Power management system and method

Abstract

An electric heavy-duty vehicle having a system for managing regenerative braking power when the electric heavy-duty vehicle goes up and down a downhill by managing the speed of the electric heavy-duty vehicle, the system includes an electric motor, a vehicle control unit including a torque management system, a speed controller operatively connected with the torque management system, and an energy management system operatively connected with the torque management system. A battery component is disposed on the electric heavy vehicle, and the battery component is operatively connected with the torque management system.

Description

Technical Field

[0001] The present disclosure relates to a system and method for managing the regenerative braking power of an electric vehicle (such as a heavy truck, tractor-trailer, bus, etc.) while descending a downhill driving surface by managing the vehicle's speed. The present disclosure relates to a system and method for managing the speed of an electric vehicle that utilizes an electronic controller to set a speed target and manage torque to meet the speed target. The present disclosure further relates to a method for reducing the incidence of a battery component of an electric vehicle reaching a 100% state of charge while traveling on a downhill driving surface by managing the regenerative braking power. Background Art

[0002] In electric vehicles, voltage is supplied to the motor from a battery. This voltage provides an electric current that is transmitted through a coil of copper wire located on the motor's rotating armature (i.e., rotor).

[0003] The speed of an electric motor refers to the revolutions per minute of the rotor operatively associated with the motor. Torque is one factor that influences vehicle speed. When applied to electric vehicle motors, torque is the product of the rotational force applied to the rotor operatively associated with the motor, multiplied by the distance that force travels. Torque is proportional to the voltage of the electricity transmitted from the battery to the motor and the associated current transmitted to the rotor operatively associated with the motor.

[0004] The power of an electric motor is the product of torque and rotor speed. Initially, the speed of the motor (i.e., the speed of the rotor) increases as the torque increases. However, as the rotor speed increases, some of the power generated by the rotor can be transmitted back in the opposite direction through the copper wire coil, reacting against the current supplied by the battery. This force is called back EMF (electromotive force) and is transmitted back to the battery.

[0005] The back EMF transmitted back to the battery increases as the rotor speed increases. The greater the back EMF, the more forward current flow to the rotor is impeded, and thus the greater the reduction in torque. Therefore, at higher motor speeds, the net current flow, and therefore the net or effective torque, decreases due to the increased back EMF impeding forward current flow.

[0006] Back EMF is responsible for the regenerative braking of electric vehicles. When the driver of an electric vehicle fully releases the accelerator pedal, the battery stops supplying voltage. Therefore, no DC power is transmitted to actuate the rotor.

[0007] When the accelerator pedal of an electric vehicle is fully released, no current is drawn to propel the rotor. Nevertheless, for a period of time, as the vehicle coasts, the rotor will continue to rotate. This rotation is due to mechanical force transferred back to the rotor by the vehicle's rotating wheels. Due to the vehicle's momentum, the wheels will continue to turn for a period of time after the accelerator pedal is released. The mechanical force generated by the rotor can then be converted into electricity. This electricity can be transferred back to the battery, thereby recharging the battery to a certain extent. This process is referred to by those skilled in the art as regenerative braking.

[0008] In the absence of any current flowing from the battery to the rotor, the back EMF generated by the spinning rotor can be transferred unimpeded back to the battery, thereby increasing the battery's state of charge. This regenerative braking process can continue until all of the vehicle's kinetic energy has been dissipated due to friction between the vehicle's wheels and the driving surface, as well as other potential external factors.

[0009] Thus, regenerative braking involves transferring power back to the battery in an electric vehicle, thereby recharging the battery and extending the vehicle's range. Regenerative braking occurs automatically in an electric vehicle after the accelerator pedal is fully or partially released.

[0010] However, if the battery in the electric vehicle is fully or nearly fully charged (i.e., 100% state of charge), it may no longer be possible to dissipate the electric vehicle's kinetic energy through regenerative braking. In this case, wheel braking may be required to slow or maintain the vehicle's speed. This situation is particularly problematic in electric heavy-duty trucks, as the size of the wheel brakes on electric heavy-duty trucks may not be sufficient to effectively control the vehicle's speed when traveling on long downhill driving surfaces. Summary of the Invention

[0011] An electric heavy-duty vehicle has a system for managing regenerative braking power by managing the speed of the electric heavy-duty vehicle when the electric heavy-duty vehicle descends a downhill slope. The system includes an electric motor, a vehicle control unit including a torque management system, a speed controller operatively connected to the torque management system, and an energy management system operatively connected to the torque management system. A battery unit is provided on the electric heavy-duty vehicle and is operatively connected to the torque management system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram of the energy management system of the electric vehicle described in this article. DETAILED DESCRIPTION

[0013] The following disclosure relates to electric vehicles, such as heavy trucks, and includes embodiments of systems and methods for managing regenerative braking power by managing the speed of the electric vehicle while descending on a downhill driving surface. The disclosure further relates to an electric vehicle including embodiments of a method for significantly reducing the occurrence of a battery component of the electric vehicle reaching a 100% state of charge while traveling on a downhill driving surface by managing regenerative braking power.

[0014] For the purpose of clearly describing the components, features and method steps discussed throughout this disclosure, some frequently used terms will now be defined. The term "motor" used throughout this disclosure includes both direct current (DC) and alternating current (AC) vehicle motors, unless otherwise stated. The term "motor" should be understood to include all components commonly found in current electric vehicles, either DC or AC. Such components may include rotors, shafts, and stators, among others. In the case where a system according to the present disclosure includes an AC motor, the term "motor" also includes an inverter. The term "electric heavy truck" used throughout this disclosure refers to a truck that includes an electric motor and has a weight limit of at least 20,000 pounds.

[0015] An electric heavy-duty truck may require power dissipation to control the speed of the electric heavy-duty truck on a downhill driving surface. The following graph depicts the approximate amount of power used by an electric heavy-duty truck loaded to 80,000 pounds to maintain a substantially constant speed while traveling on a 6% downhill driving surface:

[0016] curve Figure 1

[0017] Like a curve Figure 1 As shown in , as the speed of the electric heavy-duty truck increases, an increased amount of power, and therefore negative torque, may be required to maintain a substantially constant speed of the electric heavy-duty truck on a 6% downhill driving surface.

[0018] In electric vehicles, this type of power dissipation can be achieved through regenerative braking. As the state of charge of an electric vehicle's battery increases, the battery's ability to accept power decreases. At the indicated states of charge, a typical battery can accept the amounts of power listed in the table below for 30 seconds.

[0019] Table 1

[0020] As shown in Table 1, as the battery reaches a higher state of charge, the battery's ability to accept power provided by regenerative braking decreases.

[0021] Batteries in electric vehicles can accept increased amounts of power in shorter periods of time. The table below lists the maximum power acceptance over ten seconds for the same battery as above at the indicated states of charge.

[0022] Table 2

[0023] Because electric heavy-duty trucks may not have retarders like trucks with internal combustion engines, and the size of the wheel brakes of electric heavy-duty trucks may not be able to control the speed of the electric heavy-duty truck on large downhill driving surfaces, and although the electric heavy-duty truck can be decelerated by regenerative braking, once the battery associated with the electric heavy-duty truck reaches the maximum state of charge, the wheel brakes on the electric heavy-duty truck may comprise the only way to decelerate the electric heavy-duty truck. However, as previously mentioned, the size of the wheel brakes of the electric heavy-duty truck may not be able to adequately dissipate energy when traveling on a downhill driving surface, resulting in insufficient speed management capabilities of the electric heavy-duty truck. These problems may exist in electric vehicles other than electric heavy-duty trucks. The embodiments disclosed herein can be used in electric vehicles other than electric heavy-duty trucks, sometimes with appropriate modifications.

[0024] Another negative impact can be overcharging of the battery when the battery of an electric heavy truck reaches its maximum state of charge while traveling on a downhill driving surface. This overcharging can lead to exceeding the thermal limits of the battery cells and ultimately leading to potential battery failure.

[0025] According to the embodiments disclosed herein, regenerative braking power management can be achieved by managing torque in a manner that substantially avoids situations in which the battery in the electric heavy-duty truck reaches a 100% state of charge and is therefore no longer able to accept energy generated by regenerative braking, as described above. By reducing the occurrence of the battery in the electric heavy-duty truck reaching a 100% state of charge, the embodiments described herein enable the driver of the electric heavy-duty truck to maintain a substantially constant vehicle speed when traveling on a downhill driving surface.

[0026] refer to Figure 1 , an energy management system for an electric heavy-duty truck is shown, including embodiments of a system and method for managing regenerative braking power when descending on a downhill driving surface by managing the speed of the electric heavy-duty truck. The electric heavy-duty truck may include a vehicle control unit (VCU) disposed on the electric heavy-duty truck. The VCU may include a torque management system (TMS) and an energy management system (EMS). The TMS and EMS may be communicatively and operatively connected to each other.

[0027] In some conventional VCUs, the TMS is constrained only by the power limit signaled by the EMS. Power is the product of torque and speed. Therefore, for a given speed, the TMS can modify its torque request in such a way that the power output remains within the power limit signaled by the EMS.

[0028] When the driver applies the accelerator pedal and the power limit is reached, the TMS can reduce the torque command to remain within the power limit signaled by the EMS. However, when the vehicle is traveling on a downhill driving surface, due to the force of gravity acting on the vehicle, negative torque may be required to maintain a substantially constant speed of the vehicle. Therefore, according to an embodiment of the present disclosure, the TMS can request negative torque when the electric heavy-duty truck is descending on a downhill driving surface.

[0029] The VCU of a system as described herein may include a speed controller for identifying a maximum speed. Such a speed controller may be communicatively and operatively connected to the TMS. The speed controller of the present disclosure may transmit a signal to the TMS identifying the maximum speed. The TMS of the present disclosure may then calculate a target torque that complies with both the maximum speed and the power limit signaled by the EMS. By keeping the torque request substantially within both the speed and power limits, back EMF may be effectively managed when traveling on a downhill driving surface. Effective management of back EMF may reduce situations in which an electric heavy-duty truck traveling on a downhill driving surface loses regenerative braking capability due to the batteries on the electric heavy-duty truck reaching a maximum state of charge.

[0030] Thus, according to the embodiments described herein, an electric heavy-duty truck can actively decelerate when encountering a downhill driving surface by requesting a predetermined level of negative torque that complies with the power limits communicated by the EMS and also complies with the speed limits communicated by the speed controller, as described herein. In this manner, the systems and methods of the present disclosure can effectively manage regenerative braking power, thereby allowing an electric heavy-duty truck to maintain a substantially constant speed while traveling on a downhill driving surface by substantially avoiding a 100% state of charge of the battery on the electric heavy-duty vehicle.

[0031] Embodiments may include an electric motor provided on an electric heavy-duty vehicle. The electric motor may be communicatively and operatively connected to the TMS. The electric motor may be a DC motor or an AC motor. Those skilled in the art will readily understand the components of modern DC and AC motors used in electric vehicles, including electric heavy-duty trucks.

[0032] The VCU of the present disclosure may include an EMS. The EMS may be communicatively and operatively connected to the TMS. The EMS may transmit a signal to the TMS indicating a maximum power output to be adhered to. In an embodiment, the speed of the electric heavy-duty truck may be reduced in a manner corresponding to a reduction in the maximum power output of the electric motor.

[0033] Embodiments may include a battery assembly disposed on an electric heavy-duty vehicle. The battery assembly may be communicatively and operatively connected to a transmission management system (TMS). The battery assembly may transmit a signal to the TMS identifying a state of charge of the battery assembly and a maximum power accepted by the battery assembly. In embodiments, when the maximum power accepted by the battery assembly decreases, regenerative braking power may be correspondingly reduced.

[0034] Embodiments may include a speed controller that can calculate the maximum speed of the electric heavy vehicle such that a corresponding back EMF can be effectively maintained in a manner that significantly reduces overcharging of the battery.

[0035] The TMS of the present disclosure may calculate another negative target torque value upon receiving a signal transmitted by at least one of the speed controller, the EMS, and the battery component. The TMS of the present disclosure may transmit a command signal to the motor to submit such a negative target torque value.

[0036] Embodiments may further include a set of sensors communicatively and operatively connected to the speed controller. The sensors may determine the slope of a surface on which the electric heavy-duty vehicle is traveling. The sensors may transmit a signal to the speed controller identifying a change in the slope of the surface. The sensors may detect a downhill driving surface and may transmit information regarding the angle of the downhill driving surface to the speed controller.

[0037] Embodiments may further include a display component communicatively and operatively connected to the TMS. Such a display component may include an electromagnetic wave transmitter that transmits electromagnetic waves to the driver of the electric heavy-duty truck when the TMS requests negative torque when traveling on a downhill driving surface. Embodiments may further include an auditory component. Such an auditory component may include a longitudinal wave transmitter that may be configured to transmit a longitudinal wave when the TMS requests negative torque when traveling on a downhill driving surface. According to such embodiments, the properties of the electromagnetic wave and the associated longitudinal wave may be changed in a manner corresponding to the amount of negative torque requested by the TMS.

[0038] Embodiments may be utilized in conjunction with methods for managing regenerative braking power in an electric heavy-duty truck by managing vehicle speed when the electric heavy-duty truck is descending a downhill driving surface. According to such embodiments, a speed controller may transmit a signal to a TMS identifying a maximum motor speed. The EMS may transmit a signal to the TMS identifying a maximum power output of the electric heavy-duty truck's motor. The battery unit may transmit a signal to the TMS identifying a state of charge of the battery unit and a maximum power acceptance of the battery unit.

[0039] In an embodiment, upon receiving a signal transmitted by at least one of the speed controller, the EMS, and the battery component, the TMS may calculate another negative target torque value. Upon calculating the other target torque value, the TMS may transmit a command signal to the electric motor to submit the target negative torque value.

[0040] In an embodiment, the maximum power acceptance of the battery component may decrease as the state of charge of the battery component increases.

[0041] In an embodiment, the maximum motor speed may decrease as the state of charge of the battery component increases.

[0042] In an embodiment, the maximum power output of the electric motor may decrease as the state of charge of the battery component increases.

[0043] In an embodiment, the speed of the electric heavy truck may be reduced in a manner corresponding to a reduction in the maximum power output of the electric motor.

[0044] In an embodiment, regenerative braking power may be reduced in a manner correlated to a reduction in the maximum power acceptance of the battery component.

[0045] In an embodiment, such a method may further include providing a set of sensors disposed on the electric vehicle and communicatively and operatively connected to the speed controller. The sensors may determine the slope of the surface on which the electric heavy-duty truck is traveling. The sensors may transmit a signal to the speed controller identifying a change in the slope of the surface. The sensors may detect a downhill driving surface and may transmit information regarding the angle of the downhill driving surface to the speed controller. According to such an embodiment, the speed controller may determine an appropriate maximum speed based on the data received from the sensors.

[0046] Embodiments disclosed herein may be used in conjunction with a method for substantially eliminating the occurrence of a battery component of an electric heavy-duty truck reaching a 100% state of charge when traveling on a downhill driving surface by managing regenerative braking power. According to such embodiments, the display component may include an electromagnetic wave transmitter that transmits electromagnetic waves when the state of charge of the battery component exceeds 80%.

Claims

1. An electric heavy-duty vehicle having a system for managing regenerative braking power when the electric heavy-duty vehicle descends a downhill slope by managing the speed of the electric heavy-duty vehicle, the system comprising: an electric motor, the electric motor being provided on the electric heavy-duty vehicle; a vehicle control unit disposed on the electric heavy vehicle and operatively connected to the electric motor, wherein the vehicle control unit comprises: Torque management system, a speed controller operatively connected to the torque management system, and an energy management system operatively connected to the torque management system; as well as A battery component is disposed on the electric heavy vehicle and is operatively connected to the torque management system.

2. The electric heavy vehicle according to claim 1, characterized in that: The electric motor is a DC motor.

3. The electric heavy-duty vehicle according to claim 1, characterized in that: The electric motor is an AC electric motor.

4. The electric heavy vehicle according to claim 1, further comprising: A set of sensors is disposed on the electric heavy vehicle and is operatively connected to the speed controller.

5. The electric heavy vehicle according to claim 1, further comprising: A display component is provided on the electric heavy vehicle and is operatively connected to the torque management system.

6. The electric heavy-duty vehicle according to claim 5, characterized in that: The display component includes an electromagnetic wave transmitter, which is provided on the electric heavy vehicle and is operatively connected to the torque management system.

7. The electric heavy vehicle according to claim 5, further comprising: An auditory component includes a longitudinal wave transmitter provided on the electric heavy vehicle.

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