an air compressor and the energy produced will dissipate through the exhaust.

In some exemplary embodiments, drive system 100 includes auxiliary mechanical brakes for safety and for cases when the load of the ICE is insufficient. Typically, the auxiliary mechanical brakes will be smaller than those used in conventional ICE vehicles. Optionally, ICE 130 is left to idle and the excess electrical energy is dissipated in braking resistors.

According to some embodiments of the present invention, an energy management system 150 issue commands to both servo controller 140 and ICE throttle 130 based on inputs from an energy sensor 170, vehicle state sensors 160, and vehicle controls 180. In response to issued commands, UC 110 is discharged by servo-controller 140 and/or charged by ICE generated energy. Optionally, in response to issued commands, e.g. during braking, UC 110 is charged by servo-controller 140. Typically, energy sensor 170 tracks the voltage level of UC 110, e.g. with a volt meter and vehicle state sensors 160 track various vehicle kinetics, e.g. velocity, acceleration/deceleration and traction torque of the vehicle. Typically, the input from vehicle control includes driver commands, e.g. in response to pressing brakes and/or the accelerator. Optionally, environmental sensors, e.g. temperature sensors and/or inclination sensors serve as additional inputs to energy management system 150. Energy Management System

According to some embodiments of the present invention, input to energy management system 150 is obtained in real-time and/or is updated continuously at sampling rates of at least 0.1 seconds. The inputs are stored in a running window with a time span of 30-200 seconds, e.g. as new measurements enter the window, old ones are pushed out. The data in the window are continuously processed to allow the energy management system 150 to effectively respond to fast changes in vehicle kinetics by matching the energy level of the UC to real time power requirements of the vehicle while also leaving enough unfilled capacity to harness regenerated energy on the other hand.

Reference is now made to FIG. 2 showing a simplified flow chart of an exemplary operational method of an energy management system in accordance with some embodiments of the present invention. According to some embodiments of the present invention energy management system 150 receives monitors input received from drive system 100 (block 201). In some exemplary embodiments, monitored inputs include inputs from vehicle state sensors 160, vehicle controls 180, e.g. driver commanded velocity, and energy measurement sensors 170 to monitor energy and/or charge level of UC 110. Typically, inputs from vehicle state sensors 160 include current readings of velocity, acceleration and traction torque of the vehicle.

According to some embodiments of the present invention, energy management system 150 learns a driving pattern based on the monitored inputs (block 202). In some exemplary embodiments, the driving pattern is determined over short time spans, e.g. time spans ranging between 2-5 minutes. Based on the learned driving pattern, a control scheme is defined (block 203). In some exemplary embodiments, energy management system 150 selects a control scheme from a number of pre-defined control schemes suitable for different driving patterns. Exemplary driving patterns include urban low speed driving, prolonged up-slope driving, prolonged down-slope driving, and high speed driving. According to some embodiments of the present invention, based on the control scheme defined, energy management system issues commands to servo controller 140 (block 204) and issues power commands to ICE 130 (block 205). The issued commands control the energy flow to and from UC 110.

According to some embodiments of the present invention, the energy level of the UC is maintained between a defined high and a defined low level of energy. According to some embodiments of the present invention, energy management system 150 computes (and updates in real time) a target energy level for UC 110 between the defined high and low energy level and compares the computed target level to the actual energy level of the capacitor. In case of discrepancies, a power command to the generator is adjusted and/or issued so that the energy level of UC can be appropriately adjusted. Urban Driving Pattern

Typically urban driving is characterized by low to medium speed driving with frequent stops. Top power demands are seldom long-lasting in urban driving and when they occur the are followed by periods of low power demands or even situations in which the energy can be regenerated during braking by allowing the electric wheel motors to act as electric generators, and avoid the use of mechanical brakes.

According to some exemplary embodiments, when an urban driving pattern is identified, the energy management system is geared toward continuously adjusting target energy level of the UC that it may harness all the regenerated power from breaking but still have enough charge to accelerate and for traction. Reference is gain made to FIG. 2 showing a simplified flow chart of an exemplary method for computing a target energy level for an UC in accordance with some embodiments of the present invention. According to some embodiments of the present invention, the method described in reference to FIG. 2 is particularly suitable for urban driving characterized by medium to low speed driving with frequent stops. According to some embodiments of the present invention, the current velocity of the vehicle is monitored (block 210) from vehicle state sensors 160 and is input to energy management system 150. In some exemplary embodiments, based on a current velocity, the energy required to accelerate the vehicle from its current velocity to the maximum velocity of the vehicle is computed (block 220). Typically, the electrical and mechanical efficiency is also taken into account when computing the required energy.

According to some embodiments of the present invention, the dynamic range of the energy level of the UC, e.g. the low and high energy level is defined (block 230). In some exemplary embodiments, the high level is defined as the maximum charge that the UC can accumulate and the low energy level is defined as the minimum energy required for potential necessary changes in the equilibrium vehicle state, like acceleration, changes in rolling and air resistance and changes in the slope angle. The summation of the low energy level and the energy required to accelerate the vehicle from its current velocity to the maximum velocity is checked against the defined high energy level of the UC (block 240).

According to some embodiments of the present invention, if the summation is less than the defined high value, the target level is defined as the low level energy plus the energy needed to accelerate the vehicle from the present velocity to the maximum velocity (block 250). Otherwise, the target level is defined as the high level of the UC (block 260). When adopting this strategy, the UC will be fully charged at rest and will be charged at the low level at top speed. Fully charging the UC at rest provides maximum power to accelerate the vehicle from a rest stage, while reducing the charge of the UC at top speeds leaves unfilled capacity for harnessing regenerated power in response to braking.

According to some embodiments of the present invention, the ICE engine is run at a steady operating condition and/or a defined operating range, e.g. 0-50 KWatts and is typically not required to provide large power surges. The large power surges required for example in urban driving are typically provided by energy stored and dissipated by the UC. Higher Speed Driving Pattern

In some exemplary embodiments, when driving in congested interstate traffic where speed variations occur at higher speeds and with no or few anticipated complete stops, the target energy level as computed by FIG. 2 may be to be low due to the lower electrical efficiency at lower UC energy levels. In some exemplary embodiments, when such a driving pattern is recognized, driving statistics over a given time span are analyzed and adjustments to the defined target energy level computed in FIG. 2 are made based on the analysis. Optionally, the velocity pattern over a defined time span, e.g. 2-7 minutes, and the energy level of the UC are monitored and used to compute the adjustments to a computed target energy level.

Alternatively, when driving at the maximum speed, the target energy level of the UC is maintained at a constant level and the ICE is typically operated at high or maximum output power. Typically, all the generated power will be used to overcome the air and rolling resistance of the vehicle. The maximum speed of the vehicle is limited by the output of the ICE. When driving at maximum speed, the fuel economy of the electrical drive system will typically be no better than conventional drive systems. According to some embodiments of the present invention, when the vehicle is driving on a highway at constant speed, the UC is in equilibrium, e.g. the energy that is dissipated and the energy that is generated are equal. For high driving at constant speed, the ICE will typically delivers exactly the energy that is needed to keep the vehicle going and the voltage level of the UC is maintained at a constant value. Prolonged Up-slope Driving Pattern

In some exemplary embodiments, when a prolonged up-slope is identified, energy management system operates to maintain the energy level of the UC constant and the velocity of the vehicle is determined by the ICE output power. This control scheme is particularly suitable in cases when all the energy from the Diesel engine is needed for the climb. In some exemplary embodiments, for steeper slopes, the speed of the vehicle may drop to boost the power required for the climb. This may analogous to shifting to a lower gear on a climb. Prolonged Down-slope Driving Pattern Typically, energy management system 150 operates to maximize harnessing of regenerated energy. However, during prolonged down-slope driving UC may reach its upper limit during while the vehicle is continue on its down-slope path. In some exemplary embodiments, in response to excess regenerated energy, energy management system 150 issues a command to servo controller 140 to direct the excess energy produced by the wheel motors (acting as generators) to drive the generator with the ICE as an external load. In such a case, the ICE, e.g. the Diesel engine, without fuel supply, will act as an air compressor and the energy of which will disappear through the exhaust. Optionally or additionally, energy management system may issue a command to use auxiliary mechanical brakes and/or to dissipate the excess electrical energy in braking resistors.

Drive System Control

Reference is now made to FIG. 4 showing a simplified control scheme for a drive system in accordance with some embodiments of the present invention. According to some embodiments of the present invention, driving system control is initiated with a speed command (1) originating from the driver controls 180. Speed command (1) together with actual speed (2) is used by a speed controller 185 to compute the required acceleration or deceleration forces (3). Optionally, a slope angle sensor 410 senses vehicle slope 406 and the forces for moving on a slope (5) together with a computed air and rolling resistance (4) are used to determine a required traction force (6).

Typically, required traction force (6) along with the electrical and mechanical efficiency (7) is used to determine a required electrical power (8) to electric motors 115 (FIG. 1) to execute speed command (1).

According to some embodiments of the present invention, the amount of electrical power that can be delivered to the electric motors depends on the energy level of UC (12). According to some embodiments of the present invention, the available electric power is computed (block 420) and the actually dissipated or regenerated electrical power (9), e.g. the stored electrical energy is translated into available traction torque (18) which is computed (block 440). The provided traction torque (18) together with vehicle dynamics results in the acceleration/deceleration of the vehicle leading to an updated velocity. According to some embodiments of the present invention, vehicle state sensor 160 monitors the acceleration and velocity of the vehicle. Typically, vehicle state sensor 160 additionally monitors the traction torque of the vehicle.

According to some embodiments of the present invention, the energy balance (11) to the UC consists of the dissipated/regenerated power (9) and the electrical power produced by generator 120 (10). Typically, when balance (11) is positive, the UC will be charged, otherwise it will be discharged. Integration of the balance (11) over time yields the energy level of the UC (12) which is monitored by energy sensor 170.

According to some embodiments of the present invention, at times the energy flow from the generator will be inverted, e.g. over prolonged down slopes. In some exemplary embodiments, in such a case, the UC delivers power to the generator, which acts as an electromotor driving the ICE, e.g. Diesel engine. In some exemplary embodiments, the Diesel engine, without fuel supply, functions as an air brake or auxiliary braking, as described above, is used.

According to some embodiments of the present invention, the energy management system 150 operates to maintain the energy level of the UC (12) at the computed target level (13). The target level is computed by the energy management scheme (block 470). In some exemplary embodiments, while the energy level is at the target level, the UC is able to accumulate regenerated braking energy as well as deliver energy for traction. According to some embodiments, when the energy level of the UC (12) strays from the computed target level (13), the difference (14) is passed through a controller gain 439 to produce a power signal (15). According to some embodiments of the present invention, a computed power needed to overcome air and rolling resistance (16) is added to power signal (16) to obtain the power signal used to issue command (17) to ICE throttle 130. Exemplary Simulation

A simulation study was carried out in which the control scheme described in reference to FIG. 4 was implemented in a Simulink ® simulation from MathWorks ™. Reference is now made to FIGS. 5 A and 5B showing a velocity and acceleration profile obtained in an exemplary simulation in accordance with some embodiments of the present invention. In the simulation depicted, a 1000 kg passenger car was driven according to the commanded speed profile 510 over a time span of 450 seconds. FIGS. 6 A and 6B shows the first 100 seconds in an expanded time scale. As can be seen in the expanded time scale, an initial acceleration of 2 m/sec² yields a velocity of 20 m/sec and a subsequent acceleration of 1 m/sec² brings the vehicle to a velocity of 35 m/sec. The vehicle decelerates after 60, 80 and 90 seconds to come to rest after 100 seconds. Subsequent intervals of 100 seconds show a varied pattern of high speed and low speed driving, where at 200, 250 and 300 seconds the commanded speed of 40 m/sec is above the maximum speed of the vehicle.

Between 300 and 400 seconds the commanded speed is kept at 40 m/sec and the speed of the vehicle increases above and then stabilizes at 34 m/seconds, the speed for which the air and rolling resistance equals the available traction forces from the ICE.

The simulation used two UC of type Maxwell HTM Power Series 125 Volt positioned in series, yielding a total capacitance of 31.1 Farad at 250 Volts was used. The combined weight of these capacitors is 116 kg and each capacitor is of dimension 762 x 425 x 265 mm. They allow a maximum current of 750 Amperes. The generator used for charging the UC was simulated as a 20 KWatt Diesel generator.

Reference is now made to FIG. 7 showing power dissipated by the UC in comparison to power generated by the Diesel generator to obtain velocity profile shown in FIG. 5A. As shown in FIG. 7, power requirements 710 based on the velocity profile of FIG. 5 A yields power requirements of up to 120 KWatts as well as decelerations that require dissipation of power levels of up to 100 KWatts. Such an energy balance may be typical for a standard passenger car with a gasoline engine of 110 Hp and fitted with disk brakes for dissipating the energy.

Fig. 7 also shows the electrical power 720 generated by the Diesel generator, for this velocity profile. As can be seen, the large power fluctuations typical for gasoline- powered passenger cars are reflected in the fluctuations of the UC dissipated power and not in the generator power. The generator power 720 is kept almost constant at its operating 20 KWatt level. This is a result of the implementation of control strategy as described herein. FIG. 8 shows fluctuations in the UC voltage as a result of the control strategy.

The voltage between around 220-240 seconds is the lowest which corresponds to when the velocity (FIG. 5A) is high. This confirms that the UC does not have to be fully charged when the kinetic energy of the vehicle is high.

FIG. 9 shows the power balance and FIG. 10 the UC voltage for the first 100 seconds time span. Recharging of the UC by regenerated braking energy can be seen after 60 seconds and after 80 seconds (FIG. 10). The braking power is seen by the negative value of the electrical power (FIG. 9).

FIGS. HA and HB show the motor current obtained for the exemplary simulation and in accordance with some embodiments of the present invention. A negative current depicts braking and a positive current positive traction. Between 300 and 400 seconds, when the vehicle is pushed at its maximum speed of 40 m/sec and settled at 34 m/sec (FIG. 5A), the generator settles at a 20 KWatt level and the motor current settles at 180 Amperes which is used to overcome air and rolling resistance. Over, this period, the UC voltage (FIG. 8) settles at its lowest level of 140 volts. According to some embodiments of the present invention, the low energy level of

140 Volts is acceptable for urban driving with frequent braking stops but too low when a full braking stop is not anticipated, e.g. prolonged high-speed driving. Although, the control scheme for prolonged high-speed driving has not been implemented in this exemplary simulation, typically, the energy management system as described herein would identify a prolonged high speed driving patter and accordingly raise the target energy level of the UC. It is noted that a battery for starting the ICE and for powering electrical devices in the car is required. However, such batteries are typically of a different scale and configuration than batteries used for storing energy for driving.

Comparison between an UC based system and a potential battery based system

Table 1 summarizes the weight and volume saving characteristics of a UC based system as described herein, as well as its durability as compared to an exemplary corresponding chemical battery based system. For the purpose of comparison, exemplary off-the-shelf available components, e.g. from Maxwell technologies and from Schnapp have been used. Although the Schnapp battery is not typically used in operation of known hybrid vehicles, it is a low-cost automotive lead-acid battery with is considered to be very robust in terms of its ability to be charged and discharged such as is required by the UC based system. They are designed for providing large power surges when you crank the engine. Parameters listed in Table 1 are based on a power usage of 100 KWatt over a 10 seconds time period. In this example, the system is likewise required a lOOKWatt ability to regenerate power from braking. A bus voltage of 400 VDC yielding currents of 250 Amperes is assumed.

For the comparison, 9 UC of 48.6 Volt and a capacitance of 165 Farad, each is chosen. They are connected in series to yield a bus voltage of 437.4 VDC. This yields an overall capacitance of 18.3 Farad. The total weight is 128 kg and the total volume 113 liters.

For the corresponding battery-based system 33 units of 12 VDC batteries with 250 Amperes cold start. They yield a bus voltage of 396 VDC. The total weight of these batteries is 415 kg and the total volume is 210 liters. The weight and size of the batteries is significantly greater than that of the UC.

When comparing the characteristics of the UC based and the battery based system one has to consider that batteries cannot be recharged at the same rate as they are charged. A general a rule of thumb is that the recharging current is about 25% of the charging current. This means that only 25 KWatt of the braking energy can be retrieved and the rest has to be dissipated either mechanically or in braking resistors.

The UC show a practically unlimited duty cycle, rated at 1 million charging/discharging cycles. In contrast, batteries are known to suffer from the intensive charging and recharging cycles. If the lifetime of a car battery, used for occasional starting of the engine is rated at three years, a battery, performing the above mentioned cycles, is estimated to last less than a year.

One known hybrid vehicle is the Toyota Prius Hybrid whose battery characteristics are described in website http://www.hybridcars.com/hybrid-car-battery downloaded on August 25, 2009 and which is hereby incorporated by reference. The Toyota Prius Hybrid as described consists of 28 Panasonic prismatic nickel metal hydride modules each containing six 1.2 volt cells connected in series to produce a nominal voltage of 201.6 volts. The total number of cells is 168, compared with 228 cells packaged in 38 modules in the first generation Prius. The pack is positioned behind the back seat. The weight of the complete battery pack is 53.3 kg. The discharge power capability of the Prius pack is about 20 kW at 50 percent state-of-charge. The power capability increases with higher temperatures and decreases at lower temperatures. The Prius has a computer that's solely dedicated to keeping the Prius battery at the optimum temperature and optimum charge level. The Prius supplies conditioned air from the cabin as thermal management for cooling the batteries. The air is drawn by a 12-volt blower installed above the driver's side rear tire well.

Toyota Prius battery pack as well as other similar battery packs are typically geared towards energy density and seek the smallest weight and/or volume for the amount of stored energy. Toyota Prius battery pack weights about 50 Kg. The battery pack is not meant for providing large power surges like the 100 KWatt to provide power for the complete acceleration profile. Therefore you cannot accelerate with the Prius on the battery only. An ICE will kick in to provide power surges when required.

To compare a battery of the type used by the Prius would be to the UC as describe herein, the unit would have to output 100 KWatts of power. 100 KWatts may be achieved by using 5 of these double units in parallel leading to a weight of 250 Kg.

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to".

The term "consisting of means "including and limited to". The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features. of those embodiments, unless the embodiment is inoperative without those elements.

Claims

WHAT IS CLAIMED IS:

1. A serial hybrid electric vehicle comprising: at least one ultra capacitor as a sole buffer source for buffering energy generated from a generator of the vehicle powered by an ICE as well as energy regenerated from a braking system of the vehicle; and an energy management system for controlling real-time charge level of the ultra- capacitor according to a real-time velocity of the vehicle.

2. The vehicle according to claim 1, wherein the at least one ultra capacitor has sufficient capacitance to hold energy required to accelerate the vehicle from zero to a defined maximum allowed velocity of the vehicle.

3. The vehicle according to claim 1 or claim 2, wherein the energy management system operates to provide enough energy in the capacitor to accelerate the vehicle to maximum speed and leave enough unfilled capacity to receive all of the energy expected to be received from the wheels if the vehicle is stopped.

4. The vehicle according to any of claims 1-3, wherein the at least one ultra capacitor includes a plurality of UC connected in series.

5. The vehicle according to any of claims 1-4, comprising at least one electric motor for driving at least one wheel of the vehicle, wherein the at least one electric motor is intermittently operated as an electric generator for regenerating the braking energy for storage in the UC.

6. The vehicle according to claim 5, wherein excess energy breaking above the maximum capacity of the UC is used to drive the generator of the vehicle, with the ICE of the vehicle acting as an external load.

7. The vehicle according to claim 6 wherein, the ICE is a Diesel engine and wherein the Diesel engine, without fuel supply operates as an air compressor to dissipate the excess energy through an exhaust of the ICE.

8. The vehicle according to any of claims 1-7, wherein the ICE runs within a steady operating range for at least 50% of the time.

9. The vehicle according to any of claims 1-8, wherein the ICE runs within a steady operating range for at least 80% of the time.

10. The vehicle according to claim 8 or claim 9, wherein the steady operating range is between 0-20 KWatts.

11. A method for managing an energy level of a UC used for buffering energy in a serial hybrid electric vehicle, the method comprising: determining a velocity of the vehicle; determining energy required to reach a pre-defined maximum velocity from the determined velocity; defining a target energy level of an UC as the determined energy plus a defined minimum energy; and adjusting energy level of the UC based on the defined target energy level.

12. The method according to claim 11, wherein the defined minimum energy is the energy required for traction.

13. The method according to claim 11 or claim 12, comprising: identifying a driving pattern of the vehicle; and adjusting the target energy level in response to the identifying.

14. The method according to claim 13, wherein the driving pattern is determined only from vehicle based observations.

15. The method according to claim 13 or claim 14, wherein the driving pattern is selected from: urban driving pattern, higher speed driving pattern, prolonged up-slope driving pattern, and prolonged down-slope driving pattern.

16. The method according to any of claims 13-15, comprising adjusting the defined minimum energy in response to the identifying.

17. The method according to claim 16, wherein the minimum energy is increased in response to identifying a prolonged up slope driving pattern.

18. The method according to any of claims 11-17, wherein the adjusting is in response to a command issued to an ICE throttle of the vehicle.

19. The method according to claim 18, wherein the ICE runs within a defined operating range for at least 50% of the time.

20. The method according to claim 18 or claim 19, Wherein the ICE runs within a defined operating range for at least 80% of the time.

21. The method according to any of claims 18-20, wherein the defined operating range is between 0-20 KWatts.