Patent ID: 12194981

DETAILED DESCRIPTION

The following description relates to systems and methods for operating a vehicle. The vehicle may include an internal combustion engine and/or an electric machine to provide propulsive force to the vehicle. The vehicle powertrain may be of the type that is shown inFIG.1or other known configurations. Wheel torque for the vehicle may be determined according to a relationship between mapped driver demand torque and a driver demand wheel torque request. The mapped driver demand torque may be determined from a position of a driver demand wheel torque input device (e.g., a propulsion pedal, lever, human/machine interface, or an autonomous driver) and vehicle speed. The relationship between a mapped driver demand wheel torque and a driver demand wheel torque request may include a breakpoint that represents a minimum requested wheel torque. The minimum requested wheel torque may be determined from several torque values as shown inFIG.3so that vehicle drivability may meet expectations. A method for determining and generating a minimum wheel torque request is provided inFIG.4.

The mapped driver demand wheel torque may be generated according to propulsion pedal position or a position or state of another device (e.g., a lever or an autonomous driver). The mapped driver demand wheel torque may vary from a minimum wheel torque to a maximum wheel torque. However, it may not be desirable to leave the minimum wheel torque as a single value because a single value may not be suitable for all driving conditions. For example, when a vehicle's driver releases a propulsion pedal and the vehicle is coasting, it may be desirable to generate a minimum wheel torque request that is negative so that the vehicle may be slowed at a desired rate. On the other hand, if the vehicle is stopped and the driver releases the propulsion pedal, it may be desirable to generate a small positive wheel torque. Thus, a single value minimum wheel torque request may not be desirable during all vehicle operating conditions.

The inventors herein have recognized that desirable vehicle drivability may be achieved via a method for operating a vehicle, comprising: selecting a minimum wheel torque from a plurality of torques; including the minimum wheel torque in a relationship between a mapped driver demand wheel torque input and a driver demand wheel torque request; and adjusting torque of a powertrain propulsion source as a function of the relationship between the mapped driver demand wheel torque and the driver demand wheel torque request.

By selecting a minimum wheel torque from a plurality of torques, it may be possible to provide the technical result of improving vehicle drivability when a vehicle's driver releases a propulsion pedal under different driving conditions. In one example, the minimum wheel torque request may be selected from a vehicle coasting drivability torque, a powertrain capability minimum wheel torque, a creep wheel torque, and a smooth transition wheel torque.

The present description may provide several advantages. In particular, the approach may be useful for providing minimum wheel torque values for a variety of different driveline configurations. Further, the approach may improve vehicle drivability. In addition, the approach may improve vehicle operation when the propulsion pedal transitions from an unapplied state to an applied state.

Turning now to the figures,FIG.1illustrates an example vehicle propulsion system100for vehicle121. Vehicle propulsion system100may include at least two propulsion sources including an internal combustion engine110and an electric machine120. However, in some examples, vehicle propulsion system100may include only electric machine120, or alternatively, a plurality of electric machines that operate as vehicle propulsion sources. The methods described herein may apply when vehicle propulsion system100is configured as a hybrid vehicle, electric vehicle, or conventional internal combustion engine based vehicle.

Electric machine120may be configured to utilize or consume a different energy source than engine110. For example, engine110may consume liquid fuel (e.g. gasoline) to produce an engine output while electric machine120may consume electrical energy to produce an electric machine output. As such, a vehicle with propulsion system100may be referred to as a hybrid electric vehicle (HEV). Throughout the description ofFIG.1, mechanical connections between various components is illustrated as solid lines, whereas electrical connections between various components are illustrated as dashed lines.

Vehicle propulsion system100has a front axle (not shown) and a rear axle122. In some examples, rear axle may comprise two half shafts, for example first half shaft122a, and second half shaft122b. Vehicle propulsion system100further has front wheels130and rear wheels131. In this example, front wheels130are not driven and rear wheels131are driven electrically or via engine110. However, in other examples, front wheels130may be driven via an electric machine. The rear axle122is coupled to electric machine120and to transmission125via driveshaft129. The rear axle122may be driven either purely electrically and exclusively via electric machine120(e.g., electric only drive or propulsion mode, engine is not combusting air and fuel or rotating), in a hybrid fashion via electric machine120and engine110(e.g., parallel mode), or exclusively via engine110(e.g., engine only propulsion mode), in a purely combustion engine-operated fashion. Rear drive unit136may transfer power from engine110or electric machine120, to axle122, resulting in rotation of drive wheels131. Rear drive unit136may include a gear set, differential193, and an electrically controlled differential clutch191that adjusts torque transfer to axle122aand to axle122b. In some examples, electrically controlled differential clutch191may communicate a clutch torque capacity (e.g., an amount of torque the clutch may transfer and it may increase in response to an increasing force applied to close the clutch) of the electrically controlled differential clutch via CAN bus299. Torque transfer to axle122aand122bmay be equal when electrically controlled differential clutch is open. Torque transfer to axle122amay be different from torque transferred to axle122bwhen electrically controlled differential clutch191is partially closed (e.g., slipping such that speed input to the clutch is different than speed output of the clutch) or closed. Rear drivel unit136may also include one or more clutches (not shown) to decouple transmission125and electric machine120from wheels131. Rear drive unit136may be directly coupled to electric machine120and axle122. In some examples, a motor positioned directly downstream of transmission125in the direction of positive torque flow from the engine110may be substituted for rear drive unit136.

A transmission125is illustrated inFIG.1as connected between engine110, and electric machine120assigned to rear axle122. In one example, transmission125is an automatic transmission that includes a torque converter128. Transmission125may shift gears by selectively opening first clutch126and closing second clutch127. Transmission125may include a plurality of clutches and gears.

Electric machine120may receive electrical power from onboard electrical energy storage device132. Furthermore, electric machine120may provide a generator function to convert engine output or the vehicle's kinetic energy into electrical energy, where the electrical energy may be stored at electric energy storage device132for later use by the electric machine120or integrated starter/generator142. A first inverter system controller (ISC1)134may convert alternating current generated by electric machine120to direct current for storage at the electric energy storage device132and vice versa. Electric energy storage device132may be a battery, capacitor, inductor, or other electric energy storage device.

In some examples, electric energy storage device132may be configured to store electrical energy that may be supplied to other electrical loads residing on-board the vehicle (other than the motor), including cabin heating and air conditioning, engine starting, headlights, cabin audio and video systems, etc.

Control system14may communicate with one or more of engine110, electric machine120, energy storage device132, integrated starter/generator142, transmission125, etc. Control system14may receive sensory feedback information from one or more of engine110, electric machine120, energy storage device132, integrated starter/generator142, transmission125, etc. Further, control system14may send control signals to one or more of engine110, electric machine120, energy storage device132, transmission125, etc., responsive to this sensory feedback. Control system14may receive an indication of an operator requested output of the vehicle propulsion system from a human operator102, or an autonomous controller. For example, control system14may receive sensory feedback from pedal position sensor194which communicates with pedal192. Pedal192may refer schematically to a propulsion pedal. Similarly, control system14may receive an indication of an operator requested vehicle braking via a human operator102, or an autonomous controller. For example, control system14may receive sensory feedback from pedal position sensor157which communicates with brake pedal156.

Energy storage device132may periodically receive electrical energy from a power source180(e.g., a stationary power grid) residing external to the vehicle (e.g., not part of the vehicle) as indicated by arrow184. As a non-limiting example, vehicle propulsion system100may be configured as a plug-in hybrid electric vehicle (HEV), whereby electrical energy may be supplied to energy storage device132from power source180via an electrical energy transmission cable182. During a recharging operation of energy storage device132from power source180, electrical transmission cable182may electrically couple energy storage device132and power source180. In some examples, power source180may be connected at inlet port150. Furthermore, in some examples, a charge status indicator151may display a charge status of energy storage device132.

In some examples, electrical energy from power source180may be received by charger152. For example, charger152may convert alternating current from power source180to direct current (DC), for storage at energy storage device132. Furthermore, a DC/DC converter153may convert a source of direct current from charger152from one voltage to another voltage. In other words, DC/DC converter153may act as a type of electric power converter.

While the vehicle propulsion system is operated to propel the vehicle, electrical transmission cable182may be disconnected between power source180and energy storage device132. Control system14may identify and/or control the amount of electrical energy stored at the energy storage device, which may be referred to as the state of charge (SOC).

In other examples, electrical transmission cable182may be omitted, where electrical energy may be received wirelessly at energy storage device132from power source180. For example, energy storage device132may receive electrical energy from power source180via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. As such, it should be appreciated that any suitable approach may be used for recharging energy storage device132from a power source that does not comprise part of the vehicle. In this way, electric machine120may propel the vehicle by utilizing an energy source other than the fuel utilized by engine110.

Electric energy storage device132includes an electric energy storage device controller139and a power distribution module138. Electric energy storage device controller139may provide charge balancing between energy storage element (e.g., battery cells) and communication with other vehicle controllers (e.g., controller12). Power distribution module138controls flow of power into and out of electric energy storage device132.

One or more wheel speed sensors (WSS)195may be coupled to one or more wheels of vehicle propulsion system100. The wheel speed sensors may detect rotational speed of each wheel. Such an example of a WSS may include a permanent magnet type of sensor.

Vehicle propulsion system100may further include a starter140. Starter140may comprise an electric motor, hydraulic motor, etc., and may be used to rotate engine110so as to initiate engine110operation under its own power.

Vehicle propulsion system100may further include a brake system control module (BSCM)141. In some examples, BSCM141may comprise an anti-lock braking system, such that wheels (e.g.130,131) may maintain tractive contact with the road surface according to driver inputs while braking, which may thus prevent the wheels from locking up, to prevent skidding. In some examples, BSCM may receive input from wheel speed sensors195.

Vehicle propulsion system100may further include a belt integrated starter/generator (BISG)142. BISG may produce electric power when the engine110is in operation, where the electrical power produced may be used to supply electric devices and/or to charge the onboard storage device132. As indicated inFIG.1, a second inverter system controller (ISC2)143may receive alternating current from BISG142, and may convert alternating current generated by BISG142to direct current for storage at energy storage device132. Integrated starter/generator142may also provide torque to engine110during engine starting or other conditions to supplement engine torque.

In some examples, vehicle propulsion system100may include one or more electric machines135aand135bto propel vehicle121or to provide regenerative braking via front wheels130. Friction brakes196may be applied to slow front wheels130. Third inverter (ISC3)147amay convert alternating current generated by electric machine135ato direct current for storage at the electric energy storage device132or provide alternating current to electric machine135ato propel vehicle121. Likewise, fourth inverter (ISC4)147amay convert alternating current generated by electric machine135bto direct current for storage at the electric energy storage device132or provide alternating current to electric machine135bto propel vehicle121. Electric machines135aand135bmay be collectively referred to as front wheel electric machines.

Vehicle propulsion system100may further include a power distribution box (PDB)144. PDB144may be used for routing electrical power throughout various circuits and accessories in the vehicle's electrical system.

Controller12may comprise a portion of a control system14. In some examples, controller12may be a single controller of the vehicle. Control system14is shown receiving information from a plurality of sensors16(various examples of which are described herein) and sending control signals to a plurality of actuators81(various examples of which are described herein). As one example, sensors16may include tire pressure sensor(s)197, wheel speed sensor(s)195, ambient temperature/humidity sensor198, onboard cameras105, seat load cells107, door sensing technology108, inertial sensors199, etc. In some examples, sensors associated with engine110, transmission125, electric machine120, etc., may communicate information to controller12, regarding various states of engine, transmission, and motor operation.

Vehicle propulsion system100may also include an on-board navigation system17(for example, a Global Positioning System) on dashboard19that an operator of the vehicle may interact with. The navigation system17may include one or more location sensors for assisting in estimating a location (e.g., geographical coordinates) of the vehicle. For example, on-board navigation system17may receive signals from GPS satellites (not shown), and from the signal identify the geographical location of the vehicle. In some examples, the geographical location coordinates may be communicated to controller12.

Dashboard19may further include a display system18configured to display information to the vehicle operator. Display system18may comprise, as a non-limiting example, a touchscreen, or human machine interface (HMI), display which enables the vehicle operator to view graphical information as well as input commands. In some examples, display system18may be connected wirelessly to the internet (not shown) via controller (e.g.12). As such, in some examples, the vehicle operator may communicate via display system18with an internet site or software application (app).

Dashboard19may further include an operator interface15via which the vehicle operator may adjust the operating status of the vehicle. Specifically, the operator interface15may be configured to initiate and/or terminate operation of the vehicle driveline (e.g., engine110, BISG142, DCT125, and electric machine130) based on an operator input. Various examples of the operator ignition interface15may include interfaces that require a physical apparatus, such as an active key, that may be inserted into the operator ignition interface15to start the engine110and turn on the vehicle, or may be removed to shut down the engine110and turn off the vehicle. Other examples may include a passive key that is communicatively coupled to the operator ignition interface15. The passive key may be configured as an electronic key fob or a smart key that does not have to be inserted or removed from the ignition interface15to operate the vehicle engine110. Rather, the passive key may need to be located inside or proximate to the vehicle (e.g., within a threshold distance of the vehicle). Still other examples may additionally or optionally use a start/stop button that is manually pressed by the operator to start or shut down the engine110and turn the vehicle on or off. In other examples, a remote engine start may be initiated remote computing device (not shown), for example a cellular telephone, or smartphone-based system where a user's cellular telephone sends data to a server and the server communicates with the vehicle controller12to start the engine.

Thus, the system ofFIG.1provides for a system for operating a powertrain, comprising: one or more propulsion sources; and a controller including executable instructions stored in non-transitory memory that cause the controller to adjust a torque of the propulsion source in response to a minimum wheel torque request, where the minimum wheel torque request is a greater of a vehicle coasting drivability wheel torque, a powertrain capability minimum wheel torque, a smooth transition wheel torque, and a creep wheel torque. The system includes where the one or more propulsion sources include an internal combustion engine. The system includes where the one or more propulsion sources include an electric machine. The system further comprising additional instructions to determine the creep wheel torque based on a torque converter characteristic. The system includes where the smooth transition wheel torque is based on a past value of the minimum wheel torque request and a controlled calibratable wheel torque change rate. The system includes where the powertrain minimum wheel torque is zero for vehicle speeds less than a vehicle creep speed minus an offset vehicle speed, it is the actual powertrain minimum capability from all propulsion source projected to the wheel for vehicle speed greater than a vehicle creep speed minus an offset vehicle speed. The system includes where the vehicle coasting drivability wheel torque is based on transmission gear ratio, vehicle speed, and selected drive mode.

FIG.2shows an example relationship between a mapped driver demand wheel torque and a driver demand wheel torque request. The mapped driver demand wheel torque may be determined from an input device (e.g., a propulsion pedal, lever, human/machine interface, or an autonomous driver) and vehicle speed. The horizontal axis represents a mapped driver demand wheel torque. The driver demand wheel torque input device is in a base position, or not applied, where the horizontal axis is intersected by vertical line210. The driver demand wheel torque input device is in a fully applied position where the horizontal line is intersected by line216. Thus, the driver demand wheel torque input device is not applied at the left side of the horizontal axis, and the application amount of the driver demand wheel torque input device increases to the right side of plot200. The vertical axis represents the driver demand wheel torque request, and the amount of the driver demand wheel torque request increases in the direction of the vertical axis arrow.

The mapped driver demand wheel torque input to requested driver demand wheel torque relationship is represented by line segments202,204, and206. Line202may be referred to as a lead-in line segment of the mapped driver demand wheel torque input to driver demand wheel torque request relationship because it starts from the base or unapplied driver demand wheel torque input device base position. Line204may be referred to as a middle line segment of the mapped driver demand wheel torque input to driver demand wheel torque request relationship. Line206may be referred to as a lead-out line segment of the mapped driver demand wheel torque input to driver demand wheel requested torque relationship because line segment206ends with the driver demand wheel torque input device being fully applied.

A first breakpoint250defines a first end of lead-in line segment202. Second breakpoint252defines a second end of lead-in line segment202and a first end of middle line segment line segment204. Third breakpoint254defines a second end of middle line segment line segment204and a first end of lead-out line segment206. The other end of lead-out line segment206is defined by fourth breakpoint256. Breakpoint250may be dynamically adjusted with respect to the vertical axis (e.g., the driver demand wheel torque request) in response to vehicle operating conditions as discussed in further detail with respect to method400.

The first breakpoint250is shown at the intersection of vertical line210and horizontal line220. Vertical line210represents the base or not applied position of the mapped driver demand wheel torque input. Vertical line210also represents a beginning or first side of a lead-in region for the mapped driver demand wheel torque input that extends between vertical line210and vertical line212. Horizontal line220represents the minimum wheel torque request (e.g., the wheel torque request may not be less than the value of the minimum wheel torque request). The minimum wheel torque request Tq_whlMinReq may be adjusted in the direction indicated by arrows270according to vehicle operating conditions as discussed in greater detail in the description ofFIG.4.

The second breakpoint252is shown at the intersection of vertical line212and horizontal line222. Vertical line212represents the end of the lead-in region of the mapped driver demand wheel torque input. Vertical line212also represents a beginning of the middle line segment region of the mapped driver demand wheel torque input that extends to vertical line214. Horizontal line222represents the maximum wheel torque request of the lead-in region. The maximum torque for the lead-in region Tq_whlLeadIn may be adjusted in the direction of the arrows271according to vehicle operating conditions as discussed in greater detail in the description ofFIG.4.

The third breakpoint254is shown at the intersection of vertical line214and horizontal line224. Vertical line214represents the end of the middle line segment region of the mapped driver demand wheel torque input. Vertical line214also represents a beginning of the lead-out region of the mapped driver demand wheel torque input that extends to vertical line216. Horizontal line224represents the maximum wheel torque request of the middle line segment region and the minimum wheel torque of the lead-out region.

The fourth breakpoint256is shown at the intersection of vertical line216and horizontal line226. Vertical line216represents the fully applied position of the mapped driver demand wheel torque input. Vertical line216also represents the end of the lead-out region for the mapped driver demand wheel torque input. Horizontal line226represents the maximum wheel torque request (e.g., the wheel torque request may not be greater than the value of the maximum wheel torque request).

The lead-in line portion of the relationship between a mapped driver demand wheel torque input and a commanded or requested driver demand wheel torque (e.g., line202) provides a gradual increase in requested driver demand wheel torque for an increase in the application amount of the mapped driver demand wheel torque input. The slope of the line segment202may be increased or decreased in response to vehicle operating conditions so that “dead pedal” feel may be avoided. The slope of line segment202may be changed via adjusting the value of Tq_whlLeadIn or the value of Tq_whlMinReq dynamically as a function of vehicle operating conditions. Tq_whlMapXO represents the mapped driver demand input at fully released position of the driver demand wheel torque input device and Tq_whlMapXLow is the mapped driver demand input at the position of the driver demand wheel torque input device at which the lead-in region stops (e.g., 10% of a fully applied driver demand wheel torque input device). In one example, Tq_whlMapXLow=Tq_whlXRL, or the mapped driver demand input at position of the driver demand wheel torque input device at which the lead-in region stops is equal to the mapped driver demand input at road load of the vehicle (Tq_whlXRL). Thus, the lead-in line portion and the lead-out line portion have lower gains (e.g., rates of change of driver demand torque request as a function of mapped driver demand torque) than the middle line section.

Referring now toFIG.3, plots of torques that contribute to a minimum wheel torque request are shown. The torques trajectories ofFIG.3are shown relative to three phases that are a function of vehicle speed.

The first plot from the top ofFIG.3is a plot of minimum wheel torque request and powertrain capable minimum wheel torque versus vehicle speed. The powertrain capable minimum wheel torque is a minimum powertrain torque that may be commanded and generated at the vehicle's wheels. Line308represents the minimum wheel torque request. Line310represents the powertrain capable minimum wheel torque. Vertical line350represents a creep speed of a vehicle. The creep speed may be a speed of the vehicle on a flat road achieved after the vehicle was stopped and after the brake pedal has been released with no propulsion pedal application when the vehicle reaches an equilibrium point where the road load is balanced by the torque converter's positive torque output for a vehicle with automatic transmission. Shaded area302represents a first phase or a creep phase where vehicle speed is lower than the creep speed and the propulsion pedal is fully released. The creep phase is active when vehicle speed is less than or equal to creep speed at line350. Shaded area304represents a second phase or transition phase between the creep phase and a coasting phase. The transition phase is active when vehicle speed is greater than the creep speed at line350and less than the creep speed at line350plus a first vehicle speed offset value. Shaded area306represents a third phase or coasting phase. The coasting phase is active when vehicle speed is greater than the creep speed at line350plus the first offset vehicle speed.

The second plot from the top ofFIG.3is a plot of minimum wheel torque request and creep wheel torque request versus vehicle speed. The creep wheel torque is a torque that propels the vehicle at a predetermined constant speed (e.g., 9 Kilometers/hour) on a flat road after the vehicle was stopped and the vehicle's brake was released without applying the propulsion pedal. Lines and phases numbered in the second plot with the same numbers as lines and phases numbered in the first plot are indicated with same numbers. For example, line308in second plot from the top ofFIG.3and line308in the first plot from the top ofFIG.3both represent the minimum wheel torque request. Therefore, for the sake of brevity their description is omitted. Line312represents the creep wheel torque request.

The third plot from the top ofFIG.3is a plot of minimum wheel torque request and smooth transition wheel torque versus vehicle speed. The smooth transition wheel torque is a torque that controls the torque transition from creep wheel torque to coasting wheel torque. Lines and phases numbered in the third plot with the same numbers as lines and phases numbered in the first plot are indicated with same numbers. For example, line308in third plot from the top ofFIG.3and line308in the first plot from the top ofFIG.3both represent the minimum wheel torque request. Therefore, for the sake of brevity their description is omitted. Line314represents the smooth transition wheel torque.

The fourth plot from the top ofFIG.3is a plot of minimum wheel torque request and vehicle coasting drivability wheel torque versus vehicle speed. The vehicle coasting drivability wheel torque is a torque that controls vehicle deceleration when the vehicle is coasting. Lines and phases numbered in the fourth plot with the same numbers as lines and phases are numbered in the first plot are indicated with same numbers. For example, line308in fourth plot from the top ofFIG.3and line308in the first plot from the top ofFIG.3both represent the minimum wheel torque request. Therefore, for the sake of brevity their description is omitted. Line316represents the vehicle coasting drivability wheel torque.

In the first phase302, vehicle speed is less than or equal to the vehicle creep speed. During the first phase, the creep wheel torque request as shown in the second plot from the top ofFIG.3is greater than the powertrain capable minimum wheel torque310, the smooth transition wheel torque312, and the vehicle coasting wheel torque316. The powertrain capable minimum wheel torque may be adjusted to a value of zero to ensure that the creep wheel torque request is the greater of the torques.

In the second phase304, vehicle speed is greater than vehicle creep speed and less than vehicle creep speed plus an offset vehicle speed. During the second phase, the smooth transition wheel torque as shown in the third plot from the top ofFIG.3is greater than the powertrain capable minimum wheel torque310, the creep wheel torque request312, and the vehicle coasting wheel torque316. The second or transition phase bridges differences between the creep wheel torque request312and the vehicle coasting drivability wheel torque316. The smooth transition wheel torque is one of the dominant torques when the vehicle's propulsion pedal is applied from a fully released position. When the propulsion pedal is applied, the smooth transition torque is a reference torque for the lead-in region to generate the vertical axis ofFIG.2from the horizontal axis. In addition, the smooth transition wheel torque is the dominant torque when vehicle operation transits from coasting to vehicle creep.

In the third phase306, vehicle speed is greater than the vehicle creep speed plus the offset vehicle speed. During the third phase, the vehicle coasting drivability wheel torque as shown in the fourth plot from the top ofFIG.3is greater than the powertrain capable minimum wheel torque310, the smooth transition wheel torque314, and the vehicle creep torque312. The vehicle coasting drivability wheel torque is the dominant torque when the vehicle is coasting.

The vehicle coasting drivability wheel torque, powertrain capable minimum torque, creep wheel torque, and smooth transition wheel torque may be calibrated to provide the torque trajectories in the phases shown inFIG.3. In other words, the parameters that are mentioned in the description ofFIG.4may adjusted to provide the torque trajectories shown inFIG.3.

It may be observed that the minimum wheel torque request follows the creep wheel torque request312in the first phase. Further, the minimum wheel torque request follows the smooth transition torque314in the second phase. The minimum wheel torque request also follows the vehicle coasting drivability wheel torque during the third phase if it is not constrained by the powertrain capable minimum wheel torque.

Referring now toFIG.4, a method for determining a minimum wheel torque request is shown. The method ofFIG.4may be included in the system ofFIG.1as executable instructions stored in non-transitory memory. The method ofFIG.4may operate in cooperation with the system ofFIG.1to adjust operating states of devices (e.g., torque actuators) in the physical world.

At402, method400determines vehicle coasting drivability wheel torque. The vehicle coasting drivability wheel torque is a wheel torque that causes vehicle speed to be reduced at a desired rate that conforms to customer metrics. The rate of vehicle speed reduction may be different for each vehicle drive mode. The vehicle coasting drivability wheel torque may be described via the following equations;
VSRDrvLimit=ƒ(vspd,rttqTransm,SDM)
TqwhlCoastDrv=(VSRDrvLimit·Masseff+Fdrag)·Rtire
where VSRDrvLimitis a vehicle speed reduction limit that is not to be exceeded and desired to have during vehicle coasting, f is a function that returns the vehicle speed reduction limit, vspd is vehicle speed, rttqTransmis the vehicle's transmission torque ratio, and SDM is the vehicle's selected drive mode (e.g., economy, performance, etc.), TqwhlCoastDrvis the vehicle coasting drivability wheel torque, Masseffis the mass of the vehicle, Fdragis the vehicle's drag force, and Rtireis the vehicle's tire radius.

The function f in the vehicle speed reduction limit may be realized via tables holding adjustable values. For vehicles that include an electric machine propulsion source, the vehicle speed reduction limit may be adjusted to provide larger amounts of powertrain braking torque than an internal combustion engine.

The vehicle coasting drivability wheel torque may be provided via several different actuators depending on the vehicle configuration. For example, the deceleration torque may be generated via an engine and engine torque may be adjusted via a throttle, spark retard, fuel injector, and intake and exhaust poppet valve timing. For vehicles that include an electric machine propulsion source, the electric machine may be commanded to provide the vehicle coasting drivability wheel torque. Method400proceeds to404.

At404, method400determines the powertrain minimum wheel torque. The powertrain minimum wheel torque is a smallest value powertrain torque that may be commanded. In one example, the powertrain minimum wheel torque may be expressed via the following equation:

TqwhlPwrtrnMin={0,vspd<vspdcreep-calTqwhlEngFric+TqwhlMtrMin,vspd≥vspdcreep-cal}
where TqwhlPwrtmMinis the powertrain capable minimum wheel torque, vspd is vehicle speed, vspdcreepis the vehicle creep speed, cal is an vehicle speed offset amount, TqwhlEngFricis engine friction torque, TqwhlMtrMinis a minimum torque that may be provided via all electric machine powertrain propulsion sources (e.g., an electric machine that may provide propulsion force for a powertrain and there could be more than one electric machine equipped on the vehicle). Thus, the powertrain capable minimum wheel torque is zero when vehicle speed is less than vehicle creep speed minus an offset vehicle speed. The powertrain capable minimum wheel torque is the engine friction torque plus the minimum torque that may be provided via the electric machine powertrain propulsion source for vehicle speeds greater than or equal to vehicle creep speed minus the offset vehicle speed. The engine friction torque may be zero for electric vehicles and the minimum torque that may be provided by an electric machine propulsion source may be zero for powertrains that do not include an electric machine. Method400proceeds to406.

At406, method400determines the creep wheel torque request. In one example, method400may determine the creep wheel torque request via the following equations:

TqwhlCreepReq=Tqtur·rtgb·rtfdTqtur=f⁡(NidledesNtcreep)·(Nidledes)2/K2(NidledesNtcreep)Ntcreep=vspdcreep·rtgb·rtfd
where TqwhlCreepReqis the wheel torque creep request, Tqturis torque converter turbine torque, rtgbis the transmission gear ratio, rtfdis the final drive or axle gear ratio, K is a torque converter capacity factor that is a function of a speed ratio

Ni⁢d⁢l⁢e⁢d⁢e⁢sNtc⁢r⁢e⁢e⁢p,
Nidledesis the desired engine idle speed, and Ntcreepis the torque converter turbine creep speed. For vehicles without a torque converter, e.g., an electric vehicle, the creep wheel torque request profile can be generated via different calculations (e.g., vehicle speed based calibration table) that once the torque request is provided by the powertrain, driver expected vehicle creep behavior can be met.

The wheel creep torque may be provided via the powertrain electric machine propulsion source, an engine, or a combination of the powertrain electric machine propulsion source and the engine. During vehicle conditions when a driver releases the brake pedal from vehicle stop, the vehicle does not reach creep speed immediately. However, the instantaneous or present vehicle speed may be used as the vehicle's creep speed to determine the wheel torque request. During conditions when a driver applies a propulsion pedal while the vehicle is at or below creep speed, then the wheel creep torque may be adjusted to a value that is less than the vehicle coasting drivability wheel torque. Method400proceeds to408.

At408, method400determines the smooth transition wheel torque. The smooth transition wheel torque may be determined via the following equations:

TqwhlSmTrans={TqwhlMinReqLast+dTqwhlRampdt·TimetipIn(following⁢tip-in)TqwhlCreepReq(during⁢creep)
where TqwhlSmTransis the smooth transition wheel torque, TqwhlMinReqLastis a minimum wheel torque request value immediately preceding a most recent application of a propulsion pedal (e.g., a tip-in) while the vehicle is moving at or below creep speed, dTqwhlRamp/dt is an predetermined calibratable change rate of wheel torque and it is negative to control the ramp down rate of TqwhlSmTrans, TimetipInis the time duration after a tip-in event, TqwhlCreepReqis a wheel creep torque as calculated at406. Thus, following a tip-in, the smooth transition wheel torque may be set to the minimum wheel torque request immediately preceding a most recent application of a propulsion pedal and may reduce with a controlled torque change rate. TqwhlSmTransmay be clipped by TqwhlPwrtrnMinwhen it drops to that negative level. However, while the vehicle is moving at or under creep speed, the smooth transition wheel torque may be set to the wheel creep torque request. Method400proceeds to410.

At410, method400determines the minimum wheel torque value. In one example, method400may determine the minimum wheel torque via the following equation:
TqwhlMinReq=max(TqwhlCoastDrv,TqwhlPwrtrnMin,TqwhlCreepReq,TqwhlSmTrans)
where TqwhlMinReqis the minimum wheel torque request, max is a function that returns the greater of arguments input into the function, TqwhlCoastDrvis the vehicle coasting drivability wheel torque, TqwhlCreepReqis the in wheel creep torque request, TqwhlPwrtrnMinis the powertrain capable minimum wheel torque, and TqwhlSmTransis the smoot transition wheel torque. Method400proceeds to412.

At412, method400adjusts a vehicle wheel torque according to the minimum wheel torque request. In one example, method400adjusts powertrain torque according to a relationship between a mapped driver demand wheel torque input and a commanded or requested driver demand wheel torque (e.g., as shown inFIG.2). The relationship may include a lead-in region. The wheel torque in the lead-in region may include a minimum wheel torque. Method400adjusts torque output of a torque source (e.g., internal combustion engine or electric machine) to provide the minimum wheel torque request. For example, method400may adjust a throttle position, fuel injection timing, spark, and cam timing so that the engine delivers the minimum wheel torque request. Alternatively, or in addition, method400may adjust output of an electric machine via adjusting output of an inverter that supplies electrical current to the electric machine. Method400proceeds to exit after wheel torque request is adjusted by the minimum wheel torque request for zero or non-zero application of a propulsion pedal. The minimum wheel torque is delivered when there is zero propulsion pedal input (e.g., the propulsion pedal is not applied). Minimum wheel torque is not targeted to be delivered while it serves as a reference torque for wheel torque determination during the lead-in phase for a driver propulsion pedal tip-in (e.g., increasing propulsion pedal input).

Method400may generate consistent wheel torque during vehicle coasting conditions, vehicle creep condition, and transitions between vehicle coasting conditions and vehicle creep conditions irrespective of which one or more powertrain propulsion sources generates the consistent wheel torque. For example, method400may generate consistent wheel torque when a vehicle is coasting via an electric machine. Further, method400may generate the consistent wheel torque when the vehicle is coasting via an internal combustion engine and one or more electric machines. Likewise, method400may generate a consistent wheel torque when the vehicle is creeping solely via an electric machine, via an internal combustion engine and an electric machine, or via a plurality of electric machines. Further still, method400may generate consistent wheel torque when moving or transitioning from coasting to creeping or vice-versa solely via an electric machine, via an internal combustion engine and one or more electric machines.

Thus, the method ofFIG.4provides for a method for operating a vehicle, comprising: generating consistent wheel torque during vehicle coasting conditions, vehicle creep condition, and transitions between vehicle coasting conditions and vehicle creep conditions irrespective which of one or more powertrain propulsion sources generates the consistent wheel torque. The method further comprises: selecting a minimum wheel torque from a plurality of torques; including the minimum wheel torque in a relationship between a mapped driver demand wheel torque and a driver demand wheel torque request; and adjusting torque of one or more powertrain propulsion source via a controller as a function of the relationship between the mapped driver demand wheel torque and the driver demand wheel torque request to generate the consistent wheel torque. The method includes where the one or more powertrain propulsion sources includes an internal combustion engine. The method includes where the one or more powertrain propulsion source includes an electric machine. The method includes where the minimum wheel torque is a maximum value of the plurality of torques. The method includes where the plurality of torques includes a vehicle coasting drivability wheel torque. The method includes where the plurality of torques includes a powertrain capable minimum wheel torque. The method includes where the plurality of torques includes a creep wheel torque request. The method includes where the consistent wheel torque is provided via more than one driveline configuration.

The method ofFIG.4also provides for a method for operating a vehicle, comprising: adjusting a minimum wheel torque to a creep wheel torque request in a first phase; adjusting the minimum wheel torque to a smooth transition wheel torque in a second phase; adjusting the minimum wheel torque to a vehicle coasting drivability torque in a third phase; and adjusting torque of powertrain propulsion sources via a controller in response to the minimum wheel torque. The method includes where the first, second, and third phases are defined as a function of vehicle speed. The method includes where the second phase lies between the first phase and the second phase, and where the smooth transition wheel torque is a predetermined wheel torque rate of change. The method includes where the vehicle coasting drivability wheel torque is provided via one or more propulsion sources to deliver consistent vehicle deceleration during vehicle coasting.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example examples described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.