A System for Managing Power in a Vehicle and Method Thereof

FIELD OF THE INVENTION

[001] The present invention relates to a vehicle using electric power and more particularly to power management systems and methods for vehicles such as mild hybrid vehicles and the like.

BACKGROUND OF THE INVENTION

[002] 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. The electric machine acts as motor supplying power-assist to the prime mover when required.

[003] Conventionally, mild hybrid vehicles have a start-stop system, a battery and an electric engine as a prime mover. It may also include an Integrated Starter Generator (ISG). The ISG is capable of working both ways: a power generation mode and a motoring mode. In the power generation mode, the battery may be charged by the ISG which operates as a generator during regenerative braking. Alternatively, the battery may be charged by an alternator coupled to the prime mover of the vehicle. The ISG may be used to start the vehicle and assist the internal combustion engine when it needs additional power during acceleration.

[004] With reference to fully hybrid or electric vehicles, regenerative braking is the ability of the vehicle to transform kinetic energy (or motion) into electrical energy, which is then used to charge a battery of the vehicle. In other words, when the foot is taken off the accelerator pedal, the regenerative braking system kicks in to automatically charge the battery. That means a regenerative braking system essentially extends the usable range of an electric or hybrid vehicle, having a significant impact on the viability of an electric drivetrain.

[005] For example, when the vehicle is to be slowed down or halted while being driven at a speed of about 45 mph, the foot is taken off the accelerator pedal to allow coasting and electricity stops flowing form the battery pack of the vehicle to the motor. The vehicle does not come to an immediate, screeching halt though. Since the vehicle is still in momentum, it will continue to coast until that kinetic energy is gradually bled away (from friction, air drag, etc.) That’s where the regenerative braking system of the vehicle kicks in. It converts the vehicle’s electric motor into an electrical generator driven by the vehicle’s wheels, which then begins sending charge back into the electric vehicle’s batteries. [006] On the other hand, in mild hybrid vehicles, the engine may be turned- off during coasting, braking, etc., and may be restarted quickly with the help of the electric machine providing hybrid assist. Mild hybrid vehicles, unlike a full hybrid vehicle, can only travel short distances at low speeds solely on electric power. However, a mild hybrid or a semi-hybrid vehicle never operates as an electric vehicle. They do not have an electric-only mode of propulsion. The electric machine allows the internal combustion engine (ICE) to turn off when coasting or braking, thereby eliminating the belt drives that the ICE requires to run certain components. It also powers the more robust and demanding electrical architectures that modern vehicle technologies require.

[007] 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 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.

[008] The hybrid-assist provides additional power 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.

[009] In one known prior art, the problem of higher battery discharge has been addressed by charging the battery during regenerative braking at only higher RPMs, while the brake is being pressed. However, it is not feasible to reach to such high engine RPM often especially in city driving conditions. Thus, the mechanical energy gets wasted as regenerative braking fails to happen because high engine RPM is never reached in city driving conditions. Thus, a huge amount of torque gets wasted due to this.

[010] In another known prior art, a control system is provided for regenerative braking. The system controls the valve-timing in the internal combustion engine based upon vehicle parameters such as deceleration torque required, ISG torque capacity, engine torque capacity, and the like. The vehicle parameter data is sensed/monitored by a sensing mechanism and communicated to the system. Accordingly, the system changes the compression torque applied by the ISG by varying the valve-timing. The ISG torque capacity is calculated based on ISG speed & temperature, battery state of charge (SOC) and temperature and the electrical load of the vehicle. The engine torque capacity is calculated from engine speed and operating range of variable valve timing mechanism (VVT). However, this control system is directed to and suitable for fully hybrid vehicles only.

[011] In another known method in prior art, as the brake is operated, the clutch load torque is calculated as a sum of ISG load torque and engine friction torque, which is then compared with the wheel torque. Regenerative braking is enabled only when the wheel load torque is greater than the clutch load torque by a threshold thereby preventing the abnormal engine OFF condition during regenerative braking. The regenerative braking is not enabled if the state of power electronics is not normal, the engine friction is not stabilized, the clutch state is open, or the engine speed or battery SOC is less than a predefined value. The regenerative current/charging provided in this method is very limited. The battery does not get sufficient regenerative charging and a lot of kinetic energy available for regenerative charging remains underutilized and ultimately wasted.

[012] In another known method in prior art, regeneration is enabled only after a certain high rpm speed value of the engine of the vehicle is achieved. As mentioned earlier, in this method the battery may not be charged at all during city driving conditions which may sometimes include hours of driving. [013] Thus, there is a need in the art for a power management system and method for a vehicle, which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION

[014] In one aspect, the present invention is directed at a system for managing power in a vehicle. The system includes a speed sensing unit, a brake sensing unit and a control unit. The speed sensing unit measures and communicates speed values of the vehicle. The brake sensing unit senses and communicates a brake status of a brake of the vehicle. The brake status may be one of an ON status when the brake is applied and an OFF status when the brake is not applied to the vehicle. The control unit is configured for switching the vehicle between a plurality of vehicle modes of the vehicle. The plurality of vehicle modes includes a regeneration mode and a nonregeneration mode. The control unit is configured to switch the vehicle from the non-regeneration mode into the regeneration mode when one of the speed values of the vehicle is greater than a predefined threshold speed value, time elapsed since a last switch is more than a predefined cool-off time and the brake status is the ON status. During the regeneration mode, a battery of the vehicle is charged using a regeneration current with a predefined regulated voltage greater than a normal charging voltage. The vehicle is said to be in the non-regeneration mode when not in the regeneration mode, that is when no regeneration current is generated.

[015] In an embodiment, the control unit is configured to switch the vehicle from the regeneration mode into the non-regeneration mode when the vehicle has been in the regeneration mode for a predefined regeneration time.

[016] In an embodiment, the control unit is configured to switch the vehicle into the non-regeneration mode when one of the speed values of the vehicle falls below a predefined exit speed value.

[017] In various embodiments, the speed values include a motor speed of a motor of the vehicle and a crankshaft speed of a crankshaft of the vehicle.

[018] In an embodiment, the speed sensing unit and the brake sensing unit are configured to continuously measure and communicate the speed values and the brake status to the control unit, reshpectively.

[019] In another aspect, the present invention is directed at a method for managing power in a vehicle. The method comprises steps of determining speed values of the vehicle, determining a brake status of a brake of the vehicle, switching the vehicle between a regeneration mode and a nonregeneration mode, and charging a battery of the vehicle during the regeneration mode via a regeneration current. The charging is performed with a predefined regulated voltage which is greater than a normal charging voltage. The step of determining speed values of the vehicle is performed by a speed sensing unit and includes continuously determining the speed values of the vehicle. The speed values include a motor speed of a motor of the vehicle and a crankshaft speed of a crankshaft of the vehicle. The step of determining the brake status of the brake is performed using a brake sensing unit and includes continuously determining the brake status of the brake of the vehicle. The step of switching is performed by a control unit and includes switching the vehicle between the regeneration mode and the nonregeneration mode depending upon the speed values of the vehicle, the brake status and an elapsed-time since a last switch. The step of charging the battery is performed using the control unit and includes charging the battery of the vehicle during the regeneration mode, via a regeneration current with a predefined regulated voltage greater than a normal charging voltage.

[020] In an embodiment, the step of determining the speed values of the vehicle comprises determining a motor speed of a motor of the vehicle and a crankshaft speed of a crankshaft of the vehicle.

[021] In an embodiment, the method comprises switching the vehicle into the regeneration mode when one of the speed values is more than a predefined threshold speed value, the brake status is an ON status, and the elapsed- time is greater than a predefined cool-off time. The brake status is the ON status when a brake of the vehicle is being applied to the vehicle. [022] In an embodiment, the method comprises switching the vehicle into the non-regeneration mode when one of the speed values is less than a predefined exit speed value.

[023] In an embodiment, the method comprises switching the vehicle into the non-regeneration mode when the brake status is an OFF status. The brake status is the OFF status when the brake is not being applied to the vehicle.

[024] In an embodiment, the method comprises switching the vehicle into the non-regeneration mode when the vehicle has been in the regeneration mode for a predefined regeneration time.

[025] In an embodiment, the method comprises communicating continuously the speed values and the brake status to the control unit.

[026] In an embodiment, the method comprises calculating the elapsed-time since the last switch via the control unit, wherein during the last switch the vehicle was switched from the regeneration mode into the non-regeneration mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[027] 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 a vehicle, in accordance with an embodiment of the invention.

Figure 2 is a flow chart illustrating a method for managing power in the vehicle, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[028] The present invention relates to a system and a method for managing power in a vehicle. More particularly, the present invention relates to a power management system and a method in a mild hybrid vehicle using electric power.

[029] Figure 1 illustrates a vehicle 150, in accordance with an embodiment of the invention. For example, the vehicle 150 may be a mild hybrid twowheeler or a three-wheeler vehicle. The vehicle 150 has a motor 152 as a prime mover, a brake 154, a battery 156, and a crank shaft 158. The motor 152 may be an internal combustion engine and is the prime mover for powering the vehicle 150. The battery 156 provides electric power to the electric architecture of the vehicle 150 such as turn signals, head lamps, horn, display, and the like. Additionally, the battery 150 also provides additional power (power assist) to the prime mover and in turn to the vehicle 150 when required. For example, during start-stop, hill-climb, higher acceleration and the like.

[030] Figure 1 also illustrates a system 100 for managing power in the vehicle 150 in accordance with an embodiment of the invention. The system 100 comprises a speed sensing unit 112 for measuring and communicating speed values of the vehicle 150, a brake sensing unit 114 for sensing and communicating a brake status of the brake 154 of the vehicle 150, and a control unit 1 16 for switching the vehicle 150 between a plurality of vehicle modes of the vehicle 150. The brake status is one of an ON status when the brake 154 is applied and an OFF status when the brake 154 is not applied to the vehicle 150. The control unit 116 is configured for switching the vehicle 150 between the plurality of vehicle modes. The plurality of vehicle modes is one of a regeneration mode and a non-regeneration mode. During the regeneration mode, the battery 156 of the vehicle 150 is charged using a regeneration current when the vehicle 150 is decelerating during braking, coasting and the like. The vehicle 150 is said to be in a non-regeneration mode when it is not in the regeneration mode. The control unit 116 is configured to switch the vehicle 150 from the non-regeneration mode into the regeneration mode when one of the speed values of the vehicle 150 is greater than a predefined threshold speed value, time elapsed since a last switch is more than a predefined cool-off time and the brake status is the ON status. While in the regeneration mode, the battery (156) of the vehicle 150 is charged using a regeneration current with a predefined regulated voltage greater than a normal charging voltage. The normal charging voltage is about 14V to 15V and more precisely, the normal charging voltage is 14.3V to 14.6V. In an embodiment, the predefined regulated voltage is greater than the normal charging voltage by about 10% to 70% of the normal charging voltage. In another embodiment, the predefined regulated voltage is greater than the normal charging voltage by about 30% to 50% of the normal charging voltage.

[031] In various embodiments, the speed values include a motor speed of the motor 152 of the vehicle 150 and a crankshaft speed of the crankshaft 158 of the vehicle 150. The motor speed is measured in revolutions per minute (RPM). For example, an idling rpm for the motor may be 1200 rpm. In an embodiment, the control unit 116 is configured to switch the vehicle 150 from the non-regeneration mode into the regeneration mode when the motor speed is greater than a predefined threshold speed value. The predefined threshold speed value is greater than the idling speed of the vehicle 150. For example, the predefined threshold speed value is 5-10% higher than the idling speed which is 1200 rpm. The predefined threshold speed value is 1260-1320 rpm. In another example, the predefined threshold speed value is about 8-20% higher than the idling speed. The predefined threshold speed value is 1296-1440 rpm.

[032] In an exemplary embodiment, the vehicle 150 includes a permanent magnet machine (not shown) mechanically coupled to the crankshaft 158 of the vehicle 150. The speed sensing unit 112 is used to measure and communicate the crankshaft speed of the crankshaft 158. The control unit 116 is configured to control and monitor the operation of the permanent magnet machine. During the regeneration mode, the electrical energy generated from the permanent magnet machine is used to charge the battery 156 of the vehicle 150.

[033] In an embodiment, the control unit 116 is configured to switch the vehicle 150 from the regeneration mode into the non-regeneration mode when the vehicle 150 has been in the regeneration mode for a predefined regeneration time. The predefined regeneration time is chosen depending upon the quality, age, size and capacity of battery 156. The predefined regeneration time may be in the order of a few seconds or few minutes. The predefined regeneration time is the maximum time for which the battery 156 is charged during the regeneration mode using the higher predefined higher voltage. This ensures safe charging and gives the battery 156 time to cool-off and thus increase efficiency and age of the battery 156. In an exemplary embodiment, the predefined regeneration time is about 2-4 seconds. [034] In an embodiment, the control unit 116 is configured to switch the vehicle 150 into the non-regeneration mode when one of the speed values of the vehicle 150 is less than a predefined exit speed value. The predefined exit speed value is the minimum speed at which the vehicle 150 may charge the batteries 156 using the regeneration current. In various exemplary embodiments, the predefined exit speed value is about the same as the idle speed of the motor 152 and less than the predefined threshold speed value. The predefined exit speed value may be about 90-105% of the idle speed.

[035] In an embodiment, the speed sensing unit 112 and the brake sensing unit 114 are configured to continuously measure and communicate the speed values and the brake status to the control unit 1 16, respectively.

[036] In an exemplary embodiment, the vehicle 150 includes an integrated starter generator (ISG) unit. During the regeneration mode, the ISG unit operates in a generating mode to charge the battery 156 with a predefined regulated voltage which is greater than the regulated voltage during normal charging mode. During the non-regeneration mode, the control unit 116 is configured to operate the ISG in a motoring mode, wherein the ISG is available to provide assistance in the form of additional power to the motor 152 of the vehicle 150.

[037] Figure 2 is a flow chart illustrating a method 200 for managing power in the vehicle 150, in accordance with an embodiment of the invention. The method 200 includes method steps 202, 204, 206 and 208. At step 202, the method 200 includes determining continuously speed values of the vehicle 150. In various embodiments, the speed values include a motor speed of a motor 152 of the vehicle and a crankshaft speed of a crankshaft 158 of the vehicle 150. The speed value determination is performed by the speed sensing unit 112. At step 204, the method 200 includes determining continuously a brake status of a brake 154 of the vehicle 150. The brake status determination is performed by the brake sensing unit 114. At step 206, the method 200 includes switching the vehicle 150 between a regeneration mode and a non-regeneration mode depending upon the speed values of the vehicle 150, the brake status and an elapsed-time since a last switch. The switching between the modes of the vehicle 150 is performed by control unit 116. At step 208, the method 200 includes charging a battery 156 of the vehicle 150 during the regeneration mode using a regeneration current. The charging is performed by the control unit 116 with a predefined regulated voltage greater than a normal charging voltage.

[038] In an embodiment, the method 200 includes a step 210. At step 210, the method calculates the elapsed time since when the last switch between the regeneration mode and the non-regeneration mode happened for the vehicle 150. The elapsed time is calculated from the last instant the vehicle 150 was switched from the regeneration mode to the non-regeneration mode. The elapsed time is the time duration for which the vehicle 150 has not been in the regeneration mode and the battery 156 is not being charged using the regeneration current.

[039] In an embodiment, the method step 202 of determining the speed values includes determining the motor speed of the motor 152 of the vehicle 150 and the crankshaft speed of the crankshaft 158 of the vehicle 150.

[040] In an embodiment, the method 200 includes step 212. At step 212, one of the speed values including the motor speed and the crank shaft speed are compared with a predefined threshold speed value. The predefined threshold speed value is greater than the idling speed of the vehicle 150. For example, the predefined threshold speed value is 5-10% higher than the idling speed. In another example, the predefined threshold speed value is about 8-20% higher than the idling speed.

[041] In an embodiment, the method 200 includes step 214. At step 214, the brake sensing unit 114 checks the brake status for being one of an ON status and an OFF status. The brake status is the ON status, when the brake 154 is being applied to the vehicle 150 for deceleration and the brake status is said be in the OFF status when the brake 154 is released and is no more being applied to the vehicle 150.

[042] In an embodiment, the method 200 includes step 216. At step 216, the control unit 116 compares the elapsed time calculated at step 210 with a Y1 predefined cool-off time. The predefined cool-off time depends on the quality, age, size and capacity of the battery 156. Accordingly, in various exemplary embodiments, the predefined cool-off time may be in the order of few seconds or a few minutes. The predefined cool-off time is the minimum time that the vehicle should wait before re-entering the regeneration mode to charge the batteries 156 using the regeneration current so that the battery can cool down for efficient charging.

[043] In an embodiment, the step 206 includes switching the vehicle 150 into the regeneration mode when one of the speed values is more than a predefined threshold speed value, the brake status is the ON status, and the elapsed-time is greater than the predefined cool-off time.

[044] In an embodiment, the method 200 includes step 218. At step 218, the method 200 includes comparing one of the speed values including the motor speed and the crankshaft speed of the vehicle 150 with a predefined exit speed value. The control unit 116 switches the vehicle 150 into the nonregeneration mode when and if one of the speed values is less than a predefined exit speed value. The predefined exit speed value is the minimum speed at which the vehicle 150 may remain in the regeneration mode for charging the battery 156 using the regeneration current. In various exemplary embodiments, the predefined exit speed value is more than the idle speed and less than the predefined threshold speed value. The predefined exit speed value may be about 90-95% of the idle speed.

[045] In an embodiment, the step 206 includes switching the vehicle 150 into the non-regeneration mode if and as soon as the brake status, which is continuously being determined at the step 202, is the OFF status.

[046] In an embodiment the method 200 includes step 220. At step 220, the method includes comparing the elapsed time since the last switch (from the non-regeneration mode to the regeneration mode) with a predefined regeneration time. As a result, the elapsed time since the vehicle has been in the regeneration mode is compared to the predefined regeneration mode. Subsequently, the control unit 116 puts the battery 156 on charging using the regeneration current at the method step 208, if and as long as, the elapsed time for the regeneration mode is not greater than the predefined regeneration time. The batteries 156 are charged with a predefined regulated voltage greater than the normal charging voltage. In an embodiment, the step 206 includes switching the vehicle 150 into the non-regeneration mode if and when the vehicle 150 has been in the regeneration mode for more than the predefined regeneration time.

[047] The predefined regeneration time is chosen depending upon the quality, age, size and capacity of battery 156. The predefined regeneration time may be in the order of a few seconds or few minutes. The predefined regeneration time is the maximum time for which the battery 156 is charged during the regeneration mode using the higher predefined higher voltage. This ensures safe charging and gives the battery 156 time to cool-off and thus increase efficiency and age of the battery 156. In an exemplary embodiment, the predefined regeneration time is about 2-4 seconds. In another exemplary embodiment, the predefined regeneration time is about 1 - 6 seconds.

[048] Advantageously, the system and method for managing power in the vehicle provided by the invention enables charging of the battery at lower engine rpms and thus reduces the wastage of available regeneration power and provides for maximum utilisation of the regeneration power. The invention provides more charging for the battery which has an increased availability for providing power-assist to the motor when required. The invention enables charging of the battery using the regeneration current at lower engine rpms and thus even in city like driving conditions.

[049] The invention also increases the battery charging adequacy as the entry into the regeneration mode is after a predefined cool-off time and the duration for which the vehicle remains in the regeneration mode is also controlled by the predefined regeneration time. The invention thus increases the battery life by providing enhanced battery charging. [050] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

Reference Numeral List:

SYSTEM 100

SPEED SENSING UNIT 112

BRAKE SENSING UNIT 114 CONTROL UNIT 116

VEHICLE 150

MOTOR 152

BRAKE 154

BATTERY 156

CRANKSHAFT 158