AN ENERGY HARVESTING POWER-ASSIST SYSTEM AND METHOD FOR
LIGHT VEHICLES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit and priority of U.S. Provisional patent application Serial No. 62/252,568 filed November 8, 2015 entitled HUMAN-ELECTRIC POWERED (HEP) HYBRID TRANSAXLE DRIVE APPARATUS AND METHOD FOR LIGHT VEHICLES, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to power-assisted light vehicles in which human power is supplemented by electric power, and in particular to an energy-harvesting system which requires no external electrical charging and thus has unlimited range.
BACKGROUND OF THE INVENTION
[0003] Power-assisted light vehicles such as bicycles, pedicabs and wheelchairs are well known in existing practice. Many such vehicles employ electrical power-assist with an electrical energy storage device such as a battery. However, all such vehicles in existing practice have limited range of operation due to the finite storage capacity of the energy storage device. Once the stored energy has been exhausted, power-assist is no longer available until there is access to an external energy source which can re-charge the storage device. Such limited range is a severe disadvantage which detracts from the usefulness of these devices in existing practice.
There therefore exists a need for a power-assist system which does not require any external charging and therefore has effectively unlimited range.
SUMMARY OF THE INVENTION
[0004] Accordingly, it is a general objective of the present disclosure to have an apparatus and method for providing power-assist with unlimited range of operation.
[0005] It is further an objective of the present disclosure to have an apparatus and method for providing power-assist to the user when there is a power demand that exceeds a preset value which is selected by the user based on a desired level of effort.
[0006] These objectives are achieved with a closed energy system wherein energy is continuously harvested and stored in a high capacity energy storage device. This energy is available for later use when there is a demand for power-assist. The system does not require any other external energy source and hence never needs to be charged under the described usage cases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Fig. 1A is a schematic representation of an energy harvesting power-assist system according to the present disclosure.
[0008] Fig. IB is a conceptual representation of the theory of operation of an embodiment of an energy harvesting power-assist system according to the present disclosure.
[0009] Fig. 1C is a schematic showing details of an embodiment of an energy harvesting power-assist system according to the present disclosure.
[0010] Fig. 2 is a schematic showing the flow of energy in cold start mode according to the present disclosure.
[0011] Fig. 3 is a schematic showing the flow of energy in soft coasting mode according to the present disclosure.
[0012] Fig. 4 is a schematic showing the flow of energy in hard coasting mode according to the present disclosure.
[0013] Fig. 5 is a schematic showing the flow of energy in soft cruising mode according to the present disclosure.
[0014] Fig. 6 is a schematic showing the flow of energy in hard cruising mode according to the present disclosure.
[0015] Fig. 7 is a schematic showing the flow of energy in kinetic energy harvesting mode according to the present disclosure.
[0016] Fig. 8 is a flow chart of an energy flow control method according to the present disclosure.
[0017] Fig. 9 is a schematic of a drive assembly according to the present disclosure.
[0018] Fig. 10 shows an energy harvesting power-assist system according to the present disclosure mounted on a bicycle.
[0019] Fig. 11A is a right side exploded isometric view of a drive assembly according to the present disclosure.
[0020] Fig. 1 IB is a left side exploded isometric view of a drive assembly according to the present disclosure.
[0021] Fig. 12 is a side view of a drive assembly according to the present disclosure.
[0022] Fig. 13 is a horizontal cross-section of a drive assembly according to the present disclosure.
[0023] Fig. 14 is a cross-section through a planetary gear according to the present disclosure.
[0024] Fig. 15 is a cross-section through a front sprocket ratchet according to the present disclosure.
[0025] Fig. 16 is a cross-section through a motor/generator and high capacity storage elements according to the present disclosure.
DET AILED DESCRIPTION OF PREFERRED EMBODIMENT
[0026] Note that in the description below, and in the figures, energy flows are labeled using the convention E-XXX, where XXX is the reference numeral of the energy flow being considered. Also in the description and figures, information signal lines are labeled using the convention S-YYY, where YYY is reference numeral of the signal line being considered.
Overview of Apparatus and Method
[0027] Fig. 1A is a schematic representation of an energy harvesting power-assist system for a light vehicle according to the present disclosure. The user applies user energy E-102 to an energy splitter unit 102 which splits a small amount E-101 of the user energy for storage in a high capacity storage unit 112. The magnitude of split energy E-101 depends on the operating mode of the light vehicle (see section on "Power Management" below), but in general split energy E-101 may comprise from 1% to 20% of user energy E-102. Split energy E-101 is converted to electrical energy by a motor/generator assembly 108 operating in generator mode, via a control unit 110 which controls the flow of energy between high capacity storage unit 112 and motor/generator assembly 108. A larger remaining proportion E-103 of user energy E-102 is directed to an energy combiner assembly 105 which combines energy E-103 with energy E-109 from motor/generator assembly 108 operating in motor mode. The energy output E-105 of energy combiner assembly 105 is applied to a driven wheel 106 of the light vehicle.
[0028] In kinetic energy harvesting mode, kinetic energy E-106 may be recovered from wheel 106 and transmitted as energy E-107 to motor/generator assembly 108 operating in generator mode, which converts the kinetic energy to electrical energy for storage in high capacity storage unit 112.
[0029] Control unit 110 receives a user-defined effort level input signal S-110 which defines the desired maximum level of user energy E-102. If the required effort level is greater than effort level input S-110, control unit 110 will cause motor/generator assembly 108 to draw energy from high capacity storage unit 112, and to deliver energy E-109 to
provide power-assist to the user. If the required effort level is less than effort level input S-110, control unit 110 will cause motor/generator assembly 108 to either receive recovered kinetic energy E-107 or to harvest split energy E-101 for conversion to electrical energy and storage in high capacity storage unit 112. Note that, while the user is applying user energy E-102, split energy E-101 is continuously available for conversion and storage in high capacity storage unit 112.
[0030] Fig. IB is a conceptual representation of the theory of operation of an embodiment of the energy harvesting power-assist system. In the illustrated embodiment, motor/generator assembly 108 comprises a first motor/generator 7 (MG1) and a second motor generator 8 (MG2). Energy combiner assembly 105 comprises an energy combiner unit 104, an energy selector unit 104a and an energy selector unit 104b.
[0031] In the embodiment of Fig. IB, energy splitter unit 102 splits a small amount E-101a and E-101b of user energy E-102 for storage. Energy selector units 104a and 104b are configured to transmit either split energy components E-101a and E-101b respectively, or kinetic energy components E-106a and E-106b respectively. The outputs of energy selector units 104a and 104b are selected energies E-107a and E-107b respectively and the selected energies are transmitted to MG2 and MG1 respectively. Energy selector units 104a and 104b are configured to operate independently of one another, thereby providing four possible outputs as shown in Table 1.
Table 1
[0032] Selected energies E-107b and E-107a are converted to electrical energy by MG1 and MG2 respectively, operating in generator mode. The electrical energy is stored in high capacity energy storage device 112.
[0033] The stored energy is available for later use and may be converted back to mechanical energy by MG1 and/or MG2 operating in motor mode. One or both motors may engage depending on the level of power-assist demanded. Energy combiner unit 104 combines all energy sources, namely E-103 from the user and E-109b and E-109a from MG1 and MG2 respectively, operating in motor mode. Energy output E-105 from energy combiner unit 104 is transferred to driven wheel 106 of the light vehicle.
[0034] In an embodiment, energy splitter unit 102, energy combiner unit 104, and energy selector units 104a and 104b may all be implemented by means of a single electromechanical assembly as described below.
[0035] Fig. 1C shows a schematic representation of the apparatus of an embodiment of the light vehicle power-assist system. The system consists of a drive assembly 100, electronic control unit 110 and high capacity energy storage device 112. Drive assembly 100 comprises pedals 132, a crank axle 1, energy splitter unit 102, motor/generators MG1 and MG2, energy combiner unit 104, and energy selector units 140a and 104b (not shown). Drive assembly 100 also includes a sprocket and chain (see Fig. 10), or other mechanical connection system, to transfer power to wheel 106. In an embodiment, MG1 and MG2 are coreless dual Halbach array permanent magnet axial AC motor/generators.
[0036] High capacity energy storage device 112 comprises a plurality of high capacity storage elements 111, comprising ultra-capacitors 111a, hereinafter referred to as UCAP, and high capacity battery cells 111b, hereinafter referred to as BAT. UCAP 111a functions as short term energy cache storage, handling peak demands of less than about 10 minutes' duration with many rapid charge/discharge cycles, while BAT 111b provides energy for longer term demands of greater than about 10 minutes' duration. In an embodiment, high capacity battery cells 111b may comprise Li ion battery cells. In a further embodiment, ultra-capacitors 111a may comprise thin supercapacitors.
[0037] Note that control unit 110 is configured to control high capacity storage elements 112 so that BAT 111b always retains a minimum energy level, but UCAP 111a may be fully depleted.
[0038] Electronic control unit 110 comprises a controller 122, DC-AC inverters 128a and 128b, an AC-DC rectifier and battery management system (BMS) 138, an auxiliary inputs and connectivity unit 142, and an auxiliary power DC-DC converter 140.
[0039] The DC energy stored in energy storage device 112 is converted to AC current by DC-to-AC inverters 128a and 128b. The AC output of DC-to-AC inverters 128a and 128b feeds motor/generators MG2 and MGl respectively (motor mode). MG2 and MGl include a plurality of Hall effect sensors, 130a and 130b respectively, which feed back rotor phase information from MG2 and MGl to DC-to-AC inverters 128a and 128b respectively. High capacity energy storage device 112 is charged by motor/generators MGl and MG2 (generator mode). MGl and MG2 are connected to AC-DC rectifier and BMS 138 which provides the charge to high capacity energy storage device 112. Controller 122 controls DC-AC inverters 128a and 128b, and AC-DC rectifier and BMS 138 in a closed loop, with closed loop control feedback being provided by a torque and cadence (RPM) sensor 11 mounted in crank axle 1. The feedback loop reference is effort level input S-110 selected by the user.
[0040] Auxiliary power DC-DC converter 140 converts part of the stored energy in high capacity energy storage device 112 to a suitable voltage to power headlights and other accessories (e.g. a mobile phone). Auxiliary inputs and connectivity unit 142 has two main functions:
(a) There is provision for inputs from various sensors, such as a Global Positioning System (GPS), an accelerometer (ACCEL), and an inclinometer (INCLINO), all of which may be used to improve the utility of the apparatus and method described herein; and
(b) There is connectivity to a BlueTooth (BT) module which is used for communication between the apparatus and a mobile phone. In an embodiment, the BT connection may be the method by which the user enters effort level input S-110 by means of a mobile phone.
[0041] Energy splitter 102 is capable of splitting a small energy amount from crank axle 1 to motor/generators MGl and MG2. This energy is stored in high capacity energy storage
device 112 for later use. Storage of user split energy E-101 occurs as long as the user is pedaling. If the user is not pedaling but the light vehicle is still in motion, storage of kinetic energy E-106 occurs. In either case, controller 122 determines the amount of energy to store based on storage depletion levels in high capacity energy storage device 112. Controller 122 also determines if there is a need for power-assist, and if so, stored energy from high capacity energy storage device 112 is converted to mechanical energy by motors MGl and MG2, and is transferred to light vehicle wheel 106 through a sprocket system which is described below. A mechanical embodiment of drive assembly 100 is described in further detail in the Description of Mechanical Embodiment section below.
Description of Mechanical Embodiment
[0042] This section provides a detailed description of mechanical embodiments of the power-assist system. The description is made with reference to Figs. 9 ~ 16.
[0043] Fig. 9 shows a schematic of drive assembly 100, and Fig. 10 shows an example of the power-assist system, including drive assembly 100, mounted on a bicycle. Referring to Fig. 9, a front sprocket ratchet 2 comprises an inside front sprocket ratchet 2a and an outside front sprocket ratchet 2b. Crank axle 1 is the axle of drive assembly 100 and is connected to inside front sprocket ratchet 2a. A front sprocket 3 is connected to outside front sprocket ratchet 2b. Front sprocket ratchet 2 forms a one-way clutch that transfers torque from pedals 132 to front sprocket 3 in the clockwise (CW) direction only, and decouples front sprocket 3 from crank axle 1 in the counter clockwise (CCW) direction. When crank axle 1 rotates in CW direction faster than front sprocket 3, the user's generated torque is transferred from the crank axle 1 to front sprocket 3, otherwise torque is not transferred.
[0044] Front sprocket 3 is the power output element where the torques of the user and motors MG1/MG2 are combined, and as such it is a mechanical embodiment of energy combiner assembly 105. As shown in Fig. 10, power from front sprocket 3 may be transferred to a rear sprocket 12 by a chain or belt 13. Rear sprocket 12 is fixed to the axle of light vehicle wheel 106 such that rotation of wheel 106 may drive rotation of front sprocket 3 through chain or belt 13 when the speed of rotation of rear sprocket 12 is greater
than the speed of rotation of crank axle \. This driven rotation of front sprocket 3 forms the basis of kinetic energy recovery as illustrated by harvested kinetic energy E-106a and E-106b in Fig. 7.
[0045] Fig. 14 shows a cross section of a planetary (epicyclic) gear 4, which comprises a planetary ring 4a, planets 4b, a planetary sun 4c, and a planets carrier 4d (shown in Fig. 1 IB). Planetary gear 4 is an exemplary mechanical implementation of energy splitter unit 102, and is mounted coaxially on crank axle 1 on bearings 5 (see Fig. 13). Outside front sprocket ratchet 2b is also connected to planets carrier 4d which is the carrier for planets 4b.
[0046] A planetary ring ratchet 6 comprises an inside planetary ring ratchet 6a and an outside planetary ring ratchet 6b (see Fig. 13). Planetary ring 4a is connected to inside planetary ring ratchet 6a, while outside planetary ring ratchet 6b is fixed to a stationary housing 10. Note that stationary housing 10 is stationary relative to the frame of the light vehicle. Inside and outside planetary ring ratchets 6a and 6b together form ring ratchet 6 which is a one-way clutch allowing rotation of the ring gear in CW direction only and locking the ring gear to stationary housing 10 in the CCW direction.
[0047] Motor/generators 7 (MG1) and 8 (MG2), having rotors 7a and 8a respectively and stators 7b and 8b respectively (see Fig. 13), are coaxially mounted on planetary sun 4c (see Fig. 11B). MG1 is mounted on a bearing 9, while MG2 is directly coupled to planetary sun 4c. MG2 is a mid/high torque drive unit, while MG1 is a low/mid torque drive unit. In an embodiment, both units may consist of dual Halbach array permanent magnet axial motor/generators. As shown in Fig. 13, both stators 7b and 8b are fixed to stationary housing 10.
[0048] MG1 rotor 7a is connected to planetary ring 4a and can only rotate in CW direction due to planetary ring ratchet 6. The main function of ring ratchet 6 is to enable MG2 to transfer torque to front sprocket 3 during cold start, corresponding to energy E-109a as illustrated in Fig. 2.
[0049] Stationary housing 10 is the housing for drive assembly 100, and it is fixed to the light vehicle frame. Housing 10 may be split in sections to allow assembly. As shown in Figs. 11A and 11B, housing 10 also encloses high capacity storage elements 111 and electronic control unit 110. Housing 10 may be fixed to the light vehicle frame by means of a housing bottom bracket mount 10a (see Figs. 11A and 13). Housing bottom bracket mount 10a is a part of housing 10 that fits inside a commercially available bicycle bottom bracket 16. As shown in Fig. 11 A, housing bottom bracket mount 10a is threaded at one end such that the threaded portion protrudes from bottom bracket 16 and allows installation of a locknut 14. A housing lug 15 locks the housing rotationally against the bicycle frame.
[0050] As shown in Figs. 11 and 13, torque and cadence sensor 11 is directly coupled to crank axle 1. In an embodiment, sensor 11 may also incorporate the bearings for crank axle 1.
[0051] In an alternative embodiment of drive assembly 100, MG1 and MG2 are not coaxially mounted on the axis of planetary gear 4. In this embodiment, MG1 and MG2 may be mounted with their axis at a certain distance from the axis of planetary gear 4. Both motor/generators accomplish the same functions described in the first embodiment by means of a mechanical transmission that bridges the distance between the axis of MG1 and MG2 and the axis of planetary gear 4. Such a mechanical transmission may be accomplished, for example, with a gear set, or sprockets and timing belts.
[0052] MG1 and MG2 may alternatively be DC brushless permanent magnet motor/generators instead of the Halbach array type.
[0053] It should be noted that Fig. 10 illustrates a bicycle only as an exemplary embodiment. The invention may be installed on a pedicab, a wheelchair or any other light vehicle, and all such embodiments are within the scope of the present disclosure.
[0054] It should also be noted that planetary gear 4 may be implemented as a single stage gear as shown, or could alternatively be implemented as a multi-stage planetary gear system with various gear ratios as required to achieve a desired performance or to match
the torque characteristics of a particular motor/generator. All such variations of implementation of the planetary gear system are within the scope of the present disclosure.
System Power Management
[0055] This section describes all usage cases of the energy harvesting power-assist system and energy flows for each case. The usage cases are illustrated in Figs. 2 ~ 7 in which energy delivered to light vehicle wheel 106 is shown with bold lines, and energy that is harvested and stored in high capacity energy storage device 112 is shown in bold broken lines. Also in Figs. 2 - 7 the active elements for each given usage case are shown with bold line borders.
Cold Start:
[0056] Power flows for cold start are shown in Fig. 2. The user starts pedaling to get the light vehicle in motion, MG2 assists by providing power in CW direction so as to reduce the initial required starting torque from the user. Ring ratchet 6 prevents MG1 from rotating in the CCW direction. Pedals 132 and front sprocket 3 are engaged in CW direction by front sprocket ratchet 2. The power flows are as follows:
Pedal 132 wheel 106 (Energy E-103)
MG1 open circuit
UCAP/BAT MG2 wheel 106 (Energy E-109a) Soft Coasting
[0057] Power flows for soft coasting are shown in Fig. 3. Soft coasting is a low riding resistance case, typically when riding without headwind on a flat smooth surface. No pedal assist is required and the user pedals at a comfortable cadence (for example, 60-70 rpm) without exceeding effort level input S-110. Ring ratchet 6 prevents MG1 from rotating in the CCW direction. Pedals 132 and front sprocket 3 are engaged in CW direction by front sprocket ratchet 2. MG1 and MG2 rotate at approximately 200 rpm and 600 rpm respectively, and charge UCAP 111a and BAT 111b. The power flows are as follows:
Pedal 132 wheel 106 (Energy E-103)
Pedal 132 MG1 UCAP/BAT (Energy E-101b)
Pedal 132 MG2 UCAP/BAT (Energy E-101a)
Note that, depending on charge levels of UCAP 111a and BAT 111b, the harvested energy (E-101a + E-101b) may be between 5% and 20% of user energy E-102.
Hard Coasting
[0058] Power flows for hard coasting are shown in Fig. 4. Hard coasting is a low-mid riding resistance case, typically when riding with moderate headwind on a flat smooth surface. No pedal assist is required. The user pedals at a comfortable cadence (for example, 60-70 rpm) without exceeding effort level input S-110. Ring ratchet 6 prevents MGl from rotating in the CCW direction. Pedals 132 and front sprocket 3 are engaged in CW direction by front sprocket ratchet 2. MG2 rotates at 400 rpm and charges UCAP/BAT. The power flows are as follows:
Pedal 132 wheel 106 (Energy E-103)
MGl open circuit
Pedal 132 MG2 UCAP/BAT (Energy E-101a)
Note that, depending on charge levels of UCAP 111a and BAT 111b, the harvested energy (E-101a) may be between 1% and 10% of user energy E-102.
Soft Cruising
[0059] Power flows for soft cruising are shown in Fig. 5. Soft cruising is a medium riding resistance case, typically when riding with a light headwind and/or on a gentle slope. Pedal assist is required and is given by MG2. The rider pedals at a comfortable cadence (for example, 60-70 rpm) at effort level input S-110. Pedals 132 and front sprocket 3 are engaged in CW direction by front sprocket ratchet 2. Ring ratchet 6 prevents MGl from rotating in the CCW direction. MG2 rotates in CW or CCW direction depending on the relative speeds of planets carrier 4d and planetary ring 4a and assists pedaling as needed. MGl rotates in CW direction and charges UCAP/BAT. Control unit 110 charges UCAP 111a first, and when UCAP 111a is fully charged excess power is used to charge BAT 111b. MG2 draws the necessary power from UCAP 111a or BAT 111b. The power flows are as follows:
Pedal 132 wheel 106 (Energy E-103)
Pedal 132 MGl UCAP/BAT (Energy E-101b)
UCAP/BAT MG2 wheel 106 (Energy E-109a)
Note that, depending on charge levels of UCAP 111a and BAT 111b, the harvested energy (E-101b) may be between 1% and 10% of user energy E-102.
Hard Cruising
[0060] Power flows for hard cruising are shown in Fig. 6. Hard cruising is a high riding resistance case, typically when riding with strong headwind and/or on a steep slope (for example, slope > 6%). Pedal assist is required and is delivered by both MGl and MG2. The user pedals at a comfortable cadence (for example, 30-50 rpm) at effort level input S- 110. Ring ratchet 6 prevents MGl from rotating in the CCW direction. Pedals 132 and front sprocket 3 are engaged in CW direction by front sprocket ratchet 2. MGl rotates in CW direction and assists pedaling as needed. MG2 rotates in CW or CCW direction depending on the relative speeds of planets carrier 4d and planetary ring 4a, and is equivalent to a low gear assist. MGl and MG2 both draw the necessary power from UCAP 111a or BAT 111b. This hard cruising mode of operation is meant to be of relatively short duration, in the range of approximately 3 to 5 minutes. The power flows are as follows:
Pedal 132 wheel 106 (Energy E-103)
UCAP/BAT MGl ^ wheel 106 (Energy E-109b)
UCAP/BAT MG2 wheel 106 (Energy E-109a)
Kinetic Energy Harvesting
[0061] Power flows for energy harvesting are shown in Fig. 7. Energy harvesting mode is typically employed when riding on flat or downhill surface and the user stops pedaling. Pedals 132 and front sprocket 3 are disengaged by front sprocket ratchet 2 because the relative rotation is CCW. Rear sprocket 12 is able to transfer wheel rotation to front sprocket 3 by means of chain or belt 13. Front sprocket 3 is thereby driven in CW direction, MGl and MG2 also rotate CW and charge UCAP 111a and BAT 111b. The driven rotation of MGl and MG2 may create significant drag, thereby slowing down the light vehicle. The power flows are as follows:
Wheel 106 MGl ^ UCAP/BAT (Energy E-106b)
Wheel 106 MG2 UCAP/BAT (Energy E-106a)
[0062] Note that in an alternative embodiment of the energy harvesting mode, either MGl or MG2, or both MGl and MG2, may be connected to harvest the kinetic energy. Controller 122 is configured to determine whether to connect MGl, MG2 or both based on the amount of available kinetic energy (depending on the speed of the light vehicle) and the energy storage levels of UCAP 111a and BAT 111b.
[0063] Table 2 shows a summary of the usage cases described above, including typical values of the torques and cadence (RPM) for each case.
Table 2
[0064] Fig. 8 is a schematic diagram of a flow control method according to the present disclosure. In Fig. 8, the axle cadence measured by torque and cadence sensor 11 is designated by the symbol C, and the torque measured by torque and cadence sensor 11 is designated by the symbol T. The torque threshold equivalent to user-defined effort level input S-110 is designated by the symbol T2. A lower torque threshold Tl is calculated by control unit 110 and is given by Tl = kl.T2, where kl is a number between 0.5 and 0.9, with a preferred value of 0.7. An upper torque threshold T3 is calculated by control unit 110 and is given by T3 = k3.T2, where k3 is a number between 1.1 and 1.5, with a preferred value of 1.3. Note that optimum values of kl and k3 will depend on power/torque/rpm
characteristics of the motors. Control unit 110 may also be configured to vary the values of kl and k3 depending on the charging states of UCAP 111a and BAT 111b.
[0065] In step 70 the flow control method starts, and in step 72 the method determines whether C is zero (crank axle 1 is stationary). If so, and if T is greater than zero (step 74), then the cold start mode is entered in step 76. If C is greater than zero in step 72 (crank axle 1 is rotating), and if T is zero in step 78 (no torque required), then the energy harvesting mode is entered in step 80. If T is greater than zero in step 78, but T is not greater than Tl in step 82, then the soft coasting mode is entered in step 84. If T is greater than Tl in step 82, but T is not greater than T2 in step 86, then the hard coasting mode is entered in step 88. If T is greater than T2 in step 86, but T is not greater than T3 in step 90, then the soft cruising mode is entered in step 92. If T is greater than T3 in step 90, then the hard cruising mode is entered in step 94. The method ends at step 96, but returns to start again at step 70, so that the operating conditions of the light vehicle are continuously checked to determine whether a change in the power flow mode is required.
[0066] Although the present invention has been described in relation to particular embodiments thereof, it can be appreciated that various designs can be conceived based on the teachings of the present disclosure, and all are within the scope of the present disclosure.