CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61/539,139, filed September 26, 2011 , which is hereby incorporated by reference in its entirety.

FIELD

[0002] This disclosure relates to vehicles that are powered by an electric traction motor that also include a range extender such as an internal combustion engine.

BACKGROUND

[0003] Electric vehicles offer the promise of powered transportation through the use of electric traction motors and an on-board battery pack while producing few or no emissions. Some electric vehicles include one or more electric motors and an internal combustion engine, which may, for example, be used to assist the electric motor in driving the wheels or to charge the on-board battery pack. [0004] Such vehicles may permit a user to adjust parameters relating to the performance of the vehicle (such as the aggressiveness of the regenerative braking system), but these vehicles still rely on only one control strategy for using the range extender to recharge the battery pack. Additionally, the control strategy that such vehicles rely on may handle one type of situation relatively well, but would not perform ideally in other types of situations.

SUMMARY

[0005] In an aspect, an electric vehicle is provided that is capable of operating according to more than one control model (which may also be referred to as a control strategy) for controlling the state of charge of a battery pack on board the vehicle.

[0006] In a particular embodiment, the vehicle includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, the aforementioned battery pack, which may be configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a first state of charge,

b) charge the battery pack using the range extender system from the first state of charge to a second state of charge that is higher than the first state of charge but that is lower than the fully charged state of charge, and

c) permit depletion of the battery pack from the second state of charge. The control system is further configured to control the state of charge of the battery pack using the range extender system according to a second control strategy that is different than the first control strategy. The control system is configured to apply the first control strategy or the second strategy based on a control strategy input received from an input source.

[0007] In another aspect, a method of operating an electric vehicle having an electric traction motor, a battery pack configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor and a range extender system configured to generate electrical power from a fuel source. The method includes: a) permitting depletion of the battery pack from a fully charged state of charge to a first state of charge,

b) charging the battery pack using the range extender system from the first state of charge to a second state of charge that is higher than the first state of charge but that is lower than the fully charged state of charge, and

c) permitting depletion of the battery pack from the second state of charge. The control system is configured to control the state of charge of the battery pack using the range extender system according to a second control strategy that is different than the first control strategy. The control system is configured to apply the first control strategy or the second strategy based on a control strategy input received from an input source.

[0008] In yet another aspect, an electric vehicle is provided that includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, a battery pack that is configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a first state of charge, b) charge the battery pack using the range extender system from the first state of charge to a second state of charge in which the battery pack is substantially fully charged, and c) permit depletion of the battery pack from the second state of charge.

[0009] In yet another aspect, a method of operating a control system for an electric vehicle is provided. The method includes the aforementioned steps a), b) and c).

[0010] In yet another aspect, an electric vehicle is provided that includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, a battery pack that is configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a first state of charge, b) charge the battery pack using the range extender system from the first state of charge to a second state of charge,

c) permit depletion of the battery pack from the second state of charge to a third state of charge that is higher than the first state of charge, and

d) charge the battery pack using the range extender system from the third state of charge to a fourth state of charge.

[0011] In yet another aspect, a method of operating a control system for an electric vehicle is provided. The method includes the aforementioned steps a), b), c) and d).

[0012] In yet another aspect, an electric vehicle is provided that includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, a battery pack that is configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a first state of charge, b) charge the battery pack using the range extender system from the first state of charge to a second state of charge, c) permit depletion of the battery pack from the second state of charge to a third state of charge, and d) charge the battery pack using the range extender system from the third state of charge to a fourth state of charge that is lower than the second state of charge.

[0013] In yet another aspect, a method of operating a control system for an electric vehicle is provided. The method includes the aforementioned steps a), b), c) and d).

[0014] In yet another aspect, an electric vehicle is provided that includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, a battery pack that is configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a first state of charge, b) charge the battery pack using the range extender system from the first state of charge to a second state of charge, and c) permit depletion of the battery pack from the second state of charge. The first and second states of charge are selectable by a user via an input device.

[0015] In yet another aspect, a method of operating a control system for an electric vehicle is provided. The method includes the aforementioned steps a), b) and c).

[0016] In yet another aspect, an electric vehicle is provided that includes a vehicle body having a plurality of wheels, an electric traction motor operatively connected to at least one of the wheels, a battery pack that is configured for storing electrical energy that is transmissible to the electric traction motor for powering the electric traction motor, and a range extender system that is configured to generate electrical power from a fuel source, and a control system. The control system is configured to determine the state of charge of the battery pack, and is configured to control the state of charge of the battery pack using the range extender system according to a first control strategy in which the control system is configured to a) permit depletion of the battery pack from a fully charged state of charge to a third state of charge,

b) charge the battery pack using the range extender system from the third state of charge to a fourth state of charge,

c) permit depletion of the battery pack from the fourth state of charge to a fifth state of charge, and

d) charge the battery pack using the range extender system from the fifth state of charge to a sixth state of charge that is higher than the fourth state of charge.

[0017] In yet another aspect, a method of operating a control system for an electric vehicle is provided. The method includes the aforementioned steps a), b), c) and d).

[0018] In any of the methods and vehicles described above, the range extender system may include an internal combustion engine and may further include a generator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments will now be described, by way of example only, with reference to the attached drawings, in which: [0020] Figure 1 is a side elevation view of an electric vehicle that includes a range extender system; [0021] Figure 2 is a schematic illustration of a control system for the vehicle shown in Figure 1 , connected to several components in the vehicle; and

[0022] Figures 3-14 illustrate different control strategies for controlling the state of charge of a battery pack in the vehicle shown in Figure . DETAILED DESCRIPTION

[0023] In this specification and in the claims, the use of the article "a", "an", or "the" in reference to an item is not intended to exclude the possibility of including a plurality of the item in some embodiments. It will be apparent to one skilled in the art in at least some instances in this specification and the attached claims that it would be possible to include a plurality of the item in at least some embodiments.

[0024] Figure 1 depicts an electric vehicle 10. The term 'electric vehicle' as used herein denotes a vehicle that includes an electric traction motor 12 (which may be referred to simply as an 'electric motor' for convenience). The electric vehicle 10 may be any suitable type of vehicle, such as, for example, an automobile, a truck, an SUV, a bus, a van, a motorcycle or any other type of vehicle.

[0025] The electric traction motor 12 may be a high-voltage AC motor. The electric traction motor 12 may be mounted in a compartment located forward of a passenger cabin 13 or at another suitable location. The vehicle 10 includes a body 14 and a plurality of wheels 16. The electric traction motor 12 is operatively connected to at least one of the wheels 16 to drive the at least one of the wheels 16. A battery pack 18 is provided and is configured for storing electrical energy that is transmissible from the battery pack to the electric traction motor for powering the electric traction motor. The battery pack 18 may include any suitable number of cells and may operate using any suitable chemistry. For example, the battery pack 18 may be made up of lithium polymer cells. Referring to Figure 2, the battery 18 may be connectable to an external electrical source (not shown) via a charger 20, so as to permit charging of the battery pack 18 when the vehicle 10 is parked. An inverter 22 is provided for converting the direct current received from the battery pack 18 to alternating current for use by the motor 12. In Figure 2, solid connecting lines between elements are intended to illustrate connections where high-voltage current is sent between the connected elements (in some cases the current may flow either way between connected elements depending on circumstances), and dashed lines illustrate where signals and the like are sent between the connected elements (in some cases, the signals may be sent in either direction between connected elements). Some connections between elements may have been omitted for the sake of clarity.

[0026] A control system 24 is provided and includes a processor 25 and a memory 26 that stores data relating to the statuses of a plurality of components, and also stores any software that is run by the processor 24. The control system 24 controls the transmission of electrical power from the battery pack 18 to the inverter 20 and thus to the motor 12. While the control system 24 has been shown in Figure 2 as a single block, it will be understood by persons skilled in the art that in practice the control system 24 may be a complex distributed control system having multiple individual controllers connected to one another over a communications area network. For example, the control system 24 may include a powertrain control module and a transmission control module (which are not shown individually in the figures). The powertrain control module is responsible for, among other things, operation of the motor 12, the battery pack 8 and the vehicle's thermal management system (not shown, but which is responsible for cooling the motor 12, the battery pack 18 and other components). The transmission control module may be mounted with the inverter 20 and is separate from the powertrain control module, and carries out commands received from the powertrain control module to increase or decrease the amount of current being sent to the motor 12.

[0027] The control system 24 is connected to several components such as the motor 12, the inverter 22 and the battery pack 18. The control system 24 may receive signals from those components or from sensors mounted at those components so as to determine the states of those components. Such signals may include indications of the amount of current being drawn from the component, the temperature of the component, the speed of the component, or signals relating to any other suitable parameter. Additionally or alternatively, the control system 24 may control the operation of those components. The signals between the control system 24 and the components may be controller- area network bus (CAN bus) or the like.

[0028] The control system 24 may also be connected to an accelerator pedal shown at 27 and a brake pedal shown at 28, so the position of each pedal 26 and 28 is communicated to the control system 24. The control system 24 determines the position of the accelerator pedal 26 and determines the amount of torque that needs to be produced by the motor 12 based on the accelerator pedal position. Accelerator pedal position sensing systems that are configured to send signals to the control system 24 that are indicative of the position of the accelerator pedal of a vehicle are known in the art, and any suitable system may be used.

[0029] Additionally, the control system 24 determines the position of the brake pedal 28. Brake pedal position sensing systems are also known in the art and any suitable system may be used. When the control system 24 determines that the brake pedal 28 has been depressed, the control system 24 may employ regenerative braking and may optionally also include some amount of mechanical braking. During regenerative braking, the control system 24 may operate the motor 12 to act as a generator, thereby braking the vehicle 10, and recovering brake energy with the motor 12 which may be sent to the battery pack 18 for storage.

[0030] The vehicle cabin 13 may be provided with a selector switch 30 that is used by the vehicle driver to select how aggressively the control system 24 is to apply regenerative braking when the brake pedal 28 is depressed and how aggressively to accelerate the vehicle 10 when the accelerator 26 is depressed. The selector switch 30 may be a physical switch, a series of buttons, or a virtual switch on a graphical user interface, such as a touch-screen mounted in the vehicle cabin 13. In the example shown, the switch 30 is a physical switch that is separate from a touch screen which is shown at 32. The switch 30 and the touch screen 32 may be part of an HMI (Human-Machine Interface) 34 for the vehicle 10.

[0031] The electric vehicle 10 further includes a range extender system 36 that is used to extend the range of the vehicle 10. The range extender system 36 may include a chemical-energy-based power unit, such as, for example, an internal combustion engine 38 (e.g. a spark ignition engine or a diesel engine) for generating mechanical energy from a fuel (e.g. gasoline or diesel) that is stored in a fuel tank 39, in combination with a generator 40 for generating electrical energy from mechanical energy. In the example shown, the generator 40 is an AC generator, and as a result, an AC-DC converter 42 is provided to convert the alternating current from the generator 40 to a direct current that is sent to the battery pack 18 to increase the state of charge (SOC) of the battery pack 18. Alternatively, the range extender system 36 may comprise a fuel cell stack that directly generates electrical energy from a fuel such as hydrogen. [0032] The control system 24 is configured to determine the SOC of the battery pack 18 and operate the range extender system 36 to control the SOC of the battery pack 18. The control system 24 may control the SOC of the battery pack 18 using the range extender system 36 according to a first control model (also referred to as a control strategy) illustrated in a drive cycle shown at 48 in Figure 3, in which the control system 24 is configured to:

a) permit depletion of the battery pack 18 from a fully charged SOC shown 50 to a first SOC 52,

b) charge the battery pack 18 using the range extender system 36 from the first SOC 52 to a second SOC 54 that is higher than the first SOC 52 but that is lower than the fully charged SOC 50, and

c) permit depletion of the battery pack 18 from the second SOC

54.

[0033] In step b), once the battery pack 18 reaches the second SOC 54 the control system 24 may shut off the range extender system 36 since the range extender system 36 is no longer needed for charging the battery pack 18. Optionally, in the first strategy the control system 24 is configured to deplete the battery pack 18 down to the first SOC in step c) and to carry out steps b) and c) a plurality of times, each time starting up the range extender system 36 to charge the battery pack 18. The phases of the drive cycle 48 where the battery pack 18 is being charged are referred to as charging phases and are shown at 53. The phases of the drive cycle 48 where the battery pack 18 is being depleted are shown at 51. The curve representing the SOC of the battery pack 18 is shown at 55. The graph in Figure 3 shows the SOC 55 (Y-axis in the graph) of the battery pack 0 over time (X-axis in the graph).

[0034] It will be noted that the control system 24 may initiate operation of the range extender system 36 at some point before the range extender system 36 is used to charge the battery pack 18, so that the range extender system 36 has time to warm up and reach a selected operating efficiency. The control system 24 may select the point in time at which to start operation of the range extender system 36 based on a current SOC of the battery pack 18, as compared to the first SOC 52, and based on an estimate of the amount of time remaining until the battery pack 18 reaches the first SOC 52. The points at which the range extender system 36 is started up are shown at 56. It will be noted that the first SOC 52 is a low SOC, but is above the minimum SOC of the battery pack 18 which is shown at 58. The minimum SOC 18 is a SOC below which the battery pack 18, depending on its chemistry, may be at risk of causing damage to some of the cells such that the battery pack 18 will not be able to reach a fully charged SOC afterwards. There is a risk of this problem occurring even if the battery pack 18 reaches the minimum SOC too often. To protect the battery pack 18, the first SOC 52 is at a level that is higher than the minimum SOC 58.

[0035] The average SOC of the battery pack 18 while the SOC fluctuates between the first and second levels 52 and 54 is shown by line 60. As can be seen the average SOC of the battery pack 18 remains generally constant throughout that period of repeated fluctuation. It will further be noted that the points 56 at which the range extender system 36 is started up are not intended to necessarily coincide with the points where the instantaneous SOC shown by line 55 intersects with the line 60 representing the average SOC. The points 56 could be above or below the points of intersection with line 60, or they may in some instances coincide with the points of intersection.

[0036] The first strategy may be followed using different values for some parameters. For example, in a non-limiting example, a 'Normal' mode may be provided, (and may be selected using the selector switch 30) in which the control system 24 may be configured to permit the motor 12 to receive the amount of current that the motor 12 was designed for without overheating or incurring damage (referred to as its design output). This may correspond to a vehicle acceleration of about 8 seconds to go from 0 to 60 mph. Also, in the Normal mode, the control system 24 may control the electricity produced during regenerative braking and may limit the current so that the force from the regenerative braking is less than about 0. 5G and may gradually taper to 0 as the speed of the vehicle 10 falls below 7 mph. It will be noted that the vehicle 10 also includes mechanical (e.g. disk) brakes that also apply a braking force to brake the vehicle 10, so that the total braking force is any suitable amount selected by the control system 24. In the Normal mode, the control system 24 may permit the battery pack 18 to be depleted to the minimum SOC 58 in circumstances where it is needed for the vehicle 10 to reach the top of a grade or to complete an acceleration event.

[0037] Reference is made to Figure 4, which shows the drive cycle 48 using the first strategy but with an 'Eco' mode for the parameters (again, selectable via the selector switch 30). In the Eco mode the control system 24 is configured to apply a greater current to the motor 12 during regenerative braking than is done in the 'Normal' mode (resulting in a regenerative braking force of up to, for example, 0.4G and tapering off to 0 for low vehicle speeds). The greater regenerative braking force increases the amount of energy is recouped by the battery pack 18 during braking or coasting of the vehicle 18. Additionally, in the Eco mode, the maximum acceleration that is permitted by the motor 12 may be lower than in the Normal mode. For example, in the Eco mode, the motor 12 may be limited to about 67% percent of its design output. In an example application this may result in an acceleration from 0 to 60 mph in about 12 seconds. This slows down the depletion of the battery pack 18 during the depletion phases 51 as compared to the rate of depletion that occurs during the depletion phases 51 in the Normal mode, and also speeds up the charging of the battery pack 18 during the charging phases 53 as compared to the rates that occur in the Normal mode.

[0038] . In the Eco mode, as with the Normal mode, the control system 24 may permit the battery pack 18 to be depleted to the minimum SOC 58 in circumstances where it is needed for the vehicle 10 to reach the top of a grade or to complete an acceleration event.

[0039] In both the Eco and Normal modes, the amount of fluctuation of the SOC of the battery pack 18 that is permitted between the first and second SOCs 52 and 54 may be a selected value, such as, for example, about 20% of the total amount of energy the battery pack 18 can hold. The average SOC 60 may be a value of about 20% of the fully charged SOC available for the battery pack 18. Thus the SOC may fluctuate between about a 10% SOC (first SOC points 52 in Figure 3) and a 30% SOC (second SOC points 54 in Figure 3).

[0040] Also, in both the Eco and Normal modes, the battery pack 18 may be permitted to go to the minimum SOC 58 (which may be, for example, about a 5% SOC) when needed for grades or acceleration events.

[0041] Figure 5 shows the drive cycle 48 using the first strategy with an 'Maximum Temporary Power' (MTP) mode, selected with the selector switch 30. In the MTP mode, the control system 24 sets the first SOC 52 to be the minimum SOC 58, and sets the second SOC 54 to be relatively higher than the second SOC 54 when in the Normal or Eco modes. The average SOC 56 of the battery pack 18 may be higher than in the Normal or Eco modes (e.g. about 50% SOC). Also, the range of SOC over which battery pack 18 is permitted to fluctuate between the first and second SOCs 52 and 54 may be larger than in the Normal and Eco modes. In the embodiment shown the SOC may fluctuate by about 45%. [0042] In the MTP mode, the control system 24 may permit operation of the motor 12 at an output level that is greater than the design output (e.g. 133% of design output) for short periods of time (e.g. to permit bursts of acceleration when desired). As a result, the motor 12 may overheat temporarily, however, power may be cut to the motor 12 in the event that the motor temperature increases to a critical threshold temperature, or after a selected period of time passes (e.g. 10 seconds). In an example embodiment, in the MTP mode the vehicle 10 may be capable of an acceleration from 0 to 60 mph in about 6 seconds.

[0043] In the MTP mode the control system 24 may also provide a high regenerative braking force (e.g. up to 0.4G), as this may increase the overall braking force that can be applied, at least as compared to the Normal mode, thereby providing improved braking performance.

[0044] In any of the Normal, Eco, or MTP modes, the control system 24 may permit the range extender system 36 to be used to send at least some electrical power from the generator 40 directly to the inverter 22 (or to the controller for the inverter 22) to drive the motor 12, instead of sending all of the electrical power from the generator 40 to the battery pack 18 (via the AC-DC converter 42).

[0045] As can be seen in Figures 3, 4 and 5, the first control strategy utilizes the range extender system 36 to maintain an average SOC 60 of the battery pack 18 that may be well below the fully charged SOC 50 and that may be near the minimum SOC 58. Such a control strategy may be beneficial when the vehicle 10 is being used on a short trip and it is desired to avoid use of the range extender system 36 as long as possible, to avoid consuming fuel as long as possible. Reference is made to Figure 6, which shows a second strategy that may be used by the control system 24 to control the state of charge of the battery pack 18. Using the second control strategy, the control system 24 may be configured to maintain the battery pack 18 at an SOC that is relatively close to the fully charged SOC. Such a control strategy is beneficial if the vehicle 10 is being driven to a location where it is desired or required for the vehicle 10 to be used without emitting any pollutants. A drive cycle 148 is shown in Figure 6. As can be seen in Figure 6, using the second control strategy, the control system 24 is configured to:

d) permit depletion of the battery pack 18 from a fully charged state of charge to a third state of charge shown at 152,

e) charge the battery pack using the range extender system 36 from the third state of charge 152 to a fourth state of charge 154 in which the battery pack 18 is substantially fully charged, and

f) permit depletion of the battery pack 18 from the fourth state of charge 154. The instantaneous SOC of the battery pack 18 is represented by curve 155. As shown in Figure 6, the average SOC (shown at 160) of the battery pack 18 may be about 85% to about 90% and the range of SOCs between the third and fourth SOCs 152 and 154 may be about 20% (similar to the range using the first control strategy). However, using the first control strategy the vehicle 10 may arrive at a destination with its battery pack 18 substantially depleted, or well below the fully charged SOC, whereas using the second control strategy the vehicle 10 arrives at a destination with the battery pack 18 near the fully charged SOC (shown at 150).

[0046] Figure 6 may represent operation of the vehicle 10 in a 'Normal' mode using the second control strategy. The Normal mode may be similar to the Normal mode in the first control strategy in terms of the output of the motor 12, the amount of regenerative braking force that is provided and the permission by the control system 24 to dip below the third SOC 152 to a minimum SOC shown at 158 during events where it is needed (e.g. during an acceleration event or when climbing a grade). As can be seen, the slopes of the depletion phases shown at 151 and the slopes of the charging phases 153 may be similar to the slopes of the depletion and charging phases 51 and 53 shown in Figure 3, which indicates that the charging and depletion rates may be similar in the Normal mode for the first and second strategies. Figure 7 shows an Eco mode for the second control strategy. In the Eco mode, the values for the regenerative braking force, the motor output and other parameters may be similar to the values used in the Eco mode in the first control strategy shown in Figure 4, except that the average SOC 160 for the battery pack 18 is kept near the fully charged SOC 150. With reference to Figure 8, in the MTP mode for the second strategy, the values for the regenerative braking force and the motor output may be similar to the values used in the MTP mode in the first control strategy shown in Figure 5. It will be noted however, that the value of the minimum SOC 158 used in the MTP mode in Figure 8 may be lower than the minimum SOC 158 used in the Normal and Eco modes shown in Figures 6 and 7.

[0047] Reference is made to Figure 9 which shows another control strategy that could be used by the control system 24. Using the control strategy in Figure 9, the control system 24 is configured to:

g) permit depletion of the battery pack 18 from a fully charged state of charge 250 to a third state of charge 252,

h) charge the battery pack 18 using the range extender system 36 from the third state of charge 252 to a fourth state of charge 254,

i) permit depletion of the battery pack 18 from the fourth state of charge 254 to a fifth state of charge 262 that is higher than the third state of charge 252, and

j) charge the battery pack 18 using the range extender system 36 from the fifth state of charge 262 to a sixth state of charge 264.

[0048] In an alternative embodiment the fifth SOC 262 may not necessarily be higher than the third SOC 252, and instead the sixth state of charge is higher than the fourth state of charge. In another embodiment the fifth

SOC 262 is higher than the third SOC 252, and the sixth state of charge is higher than the fourth state of charge. [0049] Using the strategy shown in Figure 9, the control system 24 permits depletion of the SOC (shown at 255) of the battery pack 18 to a selected SOC (i.e. the third SOC 252), and then proceeds through cycles where the battery pack 18 is depleted (shown at 251 ) and charged (shown at 253) in such a way that the average SOC shown at 260 progressively increases such that, when the vehicle 10 arrives at a selected destination, the battery pack 18 is at a selected final SOC 368 (e.g. substantially fully charged). In the embodiment shown, the user (e.g. the vehicle driver) may input information to the control system 24 via the touch screen 32 relating to the destination that the vehicle 10 is being driven to, the route being taken to the destination, the SOC that is desired for the vehicle 10 upon reaching the destination, and any other suitable information. In such an embodiment, the vehicle 10 may be equipped with an on-board navigation system (shown at 99 in Figure 2) that accesses map data stored on-board (e.g. on a DVD) or that accesses map data stored externally (e.g. via a wireless connection to the internet). In Figure 9, the vehicle 10 reaches the destination at a point in time 270 at the final SOC, shown at 268, which is a full SOC. The control system 24, in order to reach the destination with the correct final SOC 268 may use the map data and the route selected by the user to adjust the points at which to begin and stop charging the battery pack 18. After reaching the destination, the SOC of the vehicle 10 may be controlled according to a different strategy if desired. During the depletion and charging phases 251 and 253, the control system 24 may determine a minimum state of charge 258 that the battery pack 18 can be depleted to. In the embodiment shown, it can be seen that the minimum SOC 258 can change (e.g. increase) as the vehicle 10 proceeds through the drive cycle 248.

[0050] Reference is made to Figure 10 which shows another strategy that may be used to control the SOC of the battery pack 18. The drive cycle is shown at 348. The instantaneous SOC of the battery pack 18 is represented by line 355. According to the control strategy illustrated, the control system 24 is configured to

k) permit depletion of the battery pack 18 from a fully charged state of charge 350 to a third state of charge 352,

I) charge the battery pack 18 using the range extender system 36 from the third state of charge 352 to a fourth state of charge 354,

m) permit depletion of the battery pack 18 from the fourth state of charge 354 to a fifth state of charge 362, and

n) charge the battery pack 18 using the range extender system 36 from the fifth state of charge 362 to a sixth state of charge 364 that is lower than the fourth state of charge 362. In the embodiment shown, the third and fifth SOCs 352 and 362 are the same and are both slightly above the minimum SOC, shown at 358. In the embodiment shown in Figure 10, the minimum SOC 358 may be the threshold SOC below which the battery pack 18 is at risk of incurring damage to one or more cells that would prevent the battery pack 18 from subsequently reaching a fully charged state of charge. The minimum SOC 358, in similar fashion to the minimum SOC 58 in Figure 3, represents an SOC that, if reached too often, has some risk of causing damage to one or more cells potentially preventing the battery pack 18 from subsequently reaching a full state of charge 350, but that is likely to not cause such a problem if reached only occasionally. The third SOC 352 is an SOC that is close to the minimum SOC 358 but that is substantially safe from this aforementioned issue.

[0051] In the control strategy illustrated in Figure 10, the vehicle 10 arrives at a destination substantially depleted of energy (i.e. the final SOC, shown at 368, is substantially at a safe value that is close to the minimum SOC 358, but that does not cause a risk of damage to the cells of the battery pack 18. This means that any charge that was generated using fuel and the range extender 36 was ultimately used during the drive cycle 348, which means that the vehicle 10 did not burn any fuel unnecessarily. Thus, this strategy is useful for maintaining low total emissions during travel to a destination. To carry out this control strategy the control system 24 may be configured to receive input from a user (e.g. via the touch screen 32) regarding the destination and the route to be taken to reach the destination. In this embodiment the vehicle 10 may be equipped with a navigation system 99 (Figure 2). With this information the control system 24 can, using the map data, determine what the fourth and sixth SOCs 354 and 364 should be (as well as each subsequent SOC that triggers the control system 24 to charge or stop charging the battery pack), ultimately reaching the final SOC 368 at a point at the point in time shown at 370 when the vehicle 10 arrives at the destination.

[0052] It will be noted that the average SOC shown at 360 varies progressively downward as the vehicle 10 travels towards the destination.

[0053] Reference is made to Figure 1 1 , which shows a drive cycle 448 in which the SOC of the battery pack 18 is controlled according to another control strategy, in which a user of the vehicle 10 selects the third and fourth SOCs (shown at 452 and 454 respectively) that the battery pack 18 is to fluctuate between. For example, the control system 24 can receive input from a user via the touch screen 32 regarding the third and fourth SOCs 452 and 454. The control system 24 permits depletion of the SOC 455 from the full SOC shown at 450 to the third SOC 452 at which point the control system 24 uses the range extender system to charge the battery pack 18 to the fourth SOC 454 at which point the control system 24 stops charging the battery pack 18 and permits depletion of the battery pack 18 back to the third SOC 452. It will be noted that by selecting the third and fourth SOCs 452 and 454, the user is implicitly selecting the average SOC 460 that the battery pack 18 fluctuates about during the drive cycle 448. Instead of implicitly selecting the average SOC 460 by selecting the third and fourth SOCs 452 and 454, the control system 24 may permit the user to select the average SOC 460 and may select third and fourth SOCs 452 and 454 based on the average SOC 460 selected by the user. [0054] When operating according to this strategy the control system 24 may be operable in a plurality of modes (e.g. the Normal, Eco and MTP modes). Figure 11 shows the Normal mode, which may be similar in terms of the values of the parameters for the regenerative braking force, the maximum amount of power output from the motor 12, and other factors, to the Normal mode illustrated in Figure 3. Figures 12 and 13 depict Eco and MTP modes respectively, and may be similar in terms of the impact on maximum motor output and regenerative braking force to the Eco and MTP modes described in relation to Figures 4 and 5, with similar effect on the slopes of the depletion phases shown at 451 and the charging phases shown at 453. As can be seen the third and fourth SOCs 452 and 454 may be changed from their values in the Normal and Eco modes when the MTP mode is selected.

[0055] Figure 14 illustrates a control strategy in which the user inputs a destination and a route to the destination using an input device such as the touch screen 32. The user also inputs a desired final SOC shown at 568 for the battery pack 18 upon arrival at the destination. As can be seen with the drive cycle shown at 548, the control system 24 controls the depletion and charging of the battery pack 18 so that the battery pack 18 has the desired final SOC 568 at the point in time 570 that the vehicle 10 arrives at the destination. The control system 24 may use data from an on-board navigation system 99 (Figure 2) to detect when the vehicle 10 is approaching an upward grade or a downward grade, and may start up the range extender system 36 as needed to ensure that the battery pack 18 has sufficient power for the motor 12 to propel the vehicle 10 up any upward grades. Aside from showing the instantaneous SOC at 555 in Figure 14, the instantaneous elevation along the route is shown at 565. It can be seen that, in general, as the vehicle 10 climbed (i.e. gained in elevation as shown at 561 ) the SOC 555 of the battery pack 10 dropped (shown at 551) and as the vehicle 10 descended (i.e. dropped in elevation as shown at 563) the SOC 555 increased (553). It can also be seen that in general, points corresponding to peaks in elevation (shown at 574) may generally correspond to SOCs where the control system starts charging the battery pack 18 (shown at 552), and points corresponding to local low points in elevation (shown at 572) may generally correspond to points where the control system 24 stops charging the battery pack 18 (shown at 554). This is due at least in part to the use of regenerative braking on the downward grades, and the need to consume energy on the upward grades. The full SOC is shown at 550.

[0056] If the control system 24 determines that the vehicle is climbing a grade but that a descent is approaching shortly, the control system 24 may determine that the battery pack 18 has enough charge to complete the ascent of the grade and may stop the charging process before the vehicle 10 reaches the top of the grade. Conversely, during a descent, the control system may start charging the battery pack 18 before the completion of the descent in order to stockpile charge in the event that a large upward grade is approaching. [0057] Figures 3, 6, 9, 10, 1 1 and 14 all illustrate different control strategies for controlling the SOC of the vehicle 10. If the vehicle 10 is provided with a plurality of these control strategies, the user is able to tailor the fuel consumption of the vehicle 10 so as to arrive at a destination having consumed a selected amount of fuel and having a selected SOC. The vehicle 10 is thus better able to handle different types of situations while providing low emissions in each situation. In an example, the control system 24 of the vehicle 10 may be programmed with the control strategy shown in Figure 3, and one or more of the control strategies shown in Figures 6, 9, 10, 1 1 and 14. The user of the vehicle 10 may select which strategy to use via the touch screen 32. The control system 24 may be programmed with all of the control strategies described herein.

[0058] In addition to being programmed with a plurality of control strategies, the control system 24 is also capable of varying selected parameters via the selector switch 30, permitting the user to choose a mode of operation (e.g. Normal, Eco, and MTP). This provides the user with additional control over the operating characteristics of the vehicle 10.

[0059] It will be noted that in some embodiments, the control system 24 may be programmed with only a single control strategy, such as the strategy illustrated in Figure 1 1 , in which the user is able to select whatever final SOC is desired, or the strategy illustrated in Figure 10, in which the vehicle 10 reaches a destination substantially depleted of electrical charge (i.e. depleted down to substantially the lowest safe level). In situations where the vehicle 10 is provided with only one control strategy, and it is one of the strategies shown in Figures 6-14, references to a third SOC, a fourth SOC, a fifth SOC and a sixth SOC will be understood to be instead a first SOC, a second SOC, a third SOC and a fourth SOC respectively. For example, if the vehicle 10 were not programmed with the control strategy shown in Figure 3, and was programmed only with the control strategy shown in Figure 9, the third, fourth, fifth and sixth SOCs 252, 254, 262 and 264 would be referred to instead as first, second, third and fourth SOCs 252, 254, 262 and 264.

[0060] It will be understood that the touch screen 32 and the selector switch 30 are merely examples of input devices and that any other suitable input device or input devices could be used.

[0061] While the above description constitutes a plurality of embodiments, it will be appreciated that the examples shown and described herein are susceptible to further modification and change without departing from the fair meaning of the accompanying claims.