Method and system for kinetic energy recovery in a hybrid powertrain during engine shutdown

Examples of hybrid powertrain systems are provided herein. The system includes: an engine; a motor/generator (“MG”); a clutch coupled to the engine and the MG; a transmission coupled to the MG; an energy storage system connected to the MG; and a controller coupled to the engine, the MG, the clutch, the transmission and the energy storage system. The controller is configured to initiate an engine stop, allow engine torque and MG torque to reduce to zero or near zero, shift the transmission to a neutral gear, cause the MG to operate in a generator mode, thereby loading the engine to recover kinetic energy from the engine, disengage the clutch to decouple the MG from the engine, increase the speed of the MG to a target speed, and shift the transmission into gear in response to the MG reaching the target speed.

FIELD

Disclosed embodiments relate generally to hybrid powertrain control and more particularly to methods and systems for recovering energy from an internal combustion engine during shutdown to improve the overall efficiency of the hybrid powertrain.

BACKGROUND

Hybrid vehicles generally include an internal combustion engine and at least, one motor/generator (“MG”). Many hybrid vehicles use an engine start/stop feature in which a vehicle controller shuts down the internal combustion engine under certain circumstances (e.g., when the vehicle is at zero speed, such as at a stop light) to consume less fuel and reduce emissions. While such engine shutdowns reduce energy consumption in terms of fuel, restarting the engine after the shutdown consumes energy. In some vehicles, a small electric starter is used to restart the engine, but that approach is inefficient from an energy consumption standpoint, especially when the powertrain includes a large internal combustion engine and shutdowns occur frequently. Other restart approaches include closing the clutch while the vehicle is at speed under power of the MG (similar to “bump starting” the vehicle), but this approach slows the vehicle, loses energy as a result of clutch slippage and affects drivability.

Alternatively, the MG of the powertrain may be used to restart the engine. Full hybrid vehicles (also known as “strong” hybrids) have relatively large MGs which can propel the vehicle without use of the engine. During engine restart, the transmission could be placed in neutral to disconnect the MG from the final drive, making the MG available for restarting the engine. Then, the MG speed could, be decreased to zero and the clutch between the MG and engine could be closed, thereby resulting in nearly zero energy loss due to clutch slippage. The engine could then be started with the MG. This approach also results in undesirable energy consumption. As such, it is clear that further improvements in energy efficiency for hybrid vehicles using start/stop technology is needed.

SUMMARY

In one embodiment, the present disclosure provides a hybrid powertrain system, comprising: an engine; at least one motor/generator (“MG”); a clutch coupled to the engine and the at least one MG; a transmission coupled to the at least one MG; an energy storage system connected to the at least one MG; and a controller operatively coupled to the engine, the at least one MG, the clutch, the transmission and the energy storage system, the controller including a processor and a memory including instructions that when executed by the processor, cause the controller to initiate an engine stop, allow engine torque and torque associated with the at least one MG to reduce to zero or near zero, shift the transmission to a neutral gear, cause the at least one MG to operate in a generator mode, thereby loading the engine through the clutch to recover kinetic energy from the engine, disengage the clutch to decouple the at least one MG from the engine, increase a speed of the at least one MG to a target speed, and shift the transmission into gear in response to the at least one MG reaching the target speed. In one aspect of the disclosure, execution of the instructions by the processor further causes the controller to propel a vehicle using power from the at least one MG after shifting the transmission into gear. In a variant of this aspect, the vehicle is a full hybrid vehicle. In another variant, the engine is an internal combustion engine. In another variant of this aspect, initiating an engine stop includes determining based upon input from at least one sensor that power from the engine is not required to propel the vehicle. In another variant, shifting the transmission to a neutral gear decouples the at least on MG from a final drive of the vehicle. In another aspect of this embodiment, execution of the instructions by the processor further causes the controller to control the at least one MG to store energy recovered from the engine by the at least one MG in the energy storage system. In yet another aspect, the energy storage system includes a plurality of batteries.

In another embodiment, the present disclosure provides a method for recovering energy from an engine in a hybrid powertrain including at least one motor/generator (“MG”), comprising: initiating an engine stop; allowing engine torque and torque associated with the at least one MG to reduce to zero or near zero; shifting a transmission coupled to the at least one MG to a neutral gear; causing the at least one MG to operate in a generator mode, thereby loading the engine through a clutch to recover kinetic energy from the engine; disengaging the clutch to decouple the at least one MG from the engine; increasing a speed of the at least one MG to a target speed; and shifting the transmission into gear in response to the at least one MG reaching the target speed. One aspect of this embodiment further comprises propelling a vehicle using power from the at least one MG after shifting the transmission into gear, in a variant of this aspect, the vehicle is a full hybrid vehicle. In another variant, the engine is an internal combustion engine. In yet another variant, initiating an engine stop includes determining based upon input from at least one sensor that power from the engine is not required to propel the vehicle. In still a further variant, shifting a transmission to a neutral gear decouples the at least on MG from a final drive of the vehicle. Another aspect of this embodiment further comprises storing energy recovered from the engine by the at least one MG in an energy storage system connected to the at least on MG. In another aspect, the energy storage system includes a plurality of batteries.

In, still another embodiment, the present disclosure provides a hybrid powertrain system, comprising: an engine; at least one motor/generator (“MG”); a first clutch coupled to the engine and the at least one MG; a second clutch coupled between the at least one MG and a final drive; an energy storage system connected to the at least one MG; and a controller operatively coupled to the engine, the at least one MG, the first clutch, the second clutch and the energy storage system, the controller including a processor and a memory including instructions that when executed by the processor, cause the controller to initiate an engine stop, allow engine torque and torque associated with the at least one MG to reduce to zero or near zero, open the second clutch, cause the at least one MG to operate in a generator mode, thereby loading the engine through the first clutch to recover kinetic energy from the engine, disengage the first clutch to decouple the at least one MG from the engine, increase a speed of the at least one MG to a target speed, and close the second clutch in response to the at least one MG reaching the target speed.

It should be appreciated that in various embodiments the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination. Further, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying figures.

DETAILED DESCRIPTION

Referring now toFIG.1, a conceptual block diagram of a hybrid vehicle10is shown including a powertrain12having an internal combustion engine14, a clutch16, an electric machine (hereinafter referred to as a motor/generator (MG18)), and a transmission20. Vehicle10further includes an energy storage system22, a final drive24and a controller26, including a processor28and a memory30. Powertrain12may include other components and is only depicted as shown to describe the operation of the technology of the present disclosure. For example, powertrain12may include additional clutches16and/or additional MGs18. Moreover, vehicle10may be configured as a mild hybrid, a full hybrid or a plug-in hybrid. Additionally, while the description herein contemplates use of powertrain12, the teachings of the present disclosure may be used in other applications such as in a hydraulic hybrid powertrain. Finally, the teachings of the present disclosure may have application to powertrains for equipment other than vehicles.

Internal combustion engine14is mechanically coupled to MG18by clutch16. Engine14may be any type of combustion engine including, but not limited to spark-ignited engines or compression-ignited engines of any configuration, size and/or fuel type.

MG18is further mechanically coupled to transmission20, which in turn is mechanically coupled to final drive24which contains a differential that mechanically couples to a drive shaft32connecting two or more wheels34together.

MG18is electrically coupled to energy storage system22to receive electrical power from energy storage system22and to deliver electrical power to energy storage system22. Energy storage system22in some examples includes, but is not limited to, batteries such as lithium-ion, nickel-metal hydride, or lead-acid batteries. Energy storage system22may alternatively include ultracapacitors or other types of energy storage devices. InFIG.1, thick lines represent mechanical coupling, whereas thin lines represent electrical coupling, for example, via wires or wirelessly.

As indicated above, controller26includes a processor28and a memory storage device30. Processor28may be any suitable processor such as a central processing unit (CPU), state machines, system-on-chip (SoC), etc. The memory storage device30may be any suitable memory such as random access memory (RAM), read-only memory (ROM), flash memory, etc. As shown, controller26is electrically coupled to engine14, clutch16, MG18, transmission20, and energy storage device22, such that controller26may detect any input from these components as well as send operation signals to control the operation of these components.

In some examples, the components that are electrically coupled with controller26have one or more sensors (not shown) coupled thereto that take measurements which indicate the present status of the component, such as a state-of-charge (SOC) of energy storage device22, the temperature of engine14and/or its aftertreatment system (not shown), the on/off status of clutch16, among others. In some examples, such data is stored in memory storage device30of controller26such that controller26may use the stored data at any time without having to take new measurement when needed. In some examples, the data in memory storage device30is updated frequently at a constant rate, i.e., new measurements are taken at predetermined intervals, such that “freshness” of the data is maintained. Controller26in some examples has instructions, e.g., computing algorithms, stored in memory storage device30which processor28uses to perform the control process as disclosed herein.

Controller26may form a portion of a processing subsystem including one or more computing devices having non-transient computer readable storage media, processors or processing circuits, and communication hardware. Controller26may be a single device or a distributed device, and the functions of the controller may be performed by hardware and/or by processing instructions stored on non-transient machine-readable storage media. Example processors include an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), and a microprocessor including firmware. Example non-transient computer readable storage media includes random access memory (RAM), read only memory (ROM), flash memory, hard disk storage, electronically erasable and programmable ROM (EEPROM), electronically programmable ROM (EPROM), magnetic disk storage, and any other medium which can be used to carry or store processing instructions and data structures and which can be accessed by a general purpose or special purpose computer or other processing device.

Certain operations of controller26described herein include operations to interpret and/or to determine one or more parameters. Interpreting or determining, as utilized herein, includes receiving values by any method known in the art, including from a datalink, network communication or input device, receiving an electronic signal (e.g. a voltage, frequency, current, or pulse-width-modulation signal) indicative of the value, such as the SOC of energy storage system22, receiving a computer generated parameter indicative of the value, reading the value from a memory location on a non-transient machine readable storage medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted parameter can be calculated, and/or by referencing a default value that is interpreted to be the parameter value.

The term “logic” as used herein includes software and/or firmware executing on one or more programmable processors, application-specific integrated circuits, field-programmable gate arrays, digital signal processors, hardwired logic, or combinations thereof. Therefore, in accordance with the embodiments, various logic may be implemented in any appropriate fashion and would remain in accordance with the embodiments herein disclosed.

Returning toFIG.1, in operation engine14may generate power in a known manner which is transferred through clutch16and MG18to drive operation of transmission20. Transmission20may be shifted into different gears (not shown) to increase or decrease the speed of operation of final drive24, and therefore the rotation of wheels34via drive shaft32. In a known manner, MG18may supply power to transmission20in addition to or instead of engine14to cause rotation of wheels34in the manner described above.

In the depicted embodiment, vehicle10includes a start/stop feature implemented by controller26to control operation of engine14. More specifically, when power is not needed from engine14to propel vehicle10, such as when vehicle10is stopped or coasting down an incline, controller26may cause engine14to stop, thereby conserving fuel and reducing emissions. Typically, when engine14is stopped in this manner, engine14coasts from its current speed to a reduced speed or zero speed as a result of friction. When an engine controller or an operator indicates that torque will be required from engine14, such as by depressing the accelerator or releasing the brake pedal, engine14is restarted using one of a variety of known restart mechanisms. According to the principles of the present disclosure, engine14is slowed during shutdown using MG18to recovery kinetic energy in the manner described below.

Referring now toFIG.2, an exemplary process40according to the present disclosure is shown. At step42, controller26initiates an engine stop command such as by processor28determining from various sensors that power from engine14is not required. As indicated above, this may occur under various circumstances such as when the speed of vehicle10is zero or near zero (e.g., at a stop light) or when the torque required from engine14is zero or near zero (e.g., when vehicle10is coasting down an incline). Regardless of the cause for the engine stop command, controller26sends one or more control signals to engine14and/or components associated with engine14to terminate engine operation. For example, the fuel injection system (not shown) associated with engine14may be caused to cease injecting fuel into the engine cylinders.

When engine14operation, is terminated at step42, engine14will “coast” briefly to a zero or near zero torque condition. In step44of process40, controller26monitors engine14and MG18(which may also be in motion just before the engine stop command) as engine14and MG18are allowed to reduce their respective torque outputs to zero or near zero. When both engine14and MG18are in a zero or near zero torque condition, controller26commands transmission20to shift to a neutral gear. This decouples MG18from final drive24to permit MG18to be used for energy recovery from engine14as described below without directly affecting the speed of vehicle10. At this point in process40, engine14may still be slowing to a zero or near zero speed. In other words, the internally moving components of engine14(e.g., the pistons, crankshaft, etc.) will continue to move for some period of time and, if the stop condition is sufficiently long, will come to a stop as a result of friction and other forces.

After transmission20is shifted to neutral (step46), at step48MG18is used in a generator mode to load engine14and recover the engine's kinetic energy. This additional load on engine14causes engine14to reach a zero or near-zero speed condition more quickly than if engine14were simply allowed to coast to a stop. The energy recovered by MG18from engine14is provided to energy storage system22and stored for future use.

At step50of process40, after engine14and MG18have slowed to a zero speed or near zero speed condition, controller26causes clutch16to open. This decouples engine14and MG18and permits MG18to reengage transmission20. Once decoupled from engine14at step50, MG18is commanded at step52by controller26to accelerate back up to the target speed, which is the speed corresponding to that needed for transmission20to shift back into gear. At step54, controller26causes transmission20to shift back into gear. It should be understood that the gear into which transmission20shifts at step54need, not be the same gear out of which transmission20shifted in step46. After this, MG18is used to propel vehicle10in an all-electric mode as indicated by step56. MG18will continue to be used to propel vehicle10until additional torque is required from engine14to meet the operator's demands. When additional torque is required, controller26causes engine14to be restarted in any of a variety of ways known to those skilled in the art.

Referring now toFIG.3, simulation results60are shown using the principles outlined above. The results were generated on a simulation of a powertrain with a diesel engine and a MG capable of absorbing approximately 700 nm of torque from the engine as the engine slows to a zero speed condition as described above. Prior to shutdown, the engine contained a total of 30.17 kJ of kinetic energy in this example. As shown, through use of the methodology described herein approximately 67% of the kinetic energy of the engine was recovered (see “recovered energy” section62). The simulation indicated that approximately 21% of the engine's initial kinetic energy was lost due to engine pumping and friction (section64) and approximately 12% of the kinetic energy was lost due to inefficiencies associated with the MG (section66).

Referring now toFIG.4, an alternative configuration hybrid vehicle10A is shown including a powertrain12A having an internal combustion engine14A, a clutch16A, a MG18A, and a second clutch19. In this embodiment, the transmission20is optional. Like vehicle10ofFIG.1, vehicle10A further includes an energy storage system22A, a final drive24A and a controller26A, including a processor28A and a memory30A. Powertrain12A may include other components and is only depicted as shown to describe the operation of the technology of the present disclosure. For example, the powertrain may include additional MGs18. Moreover, vehicle10A may be configured as a mild hybrid, a full hybrid or a plug-in hybrid. Additionally, while the description herein contemplates use of powertrain12A, the teachings of the present disclosure may be used in other applications such as in a hydraulic hybrid powertrain. Finally, the teachings of the present disclosure may have application to powertrains for equipment other than vehicles.

Referring now toFIG.5, an exemplary process40A according to the present disclosure is shown. At step42A, controller26A initiates an engine stop command such as by processor28A determining from various sensors that power from engine14A is not required. As indicated above, this may occur under various circumstances such as when the speed of vehicle10A is zero or near zero (e.g., at a stop light) or when the torque required from engine14A is zero or near zero (e.g., when vehicle10A is coasting down an incline). Regardless of the cause for the engine stop command, controller26A sends one or more control signals to engine14A and/or components associated with engine14A to terminate engine operation. For example, the fuel injection system (not shown) associated with engine14A may be caused to cease injecting fuel into the engine cylinders.

When engine14A operation is terminated at step42A, engine14A will “coast” briefly to a zero or near zero torque condition. In step44A of process40A, controller26A monitors engine14A and MG18A (which may also be in motion just before the engine stop command) as engine14A and MG18A are allowed to reduce their respective torque outputs to zero or near zero. When both engine14A and MG18A are in a zero or near zero torque condition, controller26opens second clutch19. This decouples MG18A from final drive24A to permit MG18A to be used for energy recovery from engine14A as described below without directly affecting the speed of vehicle10A. At this point in process40A, engine14A may still be slowing to a zero or near zero speed. In other words, the internally moving components of engine14A (e.g., the pistons, crankshaft, etc.) will continue to move for some period of time and, if the stop condition is sufficiently long, will come to a stop as a result of friction and other forces.

After second clutch19is opened (step46), at step48A, MG18A is used in a generator mode to load engine14A and recover the engine's kinetic energy. This additional load on engine14A causes engine14A to reach a zero or near-zero speed condition more quickly than if engine14A were simply allowed to coast to a stop. The energy recovered by MG18A from engine14A is provided to energy storage system22A and stored for future use.

At step50A of process40A, after engine14A and MG18A have slowed to a zero speed or near zero speed condition, controller26A causes clutch16A to open. This decouples engine14A and MG18A and permits MG18A to reengage transmission20A. Once decoupled from engine14A at step50A, MG18A is commanded at step52A by controller26A to accelerate back up to the target speed. At step54, controller26causes second clutch19to close. After this, MG18A is used to propel vehicle10A in an all-electric mode as indicated by step56A. MG18A will continue to be used to propel vehicle10A until additional torque is required from engine14A to meet the operator's demands. When additional torque is required, controller26A causes engine14A to be restarted in any of a variety of ways known to those skilled in the art.

As may be apparent from the foregoing, the benefits of the methodology described herein may be dependent in part upon the torque capability of MG18for at least two reasons. First, since a larger MG18accomplishes step48more quickly (i.e., brings the engine speed to zero or near zero more quickly), less energy is lost to engine pumping and friction. Second, also as a result of step48being performed more quickly, a larger MG18permits the entire process of shutting the engine down and enabling the MG to power the vehicle can be accomplished more quickly. This reduces the torque interrupt time associated with an engine shutdown and results in less impact on vehicle drivability.

Additionally, it should be understood that by reducing the energy lost during engine shutdowns, the present methodology reduces the penalty associated with engine start/stop systems. Consequently, controller26may initiate engine shutdowns more frequently thereby improving energy efficiency and decreasing emissions.

While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications.

In the detailed description herein, references to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art with the benefit of the present disclosure to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.