Patent Application
20150175149
The present disclosure relates to vehicles with an engine auto-stop feature and controlling engine idle stop and restart activities.
A hybrid vehicle may be equipped with an engine auto-stop system. An engine auto-stop system shuts down the engine during certain periods of vehicle operation to conserve fuel. For example, engine auto-stop may be engaged when the vehicle is stopped at a traffic light or in a traffic jam rather than permitting the engine to idle. The engine may be restarted when the driver releases the brake or actuates the accelerator pedal. The engine may also be started, for example, due to loads on the electrical system. Stopping the engine when it is not needed improves fuel economy and reduces emissions.
Engine auto-stop systems may also pose various challenges. An engine stop and restart event causes extra electrical load to be imposed on the system. For example, additional electrical energy is required to restart the engine, to run an electric pump to keep line pressure and reduce engine restart time, and to run an auxiliary heater core pump to maintain cabin comfort. However, during engine stop, there are electrical energy savings as well because some components that are related to engine operations are turned off. These may include the engine cooling fan, air conditioning clutch, fuel pump, fuel injector, and a spark plug coil, for example. Accordingly, there is a need to develop engine auto-stop control strategies that balance the extra electrical load imposed on the vehicle with electrical energy saved during engine stop and restart to achieve net fuel savings.
A system and method for controlling engine idle stop in a hybrid vehicle that balances the extra electrical load imposed on the vehicle during engine stop with the electrical energy saved to achieve net fuel savings is disclosed. Specifically, embodiments disclosed herein use predictive information to generate a predicted vehicle stop profile that depicts potential stop events, along with corresponding vehicle stop duration times, over a specified period of time. A controller may be configured to determine whether a predicted vehicle stop duration time for a vehicle stop event is sufficient to yield net fuel savings. If the predicted stop duration time is long enough to yield net fuel savings, the engine is shut down. If not, engine stop is inhibited.
In one embodiment, a hybrid vehicle includes an engine and a starter motor configured to start the engine. The vehicle also includes a controller configured to inhibit engine stop during a vehicle stop event in response to a predicted vehicle stop duration time being below a minimum engine stop time. The minimum engine stop time is based on electrical load of components started in response to the engine stop and electrical load of the starter motor to restart the engine. The controller is also configured to shut the engine off during the vehicle stop event in response to the predicted vehicle stop duration time exceeding the minimum engine stop time. The minimum engine stop time is further based on a difference between a total added electrical load associated with components that are turned on and a total saved electrical load associated with the components that are turned off during engine stop and restart.
In another embodiment, a hybrid vehicle includes a controller configured to shut the engine off during a vehicle stop event in response to a predicted vehicle stop time exceeding a corresponding engine stop threshold based on vehicle energy consumption with the engine on relative to vehicle energy consumption with the engine off during the vehicle stop event. In addition, the vehicle energy consumption associated with components turned on and off during the vehicle stop event is estimated from current draw of the component, vehicle system voltage, and duration of on and off time of the component. The engine stop threshold is further based on at least one of a fuel consumption rate at engine idle, a fuel energy density, an engine efficiency, and an alternator efficiency.
In yet another embodiment, a method for controlling a hybrid vehicle includes controlling engine stop during a vehicle stop event in response to a comparison of a predicted vehicle stop duration relative to a minimum engine stop time. The minimum engine stop time is based on vehicle energy consumption with the engine running relative to vehicle energy consumption with the engine off during the engine stop and restart.
Embodiments according to the present disclosure provide various advantages. For example, various embodiments achieve net fuel savings by balancing electrical energy added to the system with electrical energy savings during engine stop and restart. The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.
As required, detailed embodiments of the claimed subject matter are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ embodiments of the claimed subject matter.
A hybrid vehicle may be equipped with an engine auto-stop system. An engine auto-stop system shuts down the engine during certain periods of vehicle operation to conserve fuel. For example, the auto-stop system may shut the engine off during engine idle conditions where the engine is not required for propulsion or other purposes. The auto-stop system may then restart the engine when required for propulsion or other purposes. By disabling the engine when possible, overall fuel consumption is reduced. However, unlike true hybrid vehicles, vehicles with an auto-stop feature are not capable of pure electric propulsion and are not equipped with a traction battery, but rather with a conventional starting, lighting, and ignition (SLI) battery.
Referring to
Controller 110 may be configured to initiate an auto-stop or auto-start of the engine 112 during various operating conditions. As the vehicle comes to a stop, for example, controller 110 may issue a command to begin the process to stop the engine 112, thus preventing the alternator or integrated starter generator from providing electric current to the electrical loads. The battery may provide electric current to the electrical loads while the engine is stopped. As the brake pedal is disengaged (and/or the accelerator pedal is engaged) after an engine auto-stop, the controller may issue a command to begin the process to start the engine, thus enabling the alternator or integrated starter generator to provide electric current to the electrical loads.
In general, controller 110 receives input from various vehicle sensors 148 that indicate engine, transmission, electrical and climate states 128. The vehicle speed 132 is also communicated to controller 110 through speed sensor 144. The controller 110 further receives input from driver controls 130, such as the accelerator and brake pedals 146, and a navigation system 136 that provides information to predict and determine durations of upcoming vehicle stop events 134. The navigation system 136 may receive information from the vehicle speed sensor 144, GPS 142, local gradient maps and sensors 140, and/or traffic flow data 138. In one configuration, the navigation system 136 may be an in-vehicle GPS system. In another configuration, the navigation system 136 may comprise a location-enabled mobile device, such as a cellular phone or standalone GPS unit. Other configurations are, of course, also possible. The controller 110 may generally implement engine stop and start, with one or more of the additional features provided by embodiments of the disclosure as described in further detail below.
With continual reference to
As previously discussed, implementing engine auto-stop control strategies may pose various challenges. Engine stop and restart events cause extra electrical load to be imposed on the system. For example, additional electrical energy is required to restart the engine, to run an electric pump to keep line pressure and reduce engine restart time, and to run an auxiliary heater core pump to maintain cabin comfort. However, during engine stop, there are electrical energy savings as well because some components that are related to engine operations are turned off. These may include, the engine cooling fan, air conditioning clutch, and fuel pump, a fuel injector, and a spark plug coil, for example. The net fuel saving is offset by the above extra electrical load and electrical energy savings.
Engine idle stop in a hybrid vehicle can be controlled, based on vehicle energy consumption, to balance the extra electrical load imposed on the vehicle during engine stop with the electrical energy saved to achieve net fuel savings through the use of predictive information. Specifically, embodiments disclosed herein use predictive information to generate a predicted vehicle stop profile that depicts potential vehicle stop events, along with corresponding vehicle stop duration times, over a specified period of time. A controller may then be configured to determine whether the predicted vehicle stop duration time is sufficient to yield net fuel savings. If the predicted vehicle stop duration time is long enough to yield net fuel savings, the controller may command the engine to shut down. If not, the controller may inhibit engine stop.
The predictability of vehicle stop duration times has improved due to the development and deployment of technologies such as Global Positioning Systems (GPS), Geographic Information Systems (GIS), Vehicle-to-Vehicle (V2V) Communications, Vehicle-to-Infrastructure (V2I) Communications, and traffic flow monitoring systems. Once an intended route is available, a predicted vehicle stop profile can be constructed based on map data, road attributes, real-time and historic traffic information, and/or past driving history of the driver.
During each vehicle stop event, the change in electrical load between the electrical energy added to the system from components turned on during engine stop/start and electrical energy saved from components turned off can be estimated as shown in Equation (1). In Equation 1, Eadded is the total electric load associated with the components that need to be turned on during engine stop and restart, and Esaved is the total electric load associated with the components that are turned off during engine stop. The powertrain related loads considered are expressed in Equations (1a) and (1b).
ΔEload=Eadded−Esaved (1)
E
added
=E
start motor
+E
trans aux pump
+E
aux heater core pump (1a)
E
saved
=E
cooling fan
+E
ACclutch
+E
fuel pump
+E
Fuel Injector
+E
Spark Plug Coils
+ELSE (1b)
The electrical load that is added or saved by each component can be estimated based on the integration of its current draw multiplied by the vehicle system voltage along the duration of the component on or off time. The above equations can also be extended to include non-powertrain related electrical loads such as blowers, heated seats, heated steering wheel, electronic power assisted steering (EPAS), rear defrost, and/or side mirror heat, for example. Depending on the driving conditions, the components included in the non-powertrain related load may be different.
To achieve net fuel savings, the engine stop duration time must be long enough to cover the change in electrical load ΔEload. The minimum engine stop duration time in which the change in electrical load can just be compensated by the fuel saving can be calculated as shown in Equation (2). In Equation (2), {dot over (m)} is the fuel consumption rate at engine idle, p is the fuel energy density, ηeng is the engine efficiency, and ηalt is the alternator efficiency.
Engine stop is permitted only when the predicted vehicle stop duration time (Tsd) of the vehicle stop event exceeds the estimated minimum engine stop time, as shown in Equation (3).
T
sd
>T
min,stop (3)
Referring to
As shown in
As can be seen by the representative embodiments described, embodiments according to the present disclosure help mitigate the challenges posed by stop/start vehicles and achieve net fuel savings by balancing the extra electrical load imposed on the vehicle with electrical energy saved during engine stop and restart.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure. While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments discussed herein that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
