US-12617387-B2 - Method and system for improving fuel economy of a hybrid powertrain in a vehicle

Abstract

Methods and systems for improving fuel economy and reducing emissions of a vehicle with an electric motor, an engine and an energy storage device are disclosed. The methods and systems involve obtaining lookahead information and current state information, wherein the lookahead information includes a predicted vehicle speed, and the current state information includes a current state of charge (SOC) for the energy storage device coupled to the electric motor; and determining, based on the lookahead information and the current state information, a target power split between the energy storage device and the engine.

Inventors

• Archit N. Koti
• Rohinish Gupta
• Xing Jin
• Kenneth M. Follen
• Arun Prakash Thunga Gopal
• Manik Narula

Assignees

• CUMMINS INC.

Dates

Publication Date

20260505

Application Date

20240410

Claims (18)

1. 1 . A method of improving fuel economy and reducing emissions of a vehicle with an electric motor, an engine, and an energy storage device coupled to the electric motor, the method comprising: obtaining, by a system control unit, lookahead information and current state information, wherein the lookahead information includes a predicted catalyst temperature, and the current state information includes a current catalyst temperature and a current state of charge (SOC) for the energy storage device; determining, by the system control unit based on the lookahead information and the current state information, a target power split between the energy storage device and the engine; and controlling, by the system control unit based on the predicted catalyst temperature and a difference between the current SOC and the target SOC, a load applied to the engine for the energy storage device to meet a power level defined by the target power split.
2. 2 . The method of claim 1 , wherein determining the target power split comprises: determining, by the system control unit, a high catalyst temperature threshold and a low catalyst temperature threshold.
3. 3 . The method of claim 2 , wherein determining the target power split comprises: determining, by the system control unit, that the predicted catalyst temperature is below the low catalyst temperature threshold; and modifying, by the system control unit, the target power split such that the engine operates at a dynamically determined first optimum point to increase the current catalyst temperature.
4. 4 . The method of claim 2 , wherein determining the target power split comprises: determining, by the system control unit, that the predicted catalyst temperature is above the high catalyst temperature threshold; and modifying, by the system control unit, the target power split such that the engine operates at a dynamically determined second optimum point to decrease the current catalyst temperature.
5. 5 . The method of claim 2 , wherein determining the target power split comprises: determining, by the system control unit, that the predicted catalyst temperature is above the low catalyst temperature threshold and below the high catalyst temperature threshold; and modifying, by the system control unit, the target power split such that the engine operates at a dynamically determined third optimum point to maintain the current catalyst temperature.
6. 6 . The method of claim 1 , wherein the current state information further includes a vehicle power capability comprising at least one of an engine power capability, a motor power capability, and an energy storage device power capability.
7. 7 . A method of improving fuel economy and reducing emissions of a vehicle with an electric motor, an engine and an energy storage device, the method comprising: determining, by a system control unit, that the vehicle is stopped; obtaining, by the system control unit, lookahead information and current state information, wherein the lookahead information includes a predicted stop time, a predicted power demand, and a predicted catalyst temperature and the current state information includes a current catalyst temperature, a catalyst response time, and a current engine state; determining, by the system control unit based on the lookahead information and the current state information, a target engine state and a target engine load; and controlling, by the system control unit, the engine to meet the target engine state and the target engine load.
8. 8 . The method of claim 7 , wherein the target engine state is an engine state when the engine is maintained in an off-state until the engine is turned on at a target engine start time.
9. 9 . The method of claim 8 , wherein determining the target engine state and the target engine load further comprises: determining, by the system control unit, that the predicted stop time is longer than the catalyst response time; and dynamically calculating, by the system control unit, the target engine start time based on at least the catalyst response time and the predicted stop time.
10. 10 . A vehicle system comprising: an engine; an electric motor; an energy storage device coupled with the electric motor; and a controller configured to: obtain lookahead information and current state information, wherein the lookahead information includes a predicted catalyst temperature, and the current state information includes a current catalyst temperature and a current SOC for the energy storage device; determine, based on the lookahead information and the current state information, a target power split between the energy storage device and the engine; and control, based on the predicted catalyst temperature and a difference between the current SOC and the target SOC, a load applied to the engine for the energy storage device to meet a power level defined by the target power split.
11. 11 . The vehicle system of claim 10 , wherein the controller determines the target power split by determining a high catalyst temperature threshold and a low catalyst temperature threshold.
12. 12 . The vehicle system of claim 11 , wherein the controller determines the target power split by: determining that the predicted catalyst temperature is below the low catalyst temperature threshold; and modifying the target power split such that the engine operates at a dynamically determined first optimum point to increase the current catalyst temperature.
13. 13 . The vehicle system of claim 11 , wherein the controller determines the target power split by: determining that the predicted catalyst temperature is above the high catalyst temperature threshold; and modifying the target power split such that the engine operates at a dynamically determined second optimum point to decrease the current catalyst temperature.
14. 14 . The vehicle system of claim 11 , wherein the controller determines the target power split by: determining that the predicted catalyst temperature is above the low catalyst temperature threshold and below the high catalyst temperature threshold; and modifying the target power split such that the engine operates at a dynamically determined third optimum point to maintain the current catalyst temperature.
15. 15 . The vehicle system of claim 10 , wherein the current state information further includes a vehicle power capability comprising at least one of an engine power capability, a motor power capability, and an energy storage device power capability.
16. 16 . A vehicle system comprising: an engine; an electric motor; an energy storage device coupled with the electric motor; and a controller configured to: determine that the vehicle system is stopped; obtain lookahead information and current state information, wherein the lookahead information includes a predicted stop time, a predicted power demand, and a predicted catalyst temperature and the current state information includes a current catalyst temperature, a catalyst response time, and a current engine state; determine, based on the lookahead information and the current state information, a target engine state and a target engine load; and control the engine to meet the target engine state and the target engine load.
17. 17 . The vehicle system of claim 16 , wherein the target engine state is an engine state when the engine is maintained in an off-state until the engine is turned on at a target engine start time.
18. 18 . The vehicle system of claim 17 , wherein the controller determines the target engine state and the target engine load by: determining that the predicted stop time is longer than the catalyst response time; and dynamically calculating the target engine start time based on at least the catalyst response time and the predicted stop time.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisional of and claims the benefit and priority of U.S. Ser. No. 17/611,082, filed on Nov. 12, 2021, which claims priority to and is a U.S. national stage of International Application No. PCT/US2020/032651, filed on May 13, 2020, which claims priority to U.S. Provisional Application No. 62/846,993, filed on May 13, 2019, the entire contents of which are incorporated herein by reference in their entirety. GOVERNMENT SUPPORT CLAUSE This material is based upon work supported by the Department of Energy under Award Number(s) DE-EE0007761. The Government has certain rights in this invention. FIELD OF THE DISCLOSURE The present disclosure relates generally to hybrid vehicles, especially to improving fuel economy of the hybrid vehicles. BACKGROUND OF THE DISCLOSURE Recently, there has been an increased demand for vehicles with hybrid powertrains, i.e. hybrid vehicles with multiple forms of motive power, to meet criteria such as improved fuel economy and reduced emissions, all the while maintaining optimal performance for the user. When a hybrid vehicle is moving at a slow speed with a number of stop-starts (i.e., in heavy traffic), with the transmission in a forward gear, but with the driver not pressing the accelerator pedal, the vehicle slowly moves forward in a state known as creep idling. It is preferable to avoid this type of engine idling because much of the fuel that is used during this time is wasted, when it would be more efficient to use the same amount of fuel in a road with light traffic to allow the vehicle to be driven at a much faster speed. Also, when the temperature of a catalyst used in a selective catalytic reduction (SCR) system is too low or too high, the efficiency of the SCR system drops considerably, causing more nitrogen oxides (NOx) to be released into the atmosphere as vehicle emissions before they can be reduced into diatomic nitrogen and water with the help of a catalyst, such as ammonia. Therefore, it is preferable to avoid using the engine and instead use the electric motor, if possible, to drive the hybrid vehicle when the catalyst temperature is too low and when the catalyst temperature is too high. Furthermore, turning on the engine while the hybrid vehicle is stopped on the road causes an increase in the NOx emissions from the vehicle. This is because when the engine is initially turned on, the catalyst temperature within the SCR system is not yet high enough to allow for the SCR system to operate efficiently, so the engine needs to keep running for a period of time to raise the catalyst temperature to a preferred temperature. During this process, until the catalyst temperature reaches the preferred temperature, the SCR system continues to operate but not at its optimal efficiency, thereby causing more NOx emissions to be released into the atmosphere. FIG. 1 illustrates the simulated relationship between time and catalyst temperature for a diesel engine at different power operating points. The graph shows such data for a first operating point 100 at 25 kW power, a second operating point 102 at 50 kW power, a third operating point 104 at 75 kW power, a fourth operating point 106 at 100 kW power, a fifth operating point 108 at 125 kW power, a sixth operating point 110 at 150 kW power, and a seventh operating point 112 at 175 kW power. As shown in FIG. 1, an operating point at a higher power is likely to reach the preferred catalyst temperature faster than another operating point at a lower power. In view of the above examples, there is a need to operate the hybrid powertrains in hybrid vehicles such that operation of the electric motor and the engine is controlled in a way that is as efficient as possible in terms of fuel economy and reduced emissions. SUMMARY OF THE DISCLOSURE Various embodiments of the present disclosure relate to methods and systems to improve fuel economy and reduce emissions of a vehicle with an electric motor, an engine and an energy storage device. In one embodiment, the method involves obtaining lookahead information and current state information, wherein the lookahead information includes a predicted vehicle speed, and the current state information includes a current state of charge (SOC) for the energy storage device coupled to the electric motor. The method also involves determining, based on the lookahead information and the current state information, a target power split between the energy storage device and the engine. In one aspect of the embodiment, the target power split is determined by: determining a threshold vehicle speed and an average predicted vehicle speed over a predetermined time period or distance horizon; when the average predicted vehicle speed is below the threshold vehicle speed, modifying the target power split such that the energy storage device on board is charged to a target value based on the lookahead information and the current state information; and when the aver