Description:FIELD OF THE INVENTION
[001] The present invention relates to systems and methods for managing power in an electrically assisted vehicle and more particularly, the invention relates to systems for electrically assisted vehicles such as two and three wheeled vehicles.

BACKGROUND OF THE INVENTION
[002] Electrically assisted vehicles or mild hybrid vehicles (also known as power-assist hybrids, Battery-Assisted Hybrid Vehicles or BAHVs) are vehicles which have a combination of an internal combustion engine as a prime mover and an electric machine. The electric machine may be a motor or a generator arranged in a parallel hybrid configuration with the Internal Combustion Engine (ICE). The electric machine acts as motor supplying power-assist to the prime mover when required.
[003] When the operator starts the ignition for a mild hybrid vehicle, the ICE working alone and independently takes some time to reach the desired RPM for moving the vehicle with desired acceleration. There is an appreciable delay in the response time of the ICE. To reduce this delay, hybrid assist is provided. The electric machine (such as an ISG) when in motoring mode, provides extra torque to the engine to reach the desired RPM faster. However, in providing hybrid assist through the ISG, a huge amount of energy is drawn from the battery which results in battery drainage.
[004] The electric machine provides additional power (hybrid-assist) to the engine not only at the start when the vehicle is first ignitioned but also helps in acceleration whenever required such as start-stop drives in the city traffic, hill climb, overtaking and the like. Particularly in city traffic, the demand and load on the hybrid assist functionality is higher since the vehicle stop-starts lot of times and requires quick acceleration more frequently. As a result, the rate at which battery gets discharged is higher than the rate of charging the battery, thereby affecting the battery life since the battery remains mostly in discharged state (below minimum SOC level), which is undesirable.
[005] In a known prior art, a method for providing hybrid assist based on predicting a driving cycle, which is based further upon identifying two driving ranges, whose data is within tolerances range of each other. A trend is identified relating to a historical driving ranges and then predicting the driving range which is in tolerance of the current driving range. The historical driving range data includes one or more distances that was driven in the previous driving cycles of the vehicle. The electric machine is operated to provide selective assistance to the engine at predetermined operating conditions which are determined by a controller based on at least in part on the predicted driving cycle, frequency of vehicle in certain operating conditions, the available energy in the energy storage device, the expected energy to be regenerated in the driving cycle. The assistance given to the engine also depends on the frequency of operating the vehicle in certain conditions, wherein the frequency is determined based on the historical data of the vehicle. The selective assistance controls the motor of the vehicle based upon one of plurality of assistance profiles. The motor is configured to provide at least one pulse assist when demand for acceleration is sensed. However, the method provided does not provide any improvement in fuel economy and there is no reduction of emissions from the vehicle.
[006] In another known prior art, a transmission control apparatus for a hybrid electric vehicle comprises a transmission that transmits a driving force of an engine to the driving wheels via a clutch and disengages the clutch during a shift. The apparatus also includes a vehicle speed detector for detecting a vehicle speed, a charge state detection unit for detecting a charge state of the battery, and an assist torque control unit that gradually restricts the assist torque of the electric motor during shifting based on the vehicle speed and the state of charge. The assist torque control unit increases the assist torque of the electric motor as the vehicle speed increases. However, it is apparent that torque loss during clutch disconnection at the time of shift causes deacceleration and a sudden shock during the time of gear shift. This causes much discomfort to a rider of the vehicle.
[007] Another known prior art discloses a power generation control device in a hybrid vehicle. The power generation control device controls the drive torque, requests a power generation amount and a power generation correction amount. The power generation control device sets a drive torque corresponding to the acceleration command. The drive torque is increased with increase in accelerator opening degree and the drive torque is gradually decreased when vehicle is running at higher speeds. The power generation amount increases and rate of change in requested power generation amount decreases with increase in accelerator opening degree. The control device gradually increases the power generation correction amount and decreases the rate of change of power generation correction amount with the increase in a difference between the current battery SOC and the target battery SOC. The control device controls the drive motor based on the drive torque and controls the power generator based on the request power generation amount and the power generation correction amount. However, as the power used by the motor is decided by the power generated, there is discomfort to the rider as motor is still running at constant speed despite the acceleration command.
[008] In yet another known prior art, a drive control system is disclosed. A required torque is calculated based on the accelerator operation amount and the engine speed. A remaining charge detection unit is used to detect the remaining charge in the battery. A determination torque is obtained based on engine torque when engine is operated in thermal efficient zone according to the remaining battery charge. A target engine and motor torque is obtained from the relationship between the required torque and the determined torque. The target motor torque is calculated based on the difference between the target engine torque and the target motor torque. An operation unit controls the operation of engine and motor based on the target engine torque and target motor torque. The power generation determination torque is calculated based on the battery state of charge (SOC) and this becomes target engine torque if required torque is less than power generation determination torque. The discharge determination torque is obtained based on the battery SOC and this becomes target engine torque if required torque is greater than discharge determination torque. But if the required torque is greater than power generation torque or less than discharge determination torque, the target engine torque is required torque itself and the motor is not operated. However, there is a problem of over over-charge and over-discharge of the battery by setting the engine operating point in the predetermined region.
[009] It is observed that in electrically assisted vehicles, when hybrid assist is introduced, lot of power is consumed from the battery and the time taken to recharge the battery is considerably increased. It also leads to the battery not getting charged at the end of a worst-case driving cycle. This can lead to battery drainage and reduced battery life and vehicle starting problems. This also affects the battery life. Further, during running condition, it is not possible to determine the battery SOC.
[010] Thus, there is a need in the art for a system and method for electrically assisted vehicles, which address at least the aforementioned problems.

SUMMARY OF THE INVENTION
[011] In one aspect, the present invention is directed at a system for managing power in an electrically-assisted vehicle. The system comprises a starter-generator unit mechanically coupled to a crankshaft of the vehicle and a controller for managing the starter-generator unit. The starter-generator unit is configured to provide an assist to the vehicle. The assist is an additional power provided to the vehicle in addition to power provided by a prime mover of the vehicle. The controller is configured to supply the assist to the vehicle via the starter-generator unit for a predetermined duration based upon a state of charge of a battery of the vehicle. The starter-generator unit receives power from a battery of the vehicle.
[012] In an embodiment, the predetermined duration is proportional to a value of the state of charge of the battery and reduces with the state of charge value. The predetermined duration is zero if the state of charge value is less than a predefined state of charge value.
[013] In an embodiment, the controller is configured to provide the assist when an operator of the vehicle activates a hybrid assist mode of the vehicle. The controller is configured to determine the state of charge of the battery.
[014] In an embodiment, the system comprises a speed sensor for measuring and communicating a prime mover speed of the prime mover of the vehicle; a brake switch for sensing and communicating a brake status of a brake of the vehicle; and a control unit configured to enable charging of the battery using a regeneration current based upon inputs from the speed sensor and the brake switch.
[015] In an embodiment, the controller is configured to charge the battery using the regeneration current from the starter-generator unit. The control unit signals the controller to charge the battery based upon the prime mover speed and the brake status.
[016] In another aspect, the invention is directed towards a method for managing power in an electrically-assisted vehicle comprising determining, via a controller, a state of charge of a battery of the vehicle; and providing, via a starter-generator unit, an assist to the vehicle for a predetermined duration. The predetermined duration is dependent upon the state of charge of the battery of the vehicle.
[017] In an embodiment, the predetermined duration is proportional to a value of the state of charge of the battery and reduces with the state of charge value. The predetermined duration is zero if the state of charge value is less than a predefined state of charge value.
[018] In an embodiment, the assist is provided when an operator of the vehicle activates a hybrid assist mode of the vehicle.
[019] In an embodiment, the method comprises sensing and communicating, via a speed sensor, a prime mover speed of a prime mover of the vehicle; sensing and communicating, via a brake switch, a brake status of a brake of the vehicle; signaling, via a control unit, the controller to charge the battery depending upon the prime mover speed and the brake status; and charging, via the controller, the battery using a regeneration current from the starter-generator unit.

BRIEF DESCRIPTION OF THE DRAWINGS
[020] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 illustrates a system for managing power in an electrically-assisted vehicle, in accordance with an embodiment of the invention.
Figure 2 is a flow chart illustrating a method for managing power in an electrically-assisted vehicle, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[021] The present invention relates to a system and method for managing power in electrically assisted vehicles. More particularly, the present invention relates to system and method for providing and managing power assist and battery charging in electrically assisted vehicles.
[022] Figure 1 illustrates a system 100 for managing power in an electrically-assisted vehicle 150, in accordance with an embodiment of the invention. For example, the electrically-assisted vehicle 150 is a two-wheeler or a three-wheeler vehicle. The electrically-assisted vehicle 150 has a prime mover 156 such as an internal combustion engine for providing power to a crankshaft 154 of the electrically-assisted vehicle 150 and also to provide traction to at least one wheel of the electrically-assisted vehicle 150.
[023] The system 100 comprises a starter-generator unit 152 and a controller 110 for managing the starter-generator unit 152. The starter-generator unit 152 is mechanically coupled to the crankshaft 154 of the vehicle 150. The starter-generator unit 152 is configured to provide an assist to the vehicle 150. The starter-generator unit 152 is a permanent magnet machine which is used to start and assist the prime mover 156. The assist is an additional power provided to the vehicle 150 in addition to power provided by the prime mover 156 of the vehicle 150.
[024] The controller 110 manages and controls the operation of the starter-generator unit 152. The controller 110 is configured to supply the assist to the vehicle 150 via the starter-generator unit 152 for a predetermined duration based upon a state of charge of a battery 160 of the vehicle 150. The battery 160 provides power to the starter-generator unit 152. The battery 160 stores electrical energy generated from the permanent magnet machine during regeneration. The battery 160 also supports starting and assisting of the prime mover 156.
[025] In an embodiment, the predetermined duration is proportional to a value of the state of charge of the battery 160 and reduces with the state of charge value. The predetermined duration is zero if the state of charge value is less than a predefined state of charge value.
[026] In an embodiment, the controller 110 is configured to provide the assist when an operator 190 of the vehicle 150 activates a hybrid assist mode of the vehicle 150. The controller 110 is configured to determine the state of charge of the battery 160. The battery 160 is directly connected to the controller 110. During running condition of the vehicle 150, when the operator 190, which is a user/driver/rider of the vehicle 150, activates the hybrid assist mode, the controller 110 checks for and determines the battery SOC (State of Charge) and executes the hybrid assist depending the battery SOC.
[027] For example, during cranking and hybrid assist activation, the controller 110 determines the battery 160 SOC. If the battery (160) SOC is greater than or equal to the predefined state of charge value, then the assist is performed for the whole of the predetermined duration. The predetermined duration is determined based upon calibration and empirical data and depends upon vehicle running condition and battery capacity and size. However, if the battery SOC is less than the predefined state of charge value, the assist is performed for less than predetermined duration. In an embodiment, the assist is performed for 80% of the predetermined duration. In another embodiment, the assist is performed for 50-75% of the predetermined duration. The predefined state of charge value may be 70-90%. In another embodiment, the predefined state of charge value is 65-75%.
[028] In an embodiment, the assist is provided based upon the following rules:
Battery SOC Assist provided for:
SOC = 100% 600J-700J for 5sec
80=