Patent Description:
A drive axle system having electric motors is disclosed in <CIT>. <CIT> discloses a clutch control system for a motorcycle that controls operation of a clutch that connects a crankshaft of an internal combustion engine to a six-speed countershaft transmission such that the clutch control system prevents torque from being provided to a motorcycle wheel when the engine may stall or when the transmission is not in gear.

In at least one embodiment a method of controlling an axle assembly is provided. The axle assembly has a transmission, an electric motor, a clutch, and a clutch actuator. The transmission has a set of gears. The electric motor provides torque to the transmission. The motor has a rotor that is rotatable about an axis. The rotor is operatively connected to the transmission. The clutch is selectively engageable with a member of the set of gears. The clutch actuator is configured to actuate the clutch. The method includes executing a speed synchronization mode that modifies a rotational speed of the rotor without clipping the torque that is provided by the electric motor so that the rotational speed of the rotor becomes closer to the rotational speed of the clutch. The method also includes operating the clutch actuator to shift the clutch from a neutral position toward an engaged position. The method also includes determining whether the clutch is shifted from the neutral position to the engaged position within a first predetermined period of time.

The clutch is disengaged from the set of gears when in the neutral position. The clutch is shifted to the engaged position when teeth of the clutch mesh with teeth of the member of the set of gears. The clutch may couple the member of the set of gears to a shaft when the clutch is in the engaged position.

Determining whether the clutch is shifted from the neutral position to the engaged position may be based on a signal from the clutch actuator. Determining whether the clutch is shifted from the neutral position to the engaged position may be based on a signal from a clutch position sensor. The signal from the clutch position sensor may be indicative of a position of the clutch.

The method may include stopping operation of the clutch actuator that shifts the clutch from the neutral position toward the engaged position when shifting of the clutch is completed within the first predetermined period of time.

The method may include executing a low torque synchronization mode when the clutch is not shifted from the neutral position to the engaged position within the first predetermined period of time.

The clutch actuator may continue to actuate the clutch from the neutral position toward the engaged position when the low torque synchronization mode is executed and the first predetermined period of time has elapsed.

Executing the low torque synchronization mode may include adjusting the rotational speed of the rotor to track a rotational speed of the clutch while limiting output torque of the electric motor. Limiting output torque of the electric motor may prevent unintended acceleration or deceleration when the clutch meshes with the member of the set of gears.

The method may include determining whether the clutch is shifted from the neutral position to the engaged position within a second predetermined period of time when the low torque synchronization mode is executed. The first predetermined period of time may differ from the second predetermined period of time.

The method may include stopping operation of the clutch actuator that shifts the clutch from neutral position toward the engaged position when shifting of the clutch is completed within the second predetermined period of time.

The method may include operating the clutch actuator to actuate the clutch to the neutral position when shifting of the clutch is not completed within the second predetermined period of time. The method may include providing an error signal when shifting of the clutch is not completed within the second predetermined period of time.

It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms.

Referring to <FIG>, an example of a vehicle <NUM> is shown. The vehicle <NUM> may be a motor vehicle like a truck, farm equipment, military transport or weaponry vehicle, or cargo loading equipment for land, air, or marine vessels. The vehicle <NUM> may include a trailer for transporting cargo in one or more embodiments. The vehicle <NUM> may include a drive axle system <NUM>.

The drive axle system <NUM> includes one or more axle assemblies, such as a front axle assembly <NUM> and a rear axle assembly <NUM>. The front axle assembly <NUM> and the rear axle assembly <NUM> are illustrated as drive axle assemblies. A drive axle assembly may be configured to provide torque to one or more wheel assemblies <NUM> that may be rotatably supported on the axle assembly. A wheel assembly <NUM> may include a tire disposed on a wheel. The drive axle system <NUM> may also include or be associated with a power source <NUM>, such as an electrical power source like a battery.

In at least one configuration, the front axle assembly <NUM> and the rear axle assembly <NUM> may generally be disposed near each other and may be positioned toward the rear of the vehicle <NUM>, similar to a conventional tandem axle arrangement. However, unlike a conventional tandem axle arrangement, the front axle assembly <NUM> and the rear axle assembly <NUM> are not operatively connected to each other and do not receive torque from the same electric motor. As such, the front axle assembly <NUM> and the rear axle assembly <NUM> are not connected in series with each other with a shaft, such as a prop shaft that may connect an output of the front axle assembly <NUM> with an input of the rear axle assembly <NUM>. It is also contemplated that the front axle assembly <NUM> and the rear axle assembly <NUM> may be arranged in a different manner, such as with either or both axle assemblies being disposed near the front of the vehicle.

The front axle assembly <NUM> and the rear axle assembly <NUM> may have similar or identical configurations. For example, both axle assemblies <NUM>, <NUM> include a housing assembly <NUM>, a differential assembly <NUM>, a pair of axle shafts <NUM>, an electric motor <NUM>, a transmission <NUM>, a drive pinion <NUM>, or combinations thereof. The positioning of the differential assembly <NUM>, the electric motor <NUM>, and/or the transmission <NUM> may differ from that shown. For instance, the differential assembly <NUM> may be positioned between the electric motor <NUM> and the transmission <NUM>.

The housing assembly <NUM> receives various components of the axle assembly <NUM>, <NUM>. In addition, the housing assembly <NUM> may facilitate mounting of the axle assembly to the vehicle <NUM>.

The axle housing <NUM> may receive and support the axle shafts <NUM>. In at least one configuration, the axle housing <NUM> may include a center portion <NUM> and at least one arm portion <NUM>.

The center portion <NUM> may be disposed proximate the center of the axle housing <NUM>. The center portion <NUM> may define a cavity that may receive the differential assembly <NUM>.

One or more arm portions <NUM> may extend from the center portion <NUM>. For example, two arm portions <NUM> may extend in opposite directions from the center portion <NUM> and away from the differential assembly <NUM>. The arm portions <NUM> may each have a hollow configuration or tubular configuration that may extend around and may receive a corresponding axle shaft <NUM> and may help separate or isolate the axle shaft <NUM> from the surrounding environment. A wheel hub may be rotatably disposed on an arm portion <NUM> and operatively connected to an axle shaft <NUM>. A wheel assembly <NUM> may be mounted to the wheel hub.

The differential carrier <NUM> may be mounted to the center portion <NUM> of the axle housing <NUM>. The differential assembly <NUM> may be rotatably supported on the differential carrier <NUM>.

The differential assembly <NUM> is disposed in the housing assembly <NUM>. For instance, the differential assembly <NUM> may be disposed in the center portion <NUM> of the axle housing <NUM>. The differential assembly <NUM> may transmit torque to the axle shafts <NUM> of the axle assembly and permit the axle shafts and wheel assemblies <NUM> to rotate at different velocities in a manner known by those skilled in the art. For example, the differential assembly <NUM> may have a ring gear <NUM> that may be fixedly mounted on a differential case. The ring gear <NUM> and the differential case may be rotatable about a differential axis. The differential case may receive differential gears that may be operatively connected to the axle shafts <NUM>.

The axle shafts <NUM> are configured to transmit torque between the differential assembly <NUM> and a corresponding wheel hub. For example, two axle shafts <NUM> may be provided such that each axle shaft <NUM> extends through a different arm portion <NUM> of axle housing <NUM>. The axle shafts <NUM> may be rotatable about an axis, such as a wheel axis or the differential axis.

The electric motor <NUM> is configured to provide torque, such as propulsion torque or regenerative braking torque. Propulsion torque may be used to propel the vehicle <NUM>, such as in a forward or backward direction. Propulsion torque may also be used to hold the vehicle in a stationary position or to help reduce or limit vehicle rollback, such as on an inclined surface. Regenerative braking may provide a regenerative braking torque, which may also be referred to as regenerative brake torque. Regenerative braking may capture kinetic energy when the electric motor <NUM> is used to brake or slow the velocity of the vehicle <NUM>. Recovered energy may be transmitted from the wheel assemblies <NUM> to drive the electric motor <NUM>. Thus, the electric motor <NUM> may function as a generator and may be used to charge the power source <NUM>. The electric motor <NUM> may be electrically connected to the power source <NUM> via an inverter in a manner known by those skilled in the art. Electrical connections between the front axle assembly <NUM> and the rear axle assembly <NUM> and the power source <NUM> are represented with connection symbols P1 and P2, respectively.

The electric motor <NUM> may be mounted to or positioned inside of the housing assembly <NUM>. The electric motor <NUM> includes a stator <NUM> and a rotor <NUM>. The stator <NUM> may be fixedly positioned with respect to the housing assembly <NUM>. The stator <NUM> may encircle the rotor <NUM>. The rotor <NUM> is rotatable about an axis <NUM> with respect to the stator <NUM>.

The transmission <NUM> facilitates the transmission of torque between the electric motor <NUM> and the drive pinion <NUM>. Torque transmission may be bidirectional. The transmission <NUM> may provide gear reduction and multiple gear ratios between the rotor <NUM> and the drive pinion <NUM>. The transmission <NUM> may be of any suitable type. For instance, the transmission <NUM> may be a countershaft transmission, an epicyclic transmission (e.g., a transmission having a planetary gear set), or the like. A countershaft transmission may include a single countershaft or multiple countershafts. Examples of an axle assembly having a single countershaft transmission are disclosed in <CIT> and <CIT>. Examples of an axle assembly having a dual countershaft transmission is disclosed in <NUM>,<NUM>,<NUM>, <NUM>,<NUM>,<NUM>, and <NUM>,<NUM>,<NUM>. Examples of an axle assembly having an epicyclic transmission are disclosed in <CIT> and <CIT>.

The transmission <NUM> may include a clutch <NUM> and a clutch actuator <NUM>.

A clutch <NUM> controls rotation of one part with respect to another part. For instance, a clutch may connect and disconnect two parts, such as a driving part and a driven part. A clutch <NUM> facilitates the engagement and disengagement of a component of the transmission <NUM> to provide a desired gear ratio. For example, a clutch may selectively couple a gear of a countershaft transmission to a shaft to permit torque transmission via that gear, and hence with an associated gear ratio, and may disengage or be decoupled from that gear to disable torque transmission via that gear. Similarly, a clutch may engage a component of an epicyclic gear set, such as a sun gear, to provide a first gear ratio and may engage another component, such as a planet gear carrier, to provide a second gear ratio. It is contemplated that the same clutch or different clutches may be used to provide different gear ratios. For simplicity, the clutch <NUM> will primarily be described in the context of a clutch that may move with respect to the drive pinion <NUM> or slide along the drive pinion <NUM> between a neutral position and an engaged position.

A clutch may have any suitable configuration. For example, a clutch <NUM> may be configured as a friction clutch, like a dog clutch or a spline clutch. An example of a clutch <NUM> is shown in <FIG> that is configured as a dog clutch. In such a configuration, the clutch <NUM> may be configured to slide along a shaft <NUM>, such as a shaft of the drive pinion <NUM>. The clutch <NUM> may include a clutch hole <NUM>, a clutch spline <NUM>, a clutch groove <NUM>, and a clutch gear <NUM>.

The clutch hole <NUM> may extend through the clutch <NUM> and may extend around the shaft <NUM>.

The clutch spline <NUM> may be disposed in the clutch hole <NUM>. The clutch spline <NUM> may mate with a spline <NUM> on the shaft <NUM>. The mating splines may allow the clutch <NUM> to move in an axial direction along a shaft <NUM> while inhibiting rotation of the clutch <NUM> with respect to the shaft <NUM>. Thus, the clutch <NUM> may be rotatable about an axis (e.g., axis <NUM>) with the shaft <NUM>.

The clutch groove <NUM>, if provided, may face away from the clutch hole <NUM> and may be configured to receive a linkage, such as a shift fork, that may operatively connect the clutch <NUM> to the clutch actuator <NUM>.

The clutch gear <NUM> may have teeth that may be configured to mate with corresponding teeth on a gear <NUM>, such as a gear of the transmission <NUM>. It is also contemplated the that teeth of the clutch gear <NUM> and clutch engagement teeth <NUM> of the gear <NUM> may be configured like a spline and may be received inside a hole in the gear <NUM> between the shaft <NUM> and the gear <NUM> to selectively couple the gear <NUM> to the shaft <NUM>. The clutch engagement teeth <NUM> differ from teeth of the gear <NUM> that may mesh with teeth of another gear of the transmission <NUM>.

The clutch <NUM> is positionable in a neutral position and an engaged position. An example of a neutral position is shown in <FIG>. The clutch <NUM> may be disengaged from gears of the transmission <NUM>, such as gear <NUM>, when in the neutral position. As such, the clutch <NUM> may be spaced apart from the gear <NUM> and the gear <NUM> may be rotatable with respect to the clutch <NUM> and the shaft <NUM>. An example of an engaged position is shown in <FIG>. The clutch <NUM> may engage a gear of the transmission <NUM>, such as gear <NUM>, such that teeth of the clutch gear <NUM> mesh with clutch engagement teeth <NUM> of the gear <NUM>.

The clutch actuator <NUM> may actuate the clutch <NUM>. For instance, the clutch actuator <NUM> may actuate the clutch <NUM> between the neutral position and the engaged position. In at least one configuration, the clutch actuator <NUM> may move the clutch <NUM> along an axis, such as the axis <NUM>, a countershaft axis, or the like. The clutch actuator <NUM> may be mounted on or inside the housing assembly <NUM>.

Referring to <FIG>, the drive pinion <NUM> operatively connects the differential assembly <NUM> and the transmission <NUM>. The drive pinion <NUM> may be received in the housing assembly <NUM> and may transmit torque between the differential assembly <NUM> and a transmission <NUM>. The drive pinion <NUM> may be rotatable about an axis, such as the axis <NUM>, and may have a gear portion that has teeth that meshes with teeth of the ring gear <NUM> of the differential assembly <NUM>. The shaft <NUM> may extend from the gear portion. Torque may be transmitted between the transmission <NUM> and the drive pinion <NUM> when the drive pinion <NUM> is operatively connected to the transmission <NUM>. For example, torque that is provided from the electric motor <NUM> to the transmission <NUM> and to the drive pinion <NUM> may be transmitted to the ring gear <NUM> and thus to the differential assembly <NUM>.

A control system <NUM> controls operation of the drive axle system <NUM>. For example, the control system <NUM> may include one or more microprocessor-based control modules or controllers <NUM> that may be electrically connected to or communicate with components of the vehicle <NUM> and/or the axle assemblies <NUM>, <NUM>, such as the electric motors <NUM> and clutch actuators <NUM>. Control system connections are represented by the double arrowed lines in <FIG> as well as by connection symbols A, B, C, and D. The control system <NUM> may also monitor and control the power source <NUM>. In addition, the control system <NUM> may also process input signals or data from various input devices or sensors. These input devices may include a first speed sensor <NUM>, a second speed sensor <NUM>, a clutch position sensor <NUM>, an operator communication device <NUM>, or combinations thereof.

The first speed sensor <NUM> may detect or provide a signal indicative of the rotational speed or rotational velocity of a rotatable component disposed upstream from the clutch <NUM>, such as the rotor <NUM> or a gear of the transmission <NUM>.

The second speed sensor <NUM> may detect or provide a signal indicative of the rotational speed or rotational velocity of the clutch <NUM> or a rotatable component disposed downstream from the clutch <NUM>, such as the drive pinion <NUM>, the differential assembly <NUM>, an axle shaft <NUM>, a wheel hub or the like. The first speed sensor <NUM> and the second speed sensor <NUM> may be used in conjunction to determine when the rotational speed of the clutch <NUM> is sufficiently synchronized with the rotational speed of another component, such as a transmission gear like gear <NUM>, to permit movement or shifting of the clutch <NUM>. Accordingly, the terms "synchronized" or "sufficiently synchronized" mean that the rotational speed of two components may be sufficiently close so as to permit the clutch <NUM> to be shifted and may not require exactly the same rotational speed.

The clutch position sensor <NUM> is configured to provide a signal indicative of the position of the clutch <NUM>. For instance, the signal may be indicative as to whether the clutch <NUM> is in the neutral position or the engaged position. The clutch position sensor <NUM> may directly or indirectly detect or generate a signal indicative of the position of the clutch <NUM>. For instance, the clutch position sensor <NUM> may be a proximity sensor or the like that may directly detect the position of the clutch <NUM>. Alternatively, the clutch position sensor <NUM> may indirectly detect the position of the clutch <NUM>, such as by detecting the stroke or actuation distance of the clutch actuator <NUM> or number of revolutions of a shaft of the clutch actuator <NUM> when the clutch actuator <NUM> is configured to rotate to actuate the clutch <NUM>. In such a configuration, the signal may be provided by the clutch actuator <NUM> or may be based on an operating attribute of the clutch actuator <NUM>.

The operator communication device <NUM> may be provided to receive an input from an operator or vehicle driver and/or provide information to an operator. The operator communication device <NUM> may be of any suitable type or types, such as a switch, button, sensor, display, touchscreen, keypad, voice command or speech recognition system, or the like. The operator communication device <NUM> may be used to input data that may not be predetermined or provided by a sensor or other input device. In addition, the operator communication device <NUM> may be configured to provide information to the operator, such as a warning or alert that a gear shift has not been completed. Information may be provided to an operator in one or more formats, such as an audible format, visual format, and/or haptic format.

Referring to <FIG>, a flowchart of a method of controlling an axle assembly is shown. As will be appreciated by one of ordinary skill in the art, the flowcharts may represent control logic which may be implemented or affected in hardware, software, or a combination of hardware and software. For example, the various functions may be affected by a programmed microprocessor. The control logic may be implemented using any of a number of known programming and processing techniques or strategies and is not limited to the order or sequence illustrated. For instance, interrupt or event-driven processing may be employed in real-time control applications rather than a purely sequential strategy as illustrated. Likewise, parallel processing, multitasking, or multi-threaded systems and methods may be used.

Control logic may be independent of the particular programming language, operating system, processor, or circuitry used to develop and/or implement the control logic illustrated. Likewise, depending upon the particular programming language and processing strategy, various functions may be performed in the sequence illustrated, at substantially the same time, or in a different sequence while accomplishing the method of control. The illustrated functions may be modified, or in some cases omitted, without departing from the scope of the present invention. Method steps may be executed by the control system <NUM> and may be implemented as a closed loop control system.

As an overview, a vehicle that has an axle assembly that has a multi-speed transmission and a corresponding electrical motor can be controlled to facilitate transmission gear shifts, such as an upshift from a first gear ratio (e.g., low speed gear ratio) to a second gear ratio (e.g., a higher speed gear ratio) and downshifts from a second gear ratio to a first gear ratio. The method attempts to conduct a gear shift (upshift or downshift) by executing a speed synchronization mode that modifies the rotational speed of the rotor without clipping (e.g., altering, limiting, or modifying) the torque provided by the electric motor. As a result, electric motor may be able to quickly resume providing the desired or requested level of torque once a gear shift is completed. The clutch may be shifted from one gear ratio to another if sufficient synchronization of the rotational speed of the clutch and the rotational speed of the gear that is to be engaged is obtained.

If sufficient synchronization is not achieved, then the method may execute a low torque synchronization mode that modifies the rotational speed of the rotor while clipping or modifying the output torque of the electric motor. The clutch may be shifted from one gear ratio to another if sufficient synchronization of the rotational speed of the clutch and the rotational speed of the gear that is to be engaged is obtained. If sufficient synchronization is not obtained, then the shift may be aborted.

The method steps shown in <FIG> are used to coordinate and execute a gear upshift or a gear downshift. For illustration purposes, the method is described under the following initial operational conditions. First, the rotor of the electric motor is rotating about its axis. Second, the clutch is in the neutral position. In the neutral position, the clutch can rotate about an axis but is not in meshing engagement with a gear of the transmission. The clutch may be spaced apart from the gears of the transmission such that teeth of the clutch may not contact corresponding teeth of the gear of the transmission when the clutch is in the neutral position. In other words, the clutch is spinning but is disengaged from the transmission gears. As a result, the clutch and the transmission gears may be rotating at different speeds. Third, it is desired to shift the clutch from the neutral position into meshing engagement with a gear of the transmission.

Shifting a clutch from the neutral position when the rotor is spinning requires sufficient synchronization between the clutch and the transmission gear to be engaged. Sufficient synchronization include sufficient velocity synchronization and sufficient positional synchronization. Sufficient velocity synchronization is achieved when the clutch and the gear that is to be engaged by the clutch are rotating in the same direction at speeds that are sufficiently close to permit the teeth of the clutch (e.g., teeth of the clutch gear <NUM>) to mesh with corresponding teeth of the gear (e.g., clutch engagement teeth <NUM>). Sufficient positional synchronization is achieved when the teeth of the clutch are sufficiently aligned with gaps between corresponding teeth of the gear to permit the teeth of the clutch to be moved into gaps between corresponding teeth of the gear so that the clutch teeth and corresponding gear teeth may mate and mesh. Sufficient velocity synchronization and sufficient positional synchronization are unlikely to be present without intervention that modifies the rotational speed of the rotor.

At block <NUM>, a speed synchronization mode is executed. The speed synchronization mode is executed by adjusting the rotational speed of the rotor <NUM> to attempt to match or sufficiently synchronize the rotational speed of the clutch <NUM> with the rotational speed of the gear that is to be engaged by the clutch <NUM>. In addition, the torque provided by the electric motor <NUM> may not be clipped. The rotational speed of the rotor <NUM> may be based on a signal from a speed sensor, such as the first speed sensor <NUM>. The rotational speed of the clutch <NUM> may be based on a signal from another speed sensor, such as the second speed sensor <NUM>.

At block <NUM>, the clutch <NUM> is actuated. The clutch <NUM> may be actuated by operating the clutch actuator <NUM> to shift the clutch <NUM> from the neutral position toward the gear that is to be clutched or engaged. For instance, the clutch actuator <NUM> may shift the clutch <NUM> toward an engaged position in which the teeth of the clutch <NUM> (e.g., teeth of the clutch gear <NUM>) would mate or mesh with the teeth (e.g., clutch engagement teeth <NUM>) of the gear that is to be engaged. The clutch <NUM> may advance or move the engaged position when there is sufficient velocity synchronization and sufficient positional synchronization between the clutch <NUM> and the transmission gear to be engaged.

At block <NUM>, the method determines whether the shift is completed within a first predetermined period of time. A shift may be completed when there is sufficient velocity and positional synchronization between the clutch <NUM> and the transmission gear to be engaged and the clutch <NUM> is moved by the clutch actuator <NUM> to a position where the teeth of the clutch <NUM> mate or mesh with the teeth of the gear. Completion of a shift may be based on a signal from the from the clutch position sensor <NUM>. For instance, a shift may be complete when the clutch <NUM> has moved along its rotational axis by a distance that indicates that there is meshing engagement between the teeth of the clutch gear <NUM> and corresponding clutch engagement teeth <NUM>. A shift may not be complete when the clutch has moved along its rotational axis by a lesser distance, which may be indicative of a blocked shift in which teeth of the clutch (e.g., teeth of the clutch gear <NUM>) have not been inserted into corresponding gaps between teeth of the transmission gear (e.g., gaps between the clutch engagement teeth <NUM>). A blocked shift may be indicative that sufficient velocity synchronization, sufficient positional synchronization, or both have not been obtained. The first predetermined period of time may be a constant or variable amount that may be based on performance attributes of the axle assembly or vehicle development testing. As a nonlimiting example, the first predetermined period of time may be two seconds or less. If the shift is completed within the first predetermined period of time, then the method may continue at block <NUM>. If the shift is not completed within the first predetermined period of time, then the method may continue at block <NUM>.

At block <NUM>, the clutch <NUM> has moved to the engaged position in the shift is complete. As a result, the clutch actuator <NUM> does not need to continue to exert an actuation force on the clutch <NUM> that urges the clutch <NUM> toward the engaged position. Thus, operation of the clutch actuator <NUM> that urges the clutch toward the engaged position is stopped or set to a neutral state in which the clutch actuator <NUM> does not urge the clutch to move toward or away from the engaged position, thereby helping improve the life of the clutch actuator <NUM> and reducing energy consumption.

At block <NUM>, a low torque synchronization mode is executed. The low torque synchronization mode may be executed by continuing to exert an actuation force on the clutch <NUM> with the clutch actuator <NUM> that urges the clutch <NUM> toward the engaged position. In other words, the clutch actuator <NUM> continues to be operated to attempt to complete a gear shift if the speed synchronization mode is not successful. In addition, the low torque synchronization mode is executed by continuing to attempt to match or sufficiently synchronize the rotational speed of the clutch <NUM> with the rotational speed of the gear that is to be engaged by the clutch <NUM> by adjusting the rotational speed of the rotor <NUM>. However, unlike the speed synchronization mode, the torque that is provided by the electric motor <NUM> is clipped. As such, the rotational speed of the rotor <NUM> may track the rotational speed of the clutch <NUM> but with limited torque to prevent unintended acceleration or deceleration in the event that sufficient synchronization is achieved to move the clutch <NUM> to the engaged position. The rotational speed of the rotor <NUM> may be based on a signal from a speed sensor, such as the first speed sensor <NUM> as previously discussed. Similarly, the rotational speed of the clutch <NUM> may be based on a signal from another speed sensor, such as the second speed sensor <NUM>.

At block <NUM>, the method determines whether the shift is completed within a second predetermined period of time. A shift may be completed when sufficient velocity and positional synchronization between the clutch <NUM> and the transmission gear to be engaged is achieved and the clutch <NUM> is moved by the clutch actuator <NUM> to a position where the teeth of the clutch mate or mesh with the teeth of the gear. Completion of a shift may be based on a signal from the clutch position sensor <NUM> as previously discussed. The second predetermined period of time may be a constant or variable amount that may be based on performance attributes of the axle assembly were vehicle development testing. The second predetermined period of time may be the same as or may differ from the first predetermined period of time. As a nonlimiting example, the second predetermined period of time may be two seconds. It is contemplated that the second predetermined period of time may be greater than the first predetermined period of time there may be a greater likelihood of successfully completing a shift under the low torque synchronization mode. If the shift is completed within the second predetermined period of time, then the method may continue at block <NUM>. If the shift is not completed within the second predetermined period of time, and the method may continue at block <NUM>.

At block <NUM>, the shift may be aborted. Aborting the shift may include operating the clutch actuator <NUM> to actuate the clutch <NUM> back to the neutral position. Moving the clutch <NUM> back to the neutral position may help prevent overheating of the clutch actuator <NUM> and potential wear of the clutch <NUM> and/or the gear that was to be engaged. Aborting the shift may also include providing an error signal. The error signal may trigger a notification to the vehicle operator via the operator communication device <NUM>, a diagnostic code to facilitate assessment and maintenance, or both.

The present invention allows an axle assembly to be controlled with a speed synchronization mode to attempt to complete a gear shift without clipping or modifying torque provided by the electric motor, which may improve responsiveness and allow a desired level of torque to be provided more rapidly once a shift is completed. The amount of time attempt to complete a gear shift using the speed synchronization mode may allow the torque provided by the electric motor to better match the torque requested by a vehicle operator, thereby helping improve responsiveness of the axle assembly after a shift is completed. The present invention provides an additional low torque synchronization mode in the event that a shift is not completed using the speed synchronization mode, thereby controlling the electric motor in a different manner that may improve the likelihood of successfully completing a gear shift.

Claim 1:
A method of controlling an axle assembly (<NUM>, <NUM>), the axle assembly comprising a transmission (<NUM>) that has a set of gears, an electric motor (<NUM>) that provides torque to the transmission (<NUM>), the electric motor (<NUM>) comprising a rotor (<NUM>) that is rotatable about an axis (<NUM>) and is operatively connected to the transmission (<NUM>), a clutch selectively engageable with a member of the set of gears, and a clutch actuator (<NUM>) configured to actuate the clutch (<NUM>), the method comprising the steps of:
executing a speed synchronization mode that modifies a rotational speed of the rotor (<NUM>) of the electric motor (<NUM>) of the axle assembly without clipping torque provided by the electric motor (<NUM>) so that the rotational speed of the rotor (<NUM>) becomes closer to the rotational speed of the clutch (<NUM>) of the axle assembly;
operating the clutch actuator (<NUM>) to shift the clutch (<NUM>) from a neutral position toward an engaged position; and
determining whether the clutch (<NUM>) is shifted from the neutral position to the engaged position within a first predetermined period of time.