Patent ID: 12228203

DETAILED DESCRIPTION

In an all-wheel-drive vehicle, under constant vehicle speed conditions, power to one of the axles can be disconnected to improve propulsion system efficiency. While this may be true for all types of vehicles, disconnecting an axle may be particularly useful in the context of an electric vehicle, in which range of the vehicle may be relatively more important. In the case of a vehicle propulsion system with a single-motor e-axle, i.e., where an electric motor is driving a pair of wheels on a single axle, when disconnection of the axle is desired the motor can be disconnected through a use of a differential with a disconnect mechanism. In some examples, the output gear may be disengaged from internal components of the differential. Accordingly, the motor and output gear of the axle may be slowed or stopped, while internal components of the differential are spun by the wheels of the axle. The moving internal components of the differential generally require lubrication in the disconnected state, whereas the output gear/casing remains stationary. Generally, a lubrication level is maintained within the differential to ensure adequate lubrication. A compromise must typically be struck between lubrication and driveline efficiency. More specifically, to the extent a higher lubrication level is maintained within the differential, moving internal components of the differential are relatively more lubricated, but driveline efficiency is reduced. That is, a greater level of lubrication within the differential necessarily entails higher drag upon the moving internal components of the differential which is applied to the wheels of the axle.

The solutions described in detail herein generally increase the degree to which moving internal components of a differential are lubricated by a given amount of lubrication. Accordingly, lubrication levels may generally be reduced relative to previous approaches, thereby increasing driveline efficiency of the axle while ensuring adequate lubrication of moving components of the differential while in a disconnected state. Power loss associated with the axle may accordingly be reduced relative to previous approaches.

Generally, example approaches herein may employ a position sensor which can determine the tangential or rotational position of a differential casing. The casing may be provided with a casing aperture, which allows an oil jet to supply lubricant from outside the casing to moving components of the differential inside the casing. The position sensor may allow the casing aperture to be aligned with the oil jet, which has a stationary rotational position relative to the differential. For example, the motor may be used to turn the casing to bring the casing aperture into alignment with the location of the oil jet, permitting the oil jet to reach the moving internal components of the differential when the driveline is in a disconnected state.

Example position sensors may be any that is capable of monitoring the tangential position of the differential casing or output gear (to the extent the output gear is fixed to the differential casing). Merely by way of examples, an incremental encoder, a Hall effect sensor, a resolver, or the like may be employed. In some examples, position of the differential casing may be monitored or sensed via a connected rotating component having a rotational position can be expressed as a function of the output gear's position. Merely as one example, a resolver of a motor connected to the casing may measure angular position of a motor rotor, and thereby determine angular position of the differential casing. The position sensor may continuously monitor position of the casing aperture, at least relative to the oil jet. Once a signal to disengage is received, a control logic may use the position sensor or encoder to ensure alignment of the casing aperture and the oil jet, with the speed of output gear being zero. To the extent the casing aperture is misaligned with the oil jet, the motor associated with the axle may be used to rotate the casing to the extent needed to align the casing aperture with the oil jet.

Turning now toFIGS.1,2A,2B, and3, an example differential assembly100is illustrated. Referring initially toFIG.1, the differential assembly100generally includes a differential casing101, which includes an output gear101′ or ring gear structure fixed for rotation with the casing101. Merely by way of example, the output gear101′ may be secured to an outer surface of the casing101, or formed in an outer surface of the casing101. The output/ring gear101′ may be driven by a pinion gear (not shown inFIG.1) which is driven by a vehicle powertrain, e.g., an electric motor or the like. The output gear101′ and casing101may be encased in an outer housing (not shown inFIG.1). The casing101generally provides an enclosure130for a plurality of interfacing components that are part of differential assembly100. For example, the interfacing components may include at least a spindle104that is rotatably supported in the casing101at opposing ends thereof. As will be discussed further below, the spindle104may be selectively disconnected from the casing101, such that the spindle104may rotate freely with respect to the casing101. The spindle104turns a pair of side gears106by way of differential gears105at the ends of the spindle104. The side gears106each drive respective axle shafts or side shafts107. The pinion gear may be positioned to translate rotational motion from a powertrain, e.g., an electric motor, transmission, or the like to the casing101. The side gears106may ultimately drive the axle shafts107in response to the driving of the output gear101′/casing101, while permitting relative differences in speed between the two axle shafts107, as may be needed for a vehicle turning or otherwise when different speeds of wheels corresponding to the axle shafts107, respectively, are needed.

InFIG.1, the differential100is illustrated in a connected state, i.e., where the output gear101′/casing101may transmit torque from a motor (not shown) to the axle shafts107. In this connected state, torque flows from the motor to the axle shafts107from the casing101as indicated by the arrows inFIG.1, and now described in further detail. The differential100may have a disconnect device135, e.g., that is generally configured to selectively engage and disengage torque transmission from the output gear101′ to the axle shafts107. In the example illustrated, the disconnect device includes a laterally shifting collar102, which shifts in a lateral direction with respect to the output gear101′ and/or in a direction parallel to an axis of rotation of the output gear101′. The output gear101′ may have an internal spline113which is engaged with an external spline114of the laterally shifting collar102. The shifting collar102may define an internal spline115that may be enmeshed with an external spline116of a gear nest103. The gear nest103may include a bore that surrounds the spindle104. The spindle104may turn the side gears106by way of differential gears105disposed at either ends of the spindle104. The side gears106may have an internal spline117that is enmeshed with an external spline118of the axle shafts107. Accordingly, torque may be transmitted from the casing101to the axle shafts107, allowing the motor (not shown) to provide power to wheels (not shown) associated with the axle shafts107.

The differential100may be an open differential, i.e., such that a differential speed is permitted between the side gears106, resulting in rotation of the differential gears105. A wave spring108is illustrated which applies an axial force to the shifting collar102, maintaining the collar102in an axial position such that the internal splines115of the shifting collar102remain engaged with the external splines116of the gear nest103.

A casing aperture109is present, which is defined by the casing101and thus may rotate with the casing101. The casing aperture109may be a relatively small window, such that the casing101maintains a level of lubricant within the casing101. An oil jet (not shown inFIG.1) may be directed toward the casing101, such that as the casing aperture109passes through as the casing101rotates, oil or lubricant is directed to the interior components of the differential100, e.g., the side gears106, the spindle104, differential gears105, etc. Any shape or configuration of the casing aperture109may be employed that is convenient. Merely by way of example, the aperture109may form a generally cylindrical through-hole that extends from outside the casing101to an internal region of the differential100, e.g., including the side gears106, the differential gears105, the spindle104, and the gear nest103.

Turning now toFIG.2A, the differential100is illustrated in a disconnected state, i.e., where the casing101and output gear101′ may be slowed or stopped, while the side gears106and axle shafts107are permitted to rotate, e.g., due to rotation of their associated wheels (not shown). In this state, the side gears106may be driven by the rotation of axle shafts107, but the casing101may remain stationary with respect to the differential assembly100. More specifically, the external spline118of the half shafts107turns the internal splines117of the side gears106. The side gears106turn the differential gears105, causing rotation of the spindle104and the gear nest103. However, the gear nest103is disengaged from the casing101, as the disconnect device135has been adjusted such that the differential100is disconnected. In the example illustrated, the shifting collar102has been laterally displaced (against the force of the wave spring108) such that the internal splines115of the shifting collar102have been disengaged from the external splines116of the gear nest103. As a result, the gear nest103rotates within the casing101, and torque is not transmitted from the gear nest103to the collar102(or to the casing101, or to the output gear101′). Accordingly, the motor (not shown) associated with the differential100may be deactivated or stopped, e.g., to reduce consumption of electrical power. The motor (not shown) may, in this disconnected state, still turn the casing101to bring the casing aperture109into alignment with an oil jet110. In one example, a sensor111detects that a radial locator112is positioned such that the casing aperture109is aligned with the oil jet110. The sensor111may determine a rotational position of the casing101and/or output gear101′ based upon a proximity of the locator112to the sensor111. For example, the sensor111may be an incremental encoder configured to read the locator112to determine a rotational position of the casing101and/or aperture109. In another example, the sensor111is a Hall effect sensor configured to determine the position of the casing101and/or aperture109based upon a presence or absence of a magnetic field of the locator112. In some examples, position of the casing101and/or the aperture109may be monitored or sensed via a connected rotating component having a rotational position that can be expressed as a function of a position of the casing101or output gear101′. Merely as one example, an electric motor (not shown) supplying torque to the output gear101′/casing101may measure angular position of an output or rotor of the motor using a resolver. As the output gear101′/casing101has a rotational relationship with the motor, e.g., via gear(s) driven by the motor, which in turn drive the output gear101′/casing101, an angular position of the casing101and/or aperture109may be determined based upon the known rotational position of the rotor of the motor. Accordingly, the casing101may be positioned rotationally such that the casing101does not obstruct the oil jet110, which may freely direct lubricant to the moving components of the differential100, e.g., the ends of the axle shafts107, the side gears106, the differential gears105, spindle104, and the gear nest103.

Referring now toFIG.2B, the differential100is again illustrated in the disconnected state as withFIG.2A. However, inFIG.2Bthe casing101is relatively rotated such that the casing aperture109(not shown inFIG.2B) is not aligned with the oil jet110. As a result, the oil jet110is at least partially blocked with respect to directing lubrication to the internal components of the differential assembly100, e.g., the ends of the axle shafts107, the side gears106, the differential gears105, spindle104, and the gear nest103. As will be discussed further below, in some example approaches the misalignment of the casing aperture109with the oil jet110may be detected, e.g., based upon the position sensor111, and the motor may be used to drive the output gear101′ and/or casing101to bring the casing aperture109back into alignment with the oil jet110(e.g., as illustrated inFIG.2A).

Turning now toFIG.3, the differential100is illustrated with the spindle104, differential gears105, and side gears106each positioned within casing101. As illustrated, in some examples a lower edge of each differential gear105is positioned such that it rotates through a volume of lubricant119having an upper surface120. However, any other lubrication level may be employed that is convenient. In contrast to previous approaches, the amount of lubricant119required for example illustrations herein is relatively reduced, with the upper surface120positioned relatively lower within the differential100compared to these previous approaches, thereby reducing frictional losses of the differential100during a disconnected state of the differential. Moreover, moving internal components of the differential100may still receive sufficient lubrication due to the enhanced circulation of lubricant by way of the oil jet110through the casing aperture109(seeFIG.2A).

As mentioned above regarding each of the example approaches described herein, lower lubrication levels/amounts in a differential may be employed as a result of the enhanced circulation of lubrication to moving differential components. Example differential assemblies may therefore achieve reductions in frictional losses compared with previous approaches. While reductions in frictional losses will vary based upon operating factors and conditions such as oil type, viscosity, operating temperatures, gear size(s), and/or operating speed, example approaches are estimated to achieve a power loss reduction of three percent (3%).

FIG.4shows a block diagram of illustrative electric vehicle400having a control system for controlling one or more drive units and differential assemblies100, in accordance with some embodiments of the present disclosure. While examples herein are described in the context of the electric vehicle400, it should be understood that the various example illustrations herein may be employed in any other type of vehicle without limitation. Merely as examples, in other examples the vehicle400may be powered exclusively by an internal-combustion (IC) engine vehicle, or may have a hybrid powertrain including one or more electric motors in addition to an IC engine. Electric vehicle400includes battery pack430, electric vehicle subsystems410, suspension, and wheels. Electrical vehicle subsystems410includes, for example, rear drive unit412, front drive unit414, control circuitry416, auxiliary systems418, input interface420, and any other suitable corresponding equipment. Electric vehicle400includes power transfer mechanism450(e.g., a gearbox, pulley system, or other mechanism for transferring shaft work including a differential assembly100) corresponding to one drive axis (e.g., rear drive axis) and power transfer mechanism460corresponding to another drive axis (e.g., front drive axis). Vehicle400may include differential assembly100ofFIGS.1,2A,2B, and3as part of either or both of power transfer mechanisms450and460. Vehicle subsystems410may be used to, for example, monitor operation (e.g., sensor signals) of vehicle400, control actuators (e.g., differential actuators or oil jet actuators) of any of the illustrative arrangements and drive systems ofFIG.1-3, or otherwise manage operation of vehicle400. To illustrate, each of power transfer mechanisms450and460may include a differential100and vehicle subsystems410can be used to control the connected/disconnected state of each differential100, control the rotational position of each casing101to align a respective oil jet110with a respective casing aperture109in the disconnected state, and control each oil jet110to provide lubrication through a respective aperture109to a respective internal region130of the differential assembly100.

In some embodiments, control circuitry416may include processing equipment, memory, power management components, any other suitable components for controlling one or more drive unit (e.g., front drive unit414and rear drive unit412), or any combination thereof. For example, control circuitry416may control current flow (e.g., amount of current and current direction) to phases of an electric motor of one or more drive units (e.g., using electric power as stored in battery pack430. In a further example, control circuitry416may control differential operation (e.g., using an electromagnetically-actuated differential) in a single or dual drive unit. In some embodiments, control circuitry416is configured to actuate and de-actuate a differential actuator. For example, control circuitry may provide control signals (e.g., communications, electric power, or both) to (i) one or more differential actuators of power transfer mechanism450,460, or both, or (ii) one or more oil jet actuators of power transfer mechanisms450,460, or both, or (iii) a combination thereof. In a further example, the control signals may be binary (e.g., on/off application of a DC voltage), analog (e.g., the control signal may be proportional based on a voltage range, pulse-width modulation, or pulse-density modulation), oscillatory (e.g., and AC signal or other oscillating signal), any other suitable waveform or shape (e.g., square wave, sawtooth wave, triangular wave, rectified sinusoidal wave), or any combination thereof. In some embodiments, actuators are spring-loaded or otherwise biased in an engaged or disengaged state, and application of electrical power, hydraulic power, or pneumatic power from vehicle subsystem410causes a change in state (e.g., engaged to disengaged, or disengaged to engaged).

In some embodiments, control circuitry416may include one or more sensors, one or more sensor interfaces (e.g., for sensors that are included as part of a drive unit), corresponding wiring, corresponding signal conditioning components, any other suitable components for sensing a state of a drive unit, or any combination thereof. For example, as illustrated in the example inFIG.4, control circuitry416may include sensor interface(s) for communicating with position sensor(s) included in the power transfer mechanism450and/or460(e.g., for each differential casing). The sensor(s) of the power transfer mechanisms450,460may be a position sensor, although in some examples a speed sensor (e.g., a rotary encoder), a current sensor, a voltage sensor, a temperature sensor, any other suitable sensor, or any combination thereof may be provided. In some embodiments, control circuitry416may be implemented by a central controller, a plurality of distributed control systems, an embedded system, or any combination thereof. For example, control circuitry416may be at least partially implemented by an electronic control unit (ECU). In a further example, the electric vehicle may include a power electronics system that is controlled by the ECU and is configured to manage current to one or more electric motors of one or more drive units. Rear drive unit412may be coupled to wheels of the electric vehicle by a half shaft, a constant-velocity joint, one or more suspension/steering components, any other suitable coupling, or any suitable combination thereof. Front drive unit414may be coupled to wheels of the electric vehicle by a half shaft, a constant-velocity joint, one or more suspension/steering components, any other suitable coupling, or any suitable combination thereof. For example, a wheel may be mounted to a hub that is includes a bearing for a half-shaft, wherein the hub is coupled to suspension/steering components that are mounted to the vehicle frame (e.g., wherein the drive units are also mounted to the vehicle frame).

In some embodiments, a drive system may include a first drive unit and optionally a second drive unit, each including a differential assembly. In some embodiments, a drive system, in addition to including a drive unit (e.g., single or dual), may include processing equipment configured to manage motor operation, manage regeneration (e.g., using the motor as a generator), perform any other control function, or any combination thereof. In some embodiments, the drive unit may include at least one sensor (e.g., coupled to a sensor interface of control circuitry) configured to sense wheel slippage and the control circuitry may be further configured to receive a signal from the at least one sensor, detect that wheel slippage is occurring, and activate a differential assembly in response to detecting that wheel slippage is occurring. For example, a sensor may detect shaft speed (e.g., an output shaft speed, as measured by an encoder) or output torque (e.g., an output shaft torque, or a motor torque). In some embodiments, the drive system may include an accelerator pedal configured to indicate a desired speed (e.g., by being depressed by a user), and the processing equipment may receive a signal from the accelerator pedal, determine a speed parameter based on the signal, and activate one or more differential assemblies, one or more motors, or a combination thereof, if the speed parameter is above a threshold. For example, if a user “floors” the accelerator pedal (e.g., more than 50% demand), the control circuitry may activate one or more differential assemblies to provide torque from one or more motors to the wheels. In some embodiments, the control circuitry may activate and deactivate a differential assembly based on road conditions (e.g., icy roads, puddles, high winds), a drive mode (e.g., an off-road mode, a sport mode, or a traction mode), any other suitable criterion, or any combination thereof.

Turning now toFIG.5, an example process500is illustrated for operating a differential, e.g., in a motor vehicle such as an electric vehicle. At block505, process500may operate the differential in a connected state. For example, as noted above torque received from a motor may be transmitted via a differential casing101to a pair of axle shafts107, the axle shafts each having associated wheels. Additionally, the differential casing may at least partially define a lubrication enclosure, e.g., enclosure130, configured to generally contain an amount of lubrication. Further, torque may be transmitted from the differential casing to the axle shafts107via one or more moving internal components disposed within the lubrication enclosure, with each of the side gears configured to receive the torque from the casing while permitting a differential speed between the side gears. Process500may then proceed to block510.

At block510, process500may disconnect the side gears from the casing via a disconnect device, such that the differential is in a disconnected state. For example, as described above inFIG.2B, shifting the collar102allows the casing101to not be turned or driven by the two side gears106, while the side gears106are rotated by their respective vehicle wheel.

Proceeding to block515, process500may sense a rotational position of the casing. For example, a position sensor111having a fixed position on the casing101may be used to determine a radial location of a radial marker112on the casing101. The radial marker112may indicate an alignment of casing aperture109with oil jet110, for example. In another example, a position of a rotor of an electric motor driving the casing101may be related to rotational position of the casing, and thus the position of the casing aperture109may be determined from sensor(s) of the rotor/motor.

Proceeding to block520, process500may query whether the casing and/or output gear is positioned such that the casing aperture109is aligned with oil jet110, e.g., based upon the sensed position at block515. Where process500determines that the casing aperture109is not aligned with the oil jet110, process500may proceed to block525. At block525, while the differential100is in the disconnected state, the casing101may be rotated on the basis of the position sensed at block515. For example, a controller or processor (e.g., control circuitry416ofFIG.4) may be configured to determine, e.g., based upon the position sensed at block515, whether a casing aperture109is aligned with an oil jet110. Alternatively or in addition, the controller may determine a distance the casing/output gear should be rotated to align the casing aperture109with the oil jet110. In an example, the controller may have a processor and a memory in communication with the processor. The memory may include a computer-readable storage medium tangibly embodying instructions, which may cause the controller to implement various processes or steps thereof described herein.

Accordingly, where process500determines that it is necessary to rotate the casing101and/or output gear101′ to improve lubrication of the differential, the casing101/output gear101′ may be rotated while the differential100is in the disconnected state. In an example, the controller/control circuitry416is configured to rotate the casing101and/or output gear101′ when the differential is in the disconnected state in response to the determined rotational position of the casing101and/or output gear101′. For example, the controller/control circuitry416may drive the motor to turn the casing101, bringing the casing aperture109into alignment with the oil jet110that is configured to provide lubrication to the moving internal components via the casing aperture109. Accordingly, the oil jet110is generally not obstructed by the casing101when the casing aperture109is aligned with the oil jet110. Lubrication may therefore be efficiently delivered to the moving internal components, reducing the amount of lubrication needed within the casing101.

The foregoing description includes exemplary embodiments in accordance with the present disclosure. These examples are provided for purposes of illustration only, and not for purposes of limitation. It will be understood that the present disclosure may be implemented in forms different from those explicitly described and depicted herein and that various modifications, optimizations, and variations may be implemented by a person of ordinary skill in the present art, consistent with the following claims.