Method and apparatus for operating a vehicle employing non-combustion torque machine

A vehicle including a powertrain system that includes an electric machine electrically connected to a power inverter is described, wherein the powertrain system is operative in an electric vehicle mode to generate propulsion torque. A method for controlling the powertrain system includes determining a vehicle speed, and determining a preferred audible sound to be generated by the powertrain system when operating in the electric vehicle mode at the vehicle speed. A control signal for the power inverter is determined, and is associated with operating the powertrain system in the electric vehicle mode at the vehicle speed. The preferred audible sound is incorporated into the control signal for the power inverter, and the power inverter is controlled to operate the electric machine employing the control signal and the preferred audible sound.

TECHNICAL FIELD

The present disclosure relates to vehicles employing non-combustion torque machines, and control thereof.

BACKGROUND

A vehicle operating in an electric vehicle mode may emit less audible noise than a vehicle employing an internal combustion engine for propulsion power. Noise emission from a vehicle may serve to audibly locate the vehicle, and provide information about the vehicle's acceleration, deceleration, and/or direction of travel.

SUMMARY

A vehicle including a powertrain system that includes an electric machine electrically connected to a power inverter is described, wherein the powertrain system is operative in an electric vehicle mode to generate propulsion torque. A method for controlling the powertrain system includes determining a vehicle speed, and determining a preferred audible sound to be generated by the powertrain system when operating in the electric vehicle mode at the vehicle speed. A control signal for the power inverter is determined, and is associated with operating the powertrain system in the electric vehicle mode at the vehicle speed. The preferred audible sound is incorporated into the control signal for the power inverter, and the power inverter is controlled to operate the electric machine employing the control signal and the preferred audible sound.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,FIG. 1schematically shows an embodiment of a vehicle100including a multi-mode powertrain system20coupled to a driveline60and controlled by a control system10, wherein a rechargeable on-board high-voltage electrical energy storage device (DC power source)25supplies energy to generate at least a portion of the propulsion power. In certain embodiments, the DC power source25may electrically connect via an on-vehicle battery charger24to a remote, off-vehicle electric power source for charging while the vehicle100is stationary. Like numerals refer to like elements throughout the description. The concepts described herein apply to any vehicle powertrain system that includes a non-combustion torque machine that is operable to generate propulsion power. This includes, by way of non-limiting examples, plug-in hybrid vehicles, electric vehicles and non-plug-in hybrid vehicles. As used herein, the term “vehicle” refers to any mobile platform, and may include, by way of non-limiting examples, a passenger vehicle, a light-duty or heavy-duty truck, a utility vehicle, an agricultural vehicle, an industrial or warehouse vehicle, or a recreational off-road vehicle.

The illustrated powertrain system20includes multiple torque-generating devices including an internal combustion engine (engine)40and first and second electrically-powered torque machines (electric machines)34,36, respectively, that rotatably couple to a gear train50. In one embodiment, the gear train50is a simple planetary gear set including a sun gear52, a plurality of planet gears coupled to a carrier54, and a ring gear56. An output member62couples between the gear train50and a driveline60. Thus, the engine40and the first and second electric machines34,36couple to the gear train50and are controllable to generate propulsion power that is transferred to the driveline60as propulsion torque for the vehicle100in response to an acceleration request, or braking torque for the vehicle100in response to a braking request. The powertrain system20may operate in an electric vehicle (EV) mode, an electrically-variable transmission (EVT) mode, or a fixed-gear mode. When the powertrain system20is operating in the EV mode, propulsion power is generated by one or both the first and second electric machines34,36, and the engine40is in an OFF state.

One embodiment of the engine40and the first and second electric machines34,36that couple to the gear train50and generate output torque that is transferred to the driveline60to generate propulsion torque is now described. A crankshaft44of the engine40couples to an input member41that couples to a rotor of the first electric machine34via a third clutch55. In one embodiment and as shown an output member from the rotor of the first electric machine34couples via a second clutch53to the ring gear56, the second electric machine36rotatably couples to the sun gear52, and the planet gear carrier54couples via the output member62to the driveline60. The ring gear56is couplable via a first clutch/brake51to a chassis ground. A transmission controller (TCM) monitors rotational speeds of various rotating members and controls activations of the first, second and third clutches51,53and55.

The engine40is preferably a multi-cylinder internal combustion engine that converts hydrocarbon-based fuel or another fuel to mechanical torque through a thermodynamic combustion process. The engine40is equipped with a plurality of actuators and sensing devices for monitoring operation and delivering fuel to form in-cylinder combustion charges that generate an expansion force that is transferred via pistons and connecting rods to the crankshaft44to produce torque. Operation of the engine40is controlled by an engine controller (ECM)45. The engine40may be configured to execute autostart and autostop control routines, fuel cutoff (FCO) control routines and cylinder deactivation control routines during ongoing operation of the powertrain system20. The engine40is considered to be in an OFF state when it is not rotating. The engine40is considered to be in an ON state when it is rotating, including one or more FCO states in which it is spinning and unfueled.

The first and second electric machines34,36are preferably high-voltage multi-phase electric motor/generators that electrically connect to the DC power source25via first and second inverter modules33,35, respectively. The first and second electric machines34,36are configured to convert stored electric energy to mechanical power and convert mechanical power to electric energy that may be stored in the DC power source25. The DC power source25may be any high-voltage energy storage device, e.g., a multi-cell lithium ion device, an ultracapacitor, or another suitable device without limitation. The DC power source25may be characterized in terms of its energy capacity, e.g., state of charge (SOC), which may be expressed in terms of Amp-hours (Ah) or percentage of a maximum charge (%). Determination of energy capacity, e.g., SOC, for a battery or another energy storage device is known to those skilled in the art and not described in detail herein. In one embodiment, the DC power source25may electrically connect via the on-vehicle battery charger24to a remote, off-vehicle electric power source for charging while the vehicle100is stationary, with the on-vehicle battery charger24controlled by a charger controller21. The DC power source25electrically connects to the first inverter module33via a high-voltage DC bus29to transfer high-voltage DC electric power to the first electric machine34in response to control signals originating in the control system10. Likewise, the DC power source25electrically connects to the second inverter module35via the high-voltage DC bus29to transfer high-voltage DC electric power to the second electric machine36in response to control signals originating in the control system10. The remote, off-vehicle electric power source may be any public/commercial power source or private power source, such as a residential power source.

Each of the first and second electric machines34,36includes the rotor and a stator, and electrically connects to the DC power source25via the corresponding first and second inverter modules33,35, respectively, and the high-voltage DC bus29. The first and second inverter modules33,35are both configured with suitable control circuits including complementary paired switch devices in the form of power transistors, e.g., Insulated Gate Bipolar Transistors (IGBTs) for transforming high-voltage DC electric power to high-voltage AC electric power and transforming high-voltage AC electric power to high-voltage DC electric power. Alternatively, Field-Effect Transistors (FETs), MOSFETs, or other power transistors may be employed.

The first and second inverter modules33,35are preferably configured as voltage-source inverters (VSI) that may operate in either a pulsewidth-modulated (PWM) VSI mode or a six-step VSI mode to convert stored DC electric power originating in the DC power source25to AC electric power to drive the respective first and second electric machines34,36to generate torque. Similarly, each of the first and second inverter modules33,35converts mechanical power transferred to the respective first and second electric machines34,36to DC electric power to generate electric energy that is storable in the DC power source25, including as part of a regenerative power control strategy. The first and second inverter modules33,35are both configured to receive motor control commands and control inverter states to provide the motor drive and regenerative braking operations through the first and second electric machine34,36. In one embodiment, a DC/DC electric power converter23electrically connects to a low-voltage bus28and a low-voltage battery27, and electrically connects to the high-voltage DC bus29. Such electric power connections are known and not described in detail. The low-voltage battery27electrically connects to an auxiliary power system26to provide low-voltage electric power to low-voltage systems on the vehicle, including, e.g., electric windows, HVAC fans, seats and other devices. Each of the first and second inverter modules33,35may also include other electric circuit elements such as high-voltage DC link capacitors, resistors, and active DC bus discharge circuits.

The first and second inverter modules33,35include gate drive modules. Each of the gate drive modules include a plurality of paired gate drive circuits, each which signally individually connects to one of the complementary paired switch devices of one of the phases of the respective one of the first and second inverter modules33,35. There are three paired gate drive circuits or a total of six gate drive circuits in each of the gate drive modules when the corresponding electric machine is a three-phase device. The gate drive modules receive operating commands from the controller12via communications bus18and control activation and deactivation of each of the switch devices via the gate drive circuits to provide motor drive or electric power generation functionality that is responsive to operating commands. During operation, each of the gate drive modules generates a pulse in response to a control signal originating from the controller12, which activates one of the switch devices and induces current flow through a half-phase of the respective electric machine. The first and second gate drive modules operate to periodically and repetitively sequentially activate the complementary paired switch devices to transfer electric power between one of the positive and negative rails of the high-voltage DC power bus29and a plurality of windings associated with one of the phases of the corresponding first and second torque machine34,36to transform electric power to mechanical torque, or to transform mechanical torque to electric power.

The driveline60may include a differential gear device65that mechanically couples to an axle, transaxle or half-shaft64that mechanically couples to a wheel66in one embodiment. The driveline60transfers propulsion torque between the gear train50and a road surface.

An operator interface14of the vehicle100includes a controller that signally connects to a plurality of human/machine interface devices through which the operator commands operation of the vehicle100. The human/machine interface devices preferably include, e.g., an accelerator pedal15, a brake pedal16and a user interface such as a graphical user interface (UI)17. Other human/machine interface devices may include an ignition switch to enable an operator to operate the vehicle100, a steering wheel, a transmission range selector and a headlamp switch. The accelerator pedal15provides signal input indicating an accelerator pedal position and the brake pedal16provides signal input indicating a brake pedal position. The accelerator pedal position corresponds to an operator request for acceleration in the form of propulsion torque, which may be generated by controlling operation of one or more of the first and second electric machines34,36and the engine40. The brake pedal position corresponds to an operator request for braking torque, which may be generated by controlling operation of one of the first and second electric machines34,36and the wheel brakes. In certain embodiments, a navigation system with on-vehicle GPS is employed on the vehicle100.

The control system10includes a controller12that signally connects to the operator interface14. The controller12preferably includes a plurality of discrete devices that are co-located with the individual elements of the powertrain system20to effect operational control of the individual elements of the powertrain system20in response to operator commands and powertrain demands. The controller12may also include a control device that provides hierarchical control of other control devices. The controller12communicatively connects to each of the DC power source25, the first and second inverter modules33,35, the ECM45, and the TCM, either directly or via a communication bus18to monitor and control operation thereof. The controller12commands operation of the powertrain system20, including selecting and commanding operation in one of a plurality of operating modes to generate and transfer torque between the torque generative devices, e.g., the engine40and the first and second electric machines34,36and the driveline60.

The terms controller, control module, module, control, control unit, processor and similar terms refer to any one or various combinations of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s), e.g., microprocessor(s) and associated non-transitory memory component in the form of memory and storage devices (read only, programmable read only, random access, hard drive, etc.). The non-transitory memory component is capable of storing machine readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, signal conditioning and buffer circuitry and other components that can be accessed by one or more processors to provide a described functionality. Input/output circuit(s) and devices include analog/digital converters and related devices that monitor inputs from sensors, with such inputs monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms and similar terms mean any controller-executable instruction sets including calibrations and look-up tables. Each controller executes control routine(s) to provide desired functions, including monitoring inputs from sensing devices and other networked controllers and executing control and diagnostic routines to control operation of actuators. Routines may be periodically executed at regular intervals, for example each 100 microseconds or 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation. Alternatively, routines may be executed in response to occurrence of a triggering event.

The powertrain system20communicates sensor signals and actuator command signals between the control system10, the vehicle100and the powertrain system20employing one or more communication systems and devices, including, e.g., the communication bus18, a direct connection, a local area network bus, a serial peripheral interface bus, and/or a wireless link to effect information transfer. Communication between controllers and between controllers, actuators and/or sensors may be accomplished using a direct wired link, a networked communication bus link, a wireless link or any another suitable communication link. Communication includes exchanging data signals in any suitable form, including, for example, electrical signals via a conductive medium, electromagnetic signals via air, optical signals via optical waveguides, and the like. Data signals may include signals representing inputs from sensors, signals representing actuator commands, and communication signals between controllers. The term ‘model’ refers to a processor-based or processor-executable code and associated calibration that simulates a physical existence of a device or a physical process. As used herein, the terms ‘dynamic’ and ‘dynamically’ describe steps or processes that are executed in real-time and are characterized by monitoring or otherwise determining states of parameters and regularly or periodically updating the states of the parameters during execution of a routine or between iterations of execution of the routine.

FIG. 2schematically shows an electric vehicle audible tone generation routine (routine)200that may be executed to control operation of an embodiment of a vehicle capable of operating in an EV mode. One embodiment of such a vehicle is vehicle100that is described with reference toFIG. 1. This routine200may be advantageously employed on various vehicle systems that operate in an EV mode and employ high-voltage electrical systems to generate propulsion torque. Table 1 is provided as a key wherein the numerically labeled blocks and the corresponding functions are set forth as follows, corresponding to the routine200.

TABLE 1BLOCKBLOCK CONTENTS202Is powertrain operating in EV Mode? ANDIs vehicle speed between an upper thresholdspeed and a lower threshold speed?204Determine vehicle speed206Determine a target sound associated with apreferred audible sound to be generated bythe powertrain system based upon thevehicle speed207Incorporate target sound into control ofelectric machine(s)208Determine inverter PWM frequencies thatare responsive to operating in the EV modeto dither motor operation to create anoverall baseline broadband sound that isassociated with the preferred audible sound210Determine current control and amount ofcurrent ripple that induce a desiredfrequency that generates the preferredaudible sound212Verify operation220End execution

During vehicle operation, the routine200periodically monitors operation, including determining the powertrain operating mode and monitoring vehicle speed. When the powertrain operating mode includes operating with the engine in the ON state, or when the vehicle is operating at a speed that is greater than an upper threshold speed, e.g., when the vehicle speed is greater than 20 km/h, or when the vehicle speed is less than a lower threshold speed, e.g., when the vehicle speed is less than 4 km/h, (202)(1), the present iteration of the routine200ends execution without further action (220).

When the powertrain operating mode is an EV mode, e.g., when the engine is in the OFF state, and the vehicle is operating at a speed that is between the upper and lower threshold speeds (202)(0), the routine200undertakes operation to control operation of one or more of the electric machines34,36in a manner that generates an audible tone. This includes determining the vehicle speed (204) and determining a preferred audible sound that is to be generated by the powertrain system at the vehicle speed (206). The preferred audible sound may be described in the form of a target sound, which is in the form of a complex acoustic tone that includes an audible sound that is composed from a plurality of simultaneously generated tone contributions at multiple frequencies. The complex acoustic tone may be expressed graphically and indicated as power or pressure in decibels (db) in relation to sound frequency (Hz). For purpose of this disclosure, the audible range of frequencies includes frequencies from 20 Hz to 20 kHz. In certain embodiments, the preferred audible sound is vehicle speed-dependent. A lookup table may be precalibrated that provides a plurality of preferred target sounds, wherein a vehicle speed or speed range has a unique target sound associated therewith. The lookup table may be stored in a memory device of one of the controllers and may be interrogated by the routine200. Alternatively, the target sound may be generated by an executable algorithm or formula that determines the preferred audible sound in relation to vehicle speed.

The preferred audible sound is incorporated into control of the electric machine(s), as follows (207). The preferred audible sound may be achieved as a part of executing control of one or both of the first and second electric machines34,36to generate propulsion torque that is responsive to the output torque request at the present vehicle speed. This may include determining one or more inverter PWM frequencies to dither operation to create an overall baseline broadband sound (208) and determining current controls and an amount of current ripple that induce a desired instantaneous frequency to generate a complex acoustic tone associated with the preferred audible sound for the present vehicle speed (210).

Executing dithering of the PWM control frequency to achieve a broadband base noise and executing current injection to induce current ripple to achieve pitch shifting tone that is dependent upon the vehicle speed preferably induces the preferred audible sound in operation of the first and second electric machines34,36. The operation of the first and second electric machines34,36may be monitored to verify that the desired operation is achieved (212).

FIG. 3schematically shows, with continued reference toFIG. 1, an electric motor control system110of the second inverter module35for controlling the second electric machine36, which may include executing motor dithering to achieve a broadband base noise and executing current injection to achieve pitch shifting tone that is preferably dependent upon the vehicle speed. The electric motor control system110may be executed as hardware components, integrated circuits, software control routines and/or other elements that are disposed in the second inverter module35in certain embodiments. Alternatively, certain elements of the electric motor control system110may be disposed elsewhere in the vehicle100. The electric motor control system110includes a controller150and an inverter120. Signal inputs to the controller150include the operator requests for propulsion torque and braking torque152, the present vehicle speed154, the engine state156, which may be either ON or OFF, a rotational speed of the electric machine36, and current signals from each phase115of the electric machine36.

As shown, the inverter120is disposed to provide electric control for the electric machine36, and is connected between direct current (DC) bus lines29of the DC power source25. The inverter120includes switches122,123,124,125,126,127, wherein each of the switches includes a transistor such as an IGBT that is connected in parallel with an antiparallel diode. The switches122,123,124,125,126,127operate in response to signals from the controller150supplied to gates of the transistors thereof to provide voltage to each phase115of the electric machine36. Each of the switch pairs122/125,123/126and124/127forms a phase leg of the inverter120.

A speed detection circuit160measures the rotor position and speed of the electric machine36and includes a resolver162or other speed sensing device that is coupled to the electric machine36to detect rotational position of a rotor of the electric machine36and, thereby determine a speed of the electric machine36. The speed detection circuit160may also include a resolver-to-digital converter164or another analytical scheme that converts the signals from the resolver162to digital signals (e.g., a digital motor speed signal and a digital rotor angular position signal). The resolver-to-digital converter164provides the digital representations of angular position and speed of the rotor of the electric machine36to the controller150.

The controller150includes a first torque command module172that generates commanded voltages173in response to operator requests for propulsion torque and braking torque, taking into account rotational speed of the electric machine36and current signals from each phase115of the electric machine36. This may include employing Park's transformation from three-phase to a rotating dq coordinate system to generate direct-current Cartesian commanded voltages, which includes a d-axis synchronous frame commanded voltage and a q-axis synchronous frame commanded voltage.

The controller150includes a second torque command module182that generates second commanded voltages183that may be added to corresponding ones of the first commanded voltages173in a summer174, which provides final commanded voltages175. The final commanded voltages175are presented to a transformation module176to generate three-phase voltage commands, which are employed in a transformation module190to generate control commands for the switches122,123,124,125,126,127. The second torque command module182is configured to generate the second commanded voltages183only when the vehicle speed154is less than a threshold speed, e.g., 20 km/hr, and when the engine state156is OFF, indicating the vehicle is operating in an EV mode. The second torque command module182interrogates a sound spectrum calibration table185, which provides a vehicle speed-specific predetermined motor torque command, preferably in the rotating dq coordinate system, that causes the second electric machine36to generate the complex acoustic tone that is associated with the preferred audible sound.

As such, when the second torque command module182is activated, the controller150combines the first commanded voltages173and the second commanded voltages183using the summer174to determine the final commanded voltages175. The final commanded voltages175are presented to the transformation module176to generate three-phase voltage commands, which are employed in the transformation module190to generate control commands for the switches122,123,124,125,126,127. Operation of the second electric machine36in response to the control commands for the switches122,123,124,125,126,127causes the second electric machine36to operate in a manner that generates the preferred audible sound associated with the sound spectrum calibration table185.

The sound spectrum calibration table185includes a plurality of vehicle speed-dependent target sounds. A lookup table may be precalibrated that provides the plurality of target sounds, wherein a vehicle speed or speed range has a unique target sound associated therewith. The lookup table may be stored in a memory device of one of the controllers and may be interrogated by the routine200.

The second commanded voltages183provide operational control signals that are designed to inject current into the stator to generate acoustic noise in the electric machine that corresponds to a preferred harmonic that is associated with the preferred audible sound.

FIG. 4-1graphically shows an example of characteristic operation of an electric motor supplying propulsion torque on a vehicle, including a PWM switching frequency405for control of the electric motor on the vertical axis in relation to vehicle speed410on the horizontal axis. A positive linear relationship415is shown, and indicates that the PWM switching frequency405increases linearly to achieve an increase in the vehicle speed410.

FIG. 4-2graphically shows characteristic operation of the electric motor ofFIG. 4-1in context of a select switching frequency and an associated sound pressure level (SPL), with PWM switching frequency405shown on the horizontal axis and SPL420shown on the vertical axis. SPL420is a logarithmic measure of the effective pressure of a sound relative to a reference value, and may be measured in decibels (dB). As indicated, the SPL420is at a maximum peak intensity425at a selected PWM switching frequency407, and is at or near zero at other PWM switching frequencies405.

FIG. 4-3graphically shows characteristic operation of the electric motor ofFIG. 4-1in context of a select switching frequency and an associated sound pressure level (SPL), with PWM switching frequency405shown on the horizontal axis and SPL420shown on the vertical axis, wherein dithering of the PWM switching frequency405is applied to achieve a target sound427. The dithering includes a frequency range between a lower PWM switching frequency403and an upper PWM switching frequency409, preferably about the selected switch frequency407. As indicated, a target sound427having a broadband sound spectrum is generated, with the SPL for the target sound427at or near a peak intensity over the frequency range between the lower and upper PWM switching frequencies403,409. Dithering is an intentionally applied form of noise that is employed to randomize quantization errors and smear tones into white noise, thus preventing large-scale sound patterns such as may be shown by the peak intensity425. The target sound427may be generated by applying dithering to the selected switch frequency407and injecting current. The target sound427is associated with operation of an electric machine on a vehicle, e.g., as described with reference to the electric vehicle audible tone generation routine200shown inFIG. 2.

The concepts described herein enable using electric machines to generate powertrain sounds, including using tonal and random ripple current injection strategies to make desired broadband and tonal sounds. Existing on-vehicle controllers may be employed to control and affect motor noise. This may include characterizing a sound profile of an electric machine based on current injection, and developing calibrations to tune motor control to generate the required desired tone strength at different frequencies. In certain embodiments, a broadband base noise in conjunction with a pitch shifting tone that changes in frequency with vehicle speed is accomplished by executing motor dithering to achieve the broadband base noise and executing current injection to achieve pitch shifting tone.