Methods and systems for a drive axle

Methods and systems are provided for rear axle having a wet bath. In one example, a system comprises a pump configured to spin in a first direction to flow lubricant to a cooler and a second direction to entrain the lubricant with gas.

FIELD

The present description relates generally to lubricant flow in a drive axle sump.

Hypoid gear arrangements may experience high friction levels while providing low noise and backlash. Wet bath arrangements may be used to address lubrication demands and frictional losses experienced by hypoid gear arrangements.

However, the inventors have identified some issues with the approaches described above. For example, wet baths are more expensive and have an increased packaging complexity compared to dry sumps. Additionally, fluid turbulence losses are high when lubricant temperatures are below a lower threshold temperature. Heating of the lubricant may be relatively slow as machinery and axles are used to heat the lubricant.

In one example, the issues described above may be addressed by a system for a pump arranged in a lubricant sump of a rear axle, wherein the lubricant pump is configured to drive in a first direction to direct oil to an oil cooler and a second direction to entrain gas into lubricant in the sump. In this way, a density of the lubricant may be reduced as the machinery, axles, and lubricant warm-up during a cold-start, which may decrease fluid turbulence losses.

As one example, the pump may be activated to operate in the first direction when cooling of the lubricant is desired and in the second direction, opposite the first direction, when reduced density of the lubricant is desired. In this way, the pump may be activated when a temperature of the lubricant is too low or too high while remaining deactivated when the temperature of the lubricant is within a desired range. By doing this, fuel efficiency may be increased.

DETAILED DESCRIPTION

The following description relates to systems and methods for a drive axle. In one example, the drive axle is a rear axle comprising a hypoid gear arrangement, wherein the hypoid gear arrangement is at least partially submerged in a wet bath comprising lubricant. In one example, the lubricant is oil. The drive axle may be used to transfer power from an engine of a vehicle to its wheels, as illustrated inFIG. 1. An example of the drive axle and the hypoid gear arrangement is illustrated inFIG. 2. A pump in conjunction with a cooling circuit for adjusting a temperature and/or density of lubricant in the drive axle is illustrated inFIGS. 3A and 3Bas a one-way drug.FIGS. 4A, 4B, and 4Cillustrate an example of the drive axle comprising a two-way pump which may operate in a first direction and a second direction opposite the first direction. An alternative embodiment of an arrangement for adjusting flow of lubricant within the drive axle is illustrated inFIG. 5. Therein, a valve is arranged downstream of the pump, wherein the valve may be temperature sensitive and configured to adjust flow of the lubricant to either a cooler or to a passage comprising a venturi for aerating the lubricant. A method for adjusting operation of the pump is illustrated inFIG. 6.

FIG. 1shows a schematic depiction of a hybrid vehicle system6that can derive propulsion power from engine system8and/or an on-board energy storage device. An energy conversion device, such as a generator, may be operated to absorb energy from vehicle motion and/or engine operation, and then convert the absorbed energy to an energy form suitable for storage by the energy storage device.

Engine system8may include an engine10having a plurality of cylinders30. Engine10includes an engine intake23and an engine exhaust25. Engine intake23includes an air intake throttle62fluidly coupled to the engine intake manifold44via an intake passage42. Air may enter intake passage42via air filter52. Engine exhaust25includes an exhaust manifold48leading to an exhaust passage35that routes exhaust gas to the atmosphere. Engine exhaust25may include one or more emission control devices70mounted in a close-coupled position or in a far underbody position. The one or more emission control devices may include a three-way catalyst, lean NOx trap, diesel particulate filter, oxidation catalyst, etc. It will be appreciated that other components may be included in the engine such as a variety of valves and sensors, as further elaborated in herein. In some embodiments, wherein engine system8is a boosted engine system, the engine system may further include a boosting device, such as a turbocharger (not shown).

Vehicle system6may further include control system14. Control system14is shown receiving information from a plurality of sensors16(various examples of which are described herein) and sending control signals to a plurality of actuators81(various examples of which are described herein). As one example, sensors16may include exhaust gas sensor126located upstream of the emission control device, temperature sensor128, and pressure sensor129. Other sensors such as additional pressure, temperature, air/fuel ratio, and composition sensors may be coupled to various locations in the vehicle system6. As another example, the actuators may include the throttle62.

Controller12may be configured as a conventional microcomputer including a microprocessor unit, input/output ports, read-only memory, random access memory, keep alive memory, a controller area network (CAN) bus, etc. Controller12may be configured as a powertrain control module (PCM). The controller may be shifted between sleep and wake-up modes for additional energy efficiency. The controller may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines.

In some examples, hybrid vehicle6comprises multiple sources of torque available to one or more vehicle wheels59. In other examples, vehicle6is a conventional vehicle with only an engine, or an electric vehicle with only electric machine(s). In the example shown, vehicle6includes engine10and an electric machine51. Electric machine51may be a motor or a motor/generator. A crankshaft of engine10and electric machine51may be connected via a transmission54to vehicle wheels59when one or more clutches56are engaged. As shown, a drive axle53may be used to transfer power from the transmission54to the wheels59, in one example. The drive axle53is a rear axle, in one example. In the depicted example, a first clutch56is provided between a crankshaft and the electric machine51, and a second clutch56is provided between electric machine51and transmission54. Controller12may send a signal to an actuator of each clutch56to engage or disengage the clutch, so as to connect or disconnect crankshaft from electric machine51and the components connected thereto, and/or connect or disconnect electric machine51from transmission54and the components connected thereto. Transmission54may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various manners including as a parallel, a series, or a series-parallel hybrid vehicle.

Electric machine51receives electrical power from a traction battery61to provide torque to vehicle wheels59. Electric machine51may also be operated as a generator to provide electrical power to charge battery61, for example during a braking operation.

Turning now toFIG. 2, it shows a schematic example of a rear axle200. In one example, the rear axle200may be a non-limiting example of the drive axle53ofFIG. 1. Thus, it will be appreciated that the rear axle200may refer to other types and locations of drive axles. The rear axle200comprises an axle shaft202. The axle shaft202may be a common shaft on which rear wheels of a vehicle are arranged. In one example, the axle shaft202may be fixed to the wheels and rotate with them. In another example, the axle shaft202may be fixed to the vehicle with the wheel rotating about the axle. In one example, additionally or alternatively, the axle shaft202may comprise two halves, a first half coupled to a first rear wheel and a second half coupled to a second rear wheel, wherein the first and second halves may independently rotate the first and second rear wheels.

A differential case210may comprise a differential drive gear212which may receive power from an engine (e.g., engine140ofFIG. 1) via a pinion shaft220and a pinion gear222. The pinion gear222and the differential drive gear212may be complementary to one another such that rotation of the pinion gear in a first direction may drive rotation of the differential drive gear212in a second direction, wherein the second direction rotates about a second axis perpendicular to a first axis about which the first direction rotates.

In one example, the pinion gear222and the differential drive gear212are in a hypoid gear arrangement. Therein, the pinion gear222may be offset from a center of the differential drive gear222, along a large diameter shaft. Additionally, the gears may be beveled and spiraled, with a main variance such that mating gear axes do not intersect. Teeth on the gears may be helical and a pitch surface may be a hyperboloid. The hypoid gear of the present disclosure may comprise an arrangement known to those of ordinary skill in the art.

As the differential drive gear212rotates, it may rotate a pair of differential pinion gears214arranged on opposite sides of the differential drive gear. A first differential pinion gear of the pair of differential pinion gears may be configured to rotate a first differential side gear216, which may result in motion (e.g., rotation) of a first half of the axle shaft202. A second differential pinion gear of the pair of differential pinion gears may be configured to rotate a second differential side gear, which may result in rotation of a second half of the axle shaft202. As described above, rotation of the axle shaft202may result in rotation of the rear wheels of the vehicle.

Turning now toFIG. 3A, it shows an embodiment300of a cross-section of the rear axle200ofFIG. 2taken along a direction parallel to the pinion shaft220. As such, components previously introduced may be similarly numbered in this figure and in subsequent figures.

In the example ofFIG. 3A, the embodiment300of the rear axle200comprises a pump320configured to direct lubricant310to a cooler330. In the example ofFIG. 3A, the pump320is a unidirectional pump configured to flow lubricant and/or air in one direction. The pump320is submerged within the lubricant310. In one example, the pump320is completely submerged such that an entirety of the pump320is arranged below a top level312of the lubricant310. The lubricant310and the pump320are arranged within the housing210and a cover302of the rear axle200, wherein the housing210and the cover302comprise an interior space in which the pinion220, the differential drive gear212, and other portions of the rear axle200are arranged (e.g., pinion gears). A portion of the differential drive gear212may rotate through the lubricant310, which may enhance performance of the differential drive gear212.

However, as described above, during cold starts, a density of the lubricant may be relatively high compared to its density outside of cold starts where the lubricant is hotter. The increased lubricant density during the cold start may introduce a drag onto the differential ring gear212, resulting in power losses and decreased fuel efficiency. As such, the pump320along with other components may be used to decrease the lubricant density during the cold-start.

For example, when a cold-start is occurring and a sensed and/or an estimated temperature of the lubricant310in the interior space (e.g., a sump) of the housing210and cover302is below a threshold temperature, then it may be determined that a density of the lubricant is relatively high. As such, the pump320may be activated and forcibly entrain gas314with the lubricant as the lubricant is pumped out of the sump, to the cooler330, and back to the sump. In this way, the interior space may be filled with gears, lubricant, and the gas (e.g., helium). In one example, the gas314is helium. Additionally or alternatively, the gas314is air, a mixture of air and helium, or the like. Additionally or alternatively, the gas314may be a gas with a density lower than or equal to a density of air. In one example, the gas314may comprise methane (compressed natural gas) mixed with the air and/or helium. It will be appreciated that during the cold-start, the temperature of the lubricant310may be lower than a temperature of the cooler330such that cooling does not take place at the cooler330as the lubricant passes therethrough. Additionally or alternatively, the lubricant310may comprise emulsifier additive, such as a surfactant.

The pump320comprises a vent322with a valve324. The vent322may extend from the pump320to a head space where the gas314is arranged. Said another way, the vent322extends above the top level312of the lubricant310such that the vent322may draw the gas314. The valve324may open in response to the pump320being activated, in one example, wherein gas flows through the vent322and entrains with lubricant in the pump320before flowing to the cooler330. As such, the valve324may be a check valve.

In one example, additionally or alternatively, the valve324may be a solenoid valve configured to actuate in response to a signal from a controller (e.g., controller12ofFIG. 1). The solenoid valve may allow a cooling to occur without entraining air with the lubricant. When energized, the valve324may be opened and the lubricant may be entrained with gas and then flow through the cooler330. While this may slow a warm-up of the lubricant, the emulsification may continue following deactivation of the pump320, which may result in reduced emissions.

In one example, the pump320may comprise two settings, a first setting where lubricant is directed through the pump320via an inlet321and to the cooler330without entraining gas with the lubricant. As such, a rate of the pump (e.g., vacuum generated) may be insufficient to open the check valve324, thereby blocking gas from entraining with the lubricant when the pump is activated to the first setting. The pump320may comprise a second setting, wherein lubricant is directed through the pump320and to the cooler330while further allowing gas to enter the pump320through the check valve324and vent322. As such, a vacuum generated by the pump320may command the check valve324open during the second setting and allow gas314to enter the vent322and entrain with lubricant as the lubricant is directed to the cooler via the pump320. The rate during the second setting may be sufficient to open the check valve324and allow gas to flow therethrough, wherein the gas is entrained with the lubricant and decreases its density, thereby decreasing a drag experienced by the differential drive gear212. As illustrated, lubricant flow is illustrated via a black head arrow and gas flow is illustrated via a white head arrow. Thus, during both setting of the pump, lubricant is direct to the cooler, however, during the first setting, the pump does not entrain gas with the lubricant while gas is entrained with the lubricant during the second setting. It will be appreciated that during the second setting a temperature of the cooler may not be sufficient to cool the lubricant, which may be due to lubricant temperature being low. A lubricant temperature may be determined based on feedback from a temperature sensor342. Feedback from the temperature sensor may adjust valve position and pump operation as will be described herein.

Turning toFIG. 3B, it shows an embodiment350, which is substantially identical to the first embodiment300, except that a release passage352and a three-way valve354are arranged in the first embodiment. In one example, the three-way valve354may be moved to a first position in response to the valve324being commanded to an open position. As such, when gas is mixed with the lubricant, the three-way valve354may be moved to the first position so that lubricant does not flow to the cooler330. As such, the lubricant may be heated more rapidly during a cold-start in the embodiment350compared to the first embodiment300.

When the valve324is closed and cooling is desired, the three-way valve354may be moved to a second position, thereby allowing lubricant to flow to the cooler330. In one example, the three-way valve354may be a temperature controlled valve, such as a wax thermostatic valve. In one example, the valve is configured to move to the first position in response to a temperature being less than a lower temperature threshold and to the second position in response to the temperature being greater than an upper temperature threshold. The lower temperature threshold may be equal to 60° C. and the upper temperature threshold may be equal to 120° C. Operation of the valve may be in response to feedback from the temperature sensor342. Additionally or alternatively, the valve324may be a wax thermostatic valve configured to open in response to a temperature falling below the lower temperature threshold while remaining closed in response to temperatures greater than or equal to the lower temperature. By utilizing wax thermostatic valves, the embodiments300and350may only include a single-direction electrical motor for the pump320, thereby decreasing a cost and complexity of the rear axle200.

Turning now toFIG. 4A, it shows a second embodiment400for a pump420configured to improve fuel economy at low temperatures of the rear axle200while being used in conjunction with a cooling circuit for a high temperature operation.

In the example ofFIG. 4A, the pump420is arranged above the top level312of the lubricant310such that the pump420is exposed to the gas314. The lubricant inlet421extends from the pump420and into a portion of the lubricant310below the top level312. The pump420further comprises an outlet422for directing lubricant to the cooler330and back to the rear axle200, as described above. The pump420additionally comprises a gas inlet424for entraining gas with lubricant based on an operation of the pump420. The entraining may include an aeration of the lubricant or bubbling another gas (e.g., helium) into the lubricant such that the gas may dissolve in or be trapped in the lubricant.

Lubricant flow is illustrated via black head arrows and gas flow is illustrated via white head arrows. When the pump is commanded to operate in a first condition, lubricant is drawn through the lubricant inlet421, through the outlet422, to the cooler330, and returned to the sump of the rear axle200. The first condition may be selected in response to a temperature of the oil exceeding an upper temperature. In one example, the upper temperature may correspond to an upper threshold temperature of the lubricant where its density is too low to provide a desired amount of lubrication to the differential drive gear212. Additionally or alternatively, the upper temperature may correspond to a boiling point of the lubricant, in one example. As such, the first condition may allow the lubricant to be cooled via the cooler330such that a desired temperature range of the lubricant is maintained without entraining gas (e.g., helium, air, carbon dioxide, etc.) into the lubricant.

When the pump is commanded to operate in a second condition, gas is drawn through the gas inlet424, through the lubricant inlet421, and mixed into the lubricant310. The second condition may be selected in response to the temperature of the lubricant falling below a lower temperature. In one example, the lower temperature may correspond to a lower threshold temperature of the lubricant where its density is too high and provides a drag resistance to the differential drive gear212. The lower temperature may occur during an engine cold-start, in one example. As such, during the second condition, only gas is drawn through the pump420, and lubricant is not drawn through the pump420and delivered to the cooler330. In this way, the gas is mixed into the lubricant310via reversing a flow of the pump420to direct gas from the head space of the rear axle200to the lubricant310in the sump.

Turning now toFIG. 4B, it shows an embodiment450of the rear axle200wherein the two-directional pump420is completely submerged in the lubricant310. The pump420may operate in a first direction, where lubricant flows in a direction indicated by black head arrows. As such, lubricant flows through lubricant inlet421, through the pump420, and to the cooler330. To reach the cooler330, a cooler check valve456moves to an open position, wherein the cooler check valve456may be moved to an open position in response to a lubricant temperature exceeding the upper threshold temperature.

The pump420may operate in a second direction, opposite the first direction, in response to a lubricant temperature falling below the lower threshold temperature, which may be sensed by the temperature sensor342. When the pump operates in the second direction, lubricant is drawn through an emulsification inlet460comprising a valve462. The valve462may be commanded open in response to a suction from the pump420or in response to a temperature of the lubricant being less than the lower threshold temperature. Gas may enter the gas inlet452and flow through a valve454, which may be opened in response to a low pressure generated by the pump420. The lubricant and gas may mix at or adjacent to the pump420before exiting through the lubricant inlet421and mixing with lubricant in the sump.

Turning now toFIG. 4C, it shows an embodiment475of the rear axle comprising the bi-directional pump420. The embodiment475is substantially identical to the embodiment450, except that the embodiment475comprises electrically actuated valves, including a first valve482and a second valve484. The first valve482may be a two-way valve arranged in the gas inlet452which is signaled to open in response to a sensed lubricant temperature being less than the lower threshold temperature, thereby indicating a density of the lubricant is relatively high and a cold-start is occurring. The second valve484may be an electronically controlled three-way valve arranged downstream of the pump420at an interface between the emulsification inlet460and the outlet422. The second valve484may be moved to a first position when the pump operates in the first direction to allow lubricant to flow to the cooler330. The second valve484may be moved to a second position when the pump420operates in the second direction, which allows lubricant to enter through the emulsification inlet460, flow through the second valve484to the pump420, and through the lubricant inlet421back to the sump. When lubricant enters the emulsification inlet460, the first valve482is also commanded open so that gas may entrain with the lubricant before it returns to the sump.

In each of the examples shown inFIGS. 3A to 4Cmay comprise where the gas entrainment is arranged at a location where a suction of the pump is sufficient to draw gas through a gas inlet. As such, it may be desired to arrange the gas inlet as close as possible to the pump.

Turning now toFIG. 5, it shows an alternative embodiment500of an entraining/cooling arrangement502, which comprises valve510for adjusting a lubricant flow through the entraining/cooling arrangement502. Due to the inclusion of the valve510, a complexity of the pump520may be reduced and a manufacturing cost may therefore also be reduced. Solid line arrows indicate a flow of lubricant when the valve510is in a first position and dashed line arrows indicate a flow of lubricant when the valve510is in a second position. Lubricant flow is illustrated via black head arrows and gas flow is illustrated via white head arrows.

The pump520may draw lubricant through a first passage512, wherein lubricant flows through the first passage and to the valve510. In one example, the valve510is temperature regulated, such that a position of the valve may switch in response to a sensed temperature of the lubricant. In one example, if the lubricant temperature is greater than or equal to a lower temperature, then the valve may be switched to a first position. In the first position, lubricant flows from the first passage to a second passage514, wherein the second passage guides the lubricant to the cooler530. Once the lubricant flows through the cooler530, it is returned to a sump of a rear axle from where the lubricant was drawn.

If the lubricant temperature is less than the lower temperature, then the valve may be switched to a second position. In one example, the valve comprises a phase-changing material, such as wax, that is set to phase-change at the lower temperature. Thus, if the lubricant flowing through the valve510is less than the lower temperature, the wax may remain solid and the second position may be maintained. In the second position, the valve510may fluidly couple the first passage512to a third passage516. A venturi518may be arranged within the third passage516with a vent519fluidly coupled to a venturi throat, wherein the venturi throat corresponds to a narrowest portion of the venturi518. As lubricant flows through the venturi518, a vacuum generated therein may pull gas through the vent519. As such, gas may mix with the lubricant in the venturi518before exiting the third passage516and returning to the sump of the rear axle from which the lubricant was drawn.

In this way, the entraining/cooling arrangement502may be configured to either cool or entrain gas with the lubricant based on its temperature. In one example, the valve510of the entraining/cooling arrangement502may switch without electrical controls to direct the lubricant to be either cooled or aerated. Additionally or alternatively, the pump520may be integrally formed with the cover of the rear axle. Additionally or alternatively, the valve510may be electronically controlled, wherein the temperature of the lubricant may be sensed via a sensor or estimated via models based on data stored in a multi-input look-up table, wherein the inputs include vehicle speed, ambient temperature, and powertrain power (e.g., load). Positive displacement via the pump520may be powered via a gear or a vane. In one example, the pump520is solenoid activated.

Turning now toFIG. 6, it shows a method600for adjusting an operation of a pump arranged in a sump of a rear axle. Instructions for carrying out method600may be executed by a controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference toFIG. 1. The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below.

The method600begins at602, which includes determining current operating conditions. Current operating conditions may include determining, estimating, and/or measuring one or more of an engine temperature, engine speed, throttle position, vehicle speed, engine load, powertrain power, and air/fuel ratio. Additionally or alternatively, the current operating conditions may include determining an ambient temperature.

The method600proceeds to603, which includes estimating a lubricant temperature. The lubricant temperature may be estimated based on an algorithm which factors a combination of the powertrain power, ambient temperature, and vehicle speed. In one embodiment, as the ambient temperature, the powertrain power, and/or vehicle speed increase, the lubricant temperature may also increase.

The method600proceeds to604, which includes determining if the lubricant temperature is less than a lower threshold temperature. In one example, the lower threshold temperature may be based on a cold-start temperature of the vehicle. Additionally or alternatively, in one example, the lower threshold temperature is equal to a current ambient temperature. If the lubricant temperature is less than the lower threshold temperature, then the method600proceeds to606, which includes commanding the pump to a reverse operation. In one example, the pump (e.g., pump420ofFIG. 4) may be commanded to pull in a reverse direction, such that gas is drawn through a gas inlet. The method600proceeds to608, which includes entraining gas with the lubricant. The gas drawn through the gas inlet may be mixed with lubricant in the sump of a rear axle, resulting in gas mixing with lubricant arranged in the sump. By doing this, a density of the lubricant is reduced while its temperature is below the lower threshold temperature. In one example, the pump does not draw lubricant and/or flow lubricant to the cooler.

If the lubricant temperature is not less than the lower threshold temperature, then the method600proceeds to610, which includes determining if the lubricant temperature is greater than an upper threshold temperature. If the lubricant temperature is greater than the upper threshold temperature, then the method600proceeds to612to command the pump to a forward operation. The forward operation of the pump may result in lubricant flowing through a lubricant inlet, through the pump, and to a cooler. The method600proceeds to614, which includes cooling lubricant in the cooler. Once the lubricant is cooled via the cooler, the lubricant is returned to the sump of the rear axle. As such, when the pump is run in the forward direction, the lubricant may not be entrained with gas.

If the lubricant temperature is not greater than the upper threshold temperature, then the lubricant temperature may be equal to or between the lower threshold temperature and the upper threshold temperature. As such, entraining gas with and cooling of the lubricant may not be desired. As such, the method600proceeds to616, which includes maintaining current operating parameters and do not active the pump. As such, the lubricant may not be directed out of the sump and gas may not be directed to mix with the lubricant.

In this way, fuel economy may be enhanced via an arrangement configured to aerate or cool lubricant arranged in a sump of a rear axle. Aeration may occur in response to a lubricant temperature being less than a lower threshold and cooling may occur in response to the lubricant temperature being greater than an upper threshold. The technical effect of entraining the lubricant with gas is to decrease a friction in the rear drive axle at lower lubricant temperatures. By entraining the lubricant with gas during, for example, a cold-start, frictional drag experienced at the rear axle may be decreased, which may decrease emissions during the cold-start via the arrangement, which may have a low-cost of manufacture.

An embodiment of a system, comprises a pump arranged in a lubricant sump of a rear axle, wherein the lubricant pump is configured to drive in a first direction to direct oil to an oil cooler and a second direction to entrain gas with lubricant in the sump.

A first example of the system, further includes where the second direction is opposite the first direction, and wherein the second direction does not flow lubricant through the pump.

A second example of the system, optionally including the first example, further includes where the pump is arranged above a top level of lubricant in the sump, wherein the pump comprises a first passage at least partially submerged in the lubricant, a second passage fluidly coupling the pump to a cooler arranged outside of the rear axle, and a third passage fluidly coupled to a head space above the top level.

A third example of the system, optionally including one or more of the previous examples, further includes where lubricant flows through the first and second passages when the pump is operated in the first direction, wherein the lubricant flows to the cooler and is returned to the rear axle.

A fourth example of the system, optionally including one or more of the previous examples, further includes where gas flows through the third passage and the first passage when the pump is operated in the second direction, wherein gas flows into lubricant arranged in the sump, wherein the gas is helium.

A fifth example of the system, optionally including one or more of the previous examples, further includes where a controller with computer-readable instructions stored on non-transitory memory thereof that when executed enable the controller to operate the pump in the first direction in response to a lubricant temperature exceeding an upper threshold temperature.

A sixth example of the system, optionally including one or more of the previous examples, further includes where the instructions further enable the controller to operate the pump in the second direction in response to a lubricant temperature being less than a lower threshold temperature.

A seventh example of the system, optionally including one or more of the previous examples, further includes where the lower threshold temperature corresponds to a cold-start of an engine included in a vehicle in which the rear axle is arranged.

An eighth example of the system, optionally including one or more of the previous examples, further includes where the instructions further enable the controller to deactivate the pump in response to the lubricant temperature being between or equal to the lower and upper threshold temperatures.

An embodiment of a vehicle arrangement, comprises a rear axle configured to receive power from a powertrain including an engine, the rear axle comprising a hypoid gear arrangement arranged in a sump comprising a lubricant, a pump coupled to the rear axle, wherein the pump is configured to entrain gas with the lubricant by operating in a reverse direction, wherein the pump is configured to flow the lubricant to a cooler arranged outside of the rear axle by operating in a forward direction, and a controller with computer-readable instructions stored on non-transitory memory thereof that when executed enable the controller to operate the pump in the reverse direction when a lubricant temperature is less than a lower threshold temperature and operate the pump in the forward direction when the lubricant temperature is greater than an upper threshold temperature.

A first example of the vehicle arrangement further comprises where the lubricant temperature is based on one or more of an ambient temperature, a vehicle speed, and a powertrain power.

A second example of the vehicle arrangement, optionally including the first example, further includes where the pump is incorporated into a cover of the rear axle.

A third example of the vehicle arrangement, optionally including one or more of the previous examples, further includes where the pump comprises a first passage configured to admit lubricant through the pump in the forward direction or expel gas into the lubricant in the reverse direction, the pump further comprises a second passage configured only to flow lubricant to a cooler arranged outside of the rear axle, the cooler comprising a return passage configured to return lubricant to the sump, wherein the pump further comprises a third passage configured to only admit gas to the pump.

A fourth example of the vehicle arrangement, optionally including one or more of the previous examples, further includes where the first passage is at least partially submerged below a top level of the lubricant in the sump, and wherein the third passage is arranged completely above the top level of the lubricant in the sump.

A fifth example of the vehicle arrangement, optionally including one or more of the previous examples, further includes where the lubricant is oil, and wherein the gas comprises a density less than or equal to a density of air, and wherein the pump is a positive displacement pump.

An embodiment of a method, comprises activating a pump to operate in a first direction to flow lubricant through a first passage, to a second passage, and to a cooler in response to a lubricant temperature exceeding an upper threshold temperature, wherein the pump is arranged in a rear axle and the lubricant is arranged in a sump of the rear axle, activating the pump to operate in a second direction opposite the first direction to flow gas through a third passage, to the first passage, and into the sump to mix with lubricant in response to the lubricant temperature being less than a lower threshold temperature, and deactivating the pump in response to the lubricant temperature being between the upper threshold temperature and the lower threshold temperature.

A first example of the method further includes where the first passage is at least partially submerged in the lubricant arranged in the sump, and wherein the third passage is arranged above a top level of the lubricant arranged in the sump.

A second example of the method, optionally including the first example, further includes where flowing gas through the first passage includes flowing gas in a direction opposite a direction of lubricant flow through the first passage.

A third example of the method, optionally including the one or more of the previous examples, further includes where the lubricant leaving the cooler is returned to the sump.

A third example of the method, optionally including the one or more of the previous examples, further includes where the pump is inside a housing of the rear axle.

In another representation, the engine is an engine of a hybrid vehicle.