Patent ID: 12216084

DETAILED DESCRIPTION

The following description relates to an oil sensor. In one example, the oil sensor is a system for metallic (ferromagnetic) debris detection. The system may include a detection circuit including a first inductor and a second inductor, the second inductor shielded by the first inductor and an external case of the oil sensor. The detection circuit generates an output based on a difference between a first voltage of the first inductor and a second voltage of the second inductor, where the difference indicates a presence of metallic (ferromagnetic) debris within oil. In this way, a presence and quantity of metal debris may be detected in oil without interference from temperature or other parasitic voltage affecting elements. Thus, a level of oil degradation may be determined. Further degradation of oil and/or mechanical elements may be reduced using methods (e.g., beyond the scope of the herein described embodiment) which may be implemented following indication of oil degradation by the oil sensor.

The oil sensor may be implemented in a system which includes an oil-lubricated part. For example, the oil sensor may be implemented in an electric drive system of a vehicle, as schematically depicted inFIG.1. The electric drive system may include an oil circuit and a coolant circuit for cooling and lubrication of components in the system.FIG.2shows an electric drive system with an electric machine and a gearbox, which may be an example of the electric drive system ofFIG.1.FIG.3shows a cross-sectioned interior of the electric drive system ofFIG.2. The electric drive system includes an oil receptacle, such as an oil well or oil tank, which may have an oil sensor positioned at least partially therein, as shown inFIG.4.

The oil sensor may include components for detecting deterioration of oil due to metal debris in the oil, including a first inductor, a second inductor, a magnet, and a circuit board, as shown inFIG.5. The circuit board may include circuitry, shown inFIG.6, which allows for detection of metal debris in the oil based on a voltage difference of the first inductor and the second inductor.FIG.7details a method for detecting metal debris in the oil based on the voltage difference. The method ofFIG.7may generate a voltage which may be used in a method ofFIG.8to determine a quantity of metal debris in the oil and alert a user to a presence and quantity of metal debris in the oil.FIGS.2-5are drawn approximately to scale. However, other relative component dimensions may be used, in other embodiments.

As briefly described above, the oil sensor described herein may be used in systems having lubricated parts, such as mechanical drive systems, electric drive systems, and/or non-vehicle mechanical systems. Herein, the oil sensor is described as being implemented in an electric drive system, however the oil sensor may be implemented in other systems having lubricated parts.FIG.1schematically illustrates an electric vehicle100with an electric drive system102that provides power to and/or is incorporated into an axle assembly104vehicle100. The vehicle100may take a variety of forms in different examples, such as a light, medium, or heavy duty vehicle. Additionally, the electric drive system102may be adapted for use in front and/or rear axles, as well as steerable and non-steerable axles. To generate power, the electric drive system102may include an electric machine106. In some examples, the electric machine106may be an electric motor-generator and may thus include conventional components such as a rotor, a stator, and the like housed within an electric machine housing107for generating mechanical power as well as electric power during a regenerative mode, in some cases. Further, in other examples, the vehicle100may include an additional motive power source, such as an internal combustion engine (ICE) (e.g., a spark and/or compression ignition engine), for providing power to another axle. As such, the electric drive system102may be utilized in an electric vehicle (EV), such as a hybrid electric vehicle (HEV) or a battery electric vehicle (BEV).

In some examples, the electric machine housing107may be coupled (e.g., via bolts) to a housing109of a gearbox108. Further, the electric machine106may provide mechanical power to a differential110via the gearbox108. From the differential110, mechanical power may be transferred to drive wheels112,114by way of axle shafts116,118, respectively, of the axle assembly104. As such, the differential110may distribute torque, received from the electric machine106via the gearbox108, to the drive wheels112,114of the axle shafts116,118, respectively, during certain operating conditions. In some examples, the differential110may be a locking differential, an electronically controlled limited slip differential, or a torque vectoring differential.

The gearbox108may be a single-speed gearbox, where the gearbox operates in one gear ratio. However, other gearbox arrangements have been envisioned such as a multi-speed gearbox that is designed to operate in multiple distinct gear ratios. Further, in one example, the electric machine106, the gearbox108, and the differential110may be incorporated into the axle assembly104, forming an electric axle (e-axle) in the vehicle100. The e-axle, among other functions, for provides motive power to the wheels112,114during operation. Specifically, in the e-axle embodiment, the electric machine and gearbox assembly may be coupled to and/or otherwise supported by an axle housing. In one particular example, the e-axle may be an electric beam axle where a solid piece of material (e.g., a beam, a shaft, and/or a housing extend(s) between the drive wheels). The e-axle may provide a compact arrangement for delivering power directly to the axle. In other examples, however, the electric machine106and the gearbox108may be included in an electric transmission in which the gearbox and/or electric motor are spaced away from the axle. For instance, in the electric transmission example, mechanical components such as a driveshaft, joints (e.g., universal joints), and the like may provide a rotational connection between the electric transmission and the drive axle.

The electric drive system102may further include an oil circuit120for circulating oil (e.g., natural and/or synthetic oil) through the gearbox housing109to lubricate and/or cool various system components. The oil circuit120may include a filter123and an oil pump124that draws oil from an oil reservoir111(e.g., a sump) in the gearbox housing109, via an outlet122, and drives a pressurized oil flow through a delivery line126to an inlet128of the gearbox housing109. As further described inFIGS.2-6, the oil reservoir111may include an oil sensor for detecting deterioration of oil. In some examples, the oil pump124may be provided at an exterior portion of the gearbox housing109. However, in other examples, the oil pump may be included within the housing109. Various distribution components and arrangements (e.g., nozzles, valves, jets, oil passages, and the like) of the oil circuit120may be included within the electric drive system102in order to facilitate routing of the oil within the gearbox housing109and, in one particular example, to a portion of the electric machine housing107. In some case, the oil circuit120may be used for routing oil to various gearbox shafts and gears as well as a rotor shaft bearing of the electric machine, thereby providing an efficient system for effectively using the gearbox oil to cool said bearing.

The electric drive system102may further include a coolant circuit130that circulates coolant (e.g., water and/or glycol) through a water jacket131formed in the electric machine housing107. The coolant circuit130may include a coolant inlet138and a coolant outlet132positioned on (or in) the electric machine housing107. The coolant circuit130may further include a filter133and a pump134that circulates coolant from the coolant outlet132to the coolant inlet138via a coolant delivery line136. From the coolant inlet138, the coolant travels into the water jacket131formed in the electric machine housing107which removes heat from components of the electric machine106. In some examples, the coolant circuit130may further include a heat exchanger (e.g., radiator) which removes heat from the coolant that exits the electric machine housing107by way of the coolant outlet132.

The vehicle100may also include a control system140with a controller141. The controller141may include a processor142and a memory144. The memory may be non-transitory memory and may hold instructions stored therein that when executed by the processor cause the controller141to perform various methods, control techniques, and the like described herein. The processor142may include a microprocessor unit and/or other types of circuits. The memory144may include known data storage mediums such as random access memory, read only memory, keep alive memory, combinations thereof, and the like. The controller141may receive various signals from sensors146positioned in different locations in the vehicle100and electric drive system102. For example, sensors146may include the oil sensor described inFIGS.4-6. The controller141may also send control signals to various actuators148coupled at different locations in the vehicle100and electric drive system102. For instance, the controller141may send command signals to the oil pump124and/or the pump134and, in response, the actuator(s) in the pump(s) may be adjusted to alter the flowrate of the oil and/or coolant delivered therefrom. In other examples, the controller may send control signals to the electric machine106and, responsive to receiving the command signals, the electric machine may be adjusted to alter a rotor speed. The other controllable components in the system may be operated in a similar manner with regard to sensor signals and actuator adjustment.

An axis system150is provided inFIG.1, as well asFIGS.2-3, for reference. The z-axis may be a vertical axis (e.g., parallel to a gravitational axis), the x-axis may be a lateral axis (e.g., horizontal axis), and/or the y-axis may be a longitudinal axis, in one example. However, the axes may have other orientations, in other examples.

FIG.2depicts an example electric system200with an electric drive system202for providing power to an axle assembly204. The electric drive system202may include an electric machine206operatively coupled to a gearbox208and may be included in a vehicle, such as the vehicle100depicted inFIG.1, and may thus share similarities with the electric drive system102. For instance, at least a portion of the components discussed with regard to the drive system102, shown inFIG.1, may be included in the electric drive system202, shown inFIG.2, or vice versa.

The electric machine206may include an electric machine housing207coupled to a gearbox housing209of the gearbox208. In some cases, the electric machine housing207may be coupled to the gearbox housing209via fasteners, such as bolts211, for instance. To elaborate, the gearbox housing209may have an inboard side213, opposite an outboard side215thereof, coupled to an outboard side217of the electric machine housing207, as illustrated inFIG.2. Further, the electric machine housing207may include a coolant outlet242and a coolant inlet248of a coolant circuit (e.g., the coolant circuit130ofFIG.1) for moving coolant through a water jacket formed in the electric machine housing207.

The electric machine206may provide power to a differential210via the gearbox208to provide rotational power to axle shafts216,218(to which drive wheels may be coupled) of the axle assembly204. In one example, the differential210and the axle shafts216,218may be at least partially enclosed within an axle housing205. In some examples, the axle housing205may include a differential cover203attachable thereto, near the differential, which may allow for access to the differential for maintenance, repair, etc. Further, the axle housing205and differential cover203may be designed so as to maintain a reservoir of oil in the vicinity of the differential210, allowing for splash lubrication of components housed therein. The oil may be delivered to the axle housing205from the gearbox housing209(e.g., via an oil circuit similar to the oil circuit120ofFIG.1), which may also have a reservoir of oil collected in a bottom portion thereof. For example, the reservoir of oil in the gearbox housing209may be the oil reservoir111ofFIG.1, with the oil sensor positioned therein, as further described inFIG.4.

The gearbox housing209may include a shaft and gearing arrangement housed therein for providing power to the differential210disposed within the axle housing205. As such, the gearbox housing209may be fixedly mounted to the axle housing by any suitable attachment mechanism (e.g., bolts, brackets, welds, and/or combinations thereof) in a region adjacent to the differential210, generally indicated as250. Further, the electric machine housing207may be coupled to the axle housing205, at a second location generally indicated as252, by similar or other suitable mounting apparatuses. Other mounting arrangements have been envisioned, such as, for instance, where the electric machine housing207is not mounted to the axle housing205but rather suspended from the gearbox housing209in a cantilevered fashion. Such an arrangement, however, may provide less structural support to the electric machine.

The electric machine206and the gearbox208may thus be integrated with the axle assembly204, in some examples, in an e-axle. Further, the axle housing205, the electric machine housing207, and the gearbox housing209may each be made of a metal (e.g., aluminum, steel, combinations thereof, and the like) which may be the same or a different metal for each housing.

FIG.3shows a partial cross-sectional view of the electric drive system202and axle assembly204shown inFIG.2, as defined by a lateral cut taken along dashed line3-3.FIG.3illustrates a portion of the electric drive system202, including the electric machine206and gearbox208. The electric machine206may include a stator300and a rotor302enclosed in a working chamber301of the electric machine housing207.

The electric drive system202may further include an oil circuit303and a coolant circuit305that cool and/or lubricate electric machine and/or gearbox components, which may share similarities with the oil circuit120and the coolant circuit130, respectively, depicted inFIG.1. The electric machine housing207includes a water jacket304formed therein with coolant channels306, which is included in the coolant circuit305. The coolant channels306may receive coolant from upstream components in the coolant circuit305, via an inlet formed in the electric machine housing207, as previously discussed with regard to the coolant circuit130ofFIG.1. The coolant circulating through the water jacket304may function to remove heat from the stator, rotor, and bearings of the electric machine206.

The rotor302is designed to electromagnetically interact with the stator300to provide torque to a gearbox shaft308(e.g., a gearbox input shaft) via a rotor shaft310. The rotor shaft310may be supported for rotation in the electric machine housing207by bearings positioned at outboard and inboard ends thereof. In the frame of reference depicted inFIG.3, the inboard and outboard ends of the rotor shaft are the right and left ends, respectively. In particular, a front rotor shaft bearing312is shown disposed on the rotor shaft310near the outboard end thereof proximal to the gearbox208. In some examples, the rotor shaft bearing312may be a radial bearing, such as a spherical ball bearing. More generally, the rotor shaft bearing312may include an inner race, an outer race, and rolling elements (e.g., rollers or spherical balls). The inner race of the bearing312is in contact with the rotor shaft310and the outer race may be in contact with the electric machine housing207.

The gearbox shaft308may be supported for rotation in the gearbox housing209by a gearbox shaft bearing309. As such, the bearing309is positioned on the gearbox shaft308. In some cases, the bearing309may have a different configuration than the rotor shaft bearing312. For instance, the bearing309may be a thrust bearing, such as a tapered roller bearing. Thus, the design of the bearings309and312may be tailored to withstand the expected loading in the system, thereby increasing the system's longevity. The bearing309generally includes an inner race, an outer race, and rolling elements (e.g., tapered rollers). As such, the inner race is in contact with the gearbox shaft308and the outer race may be in contact with the gearbox housing209.

In one example, as illustrated inFIG.3, the electric machine housing207of the electric machine206may be coupled to the gearbox housing209of the gearbox208by way of bolts211. For instance, an inboard side213of the gearbox may be coupled to the motor housing. Further, the gearbox shaft308may be coupled for rotation with the rotor shaft310, such that a shaft interface314is formed therebetween within the gearbox housing209. Specifically, the shaft interface314is formed between an outboard end315of the rotor shaft310and an inboard end317of the gearbox shaft308. In the frame of reference illustrated inFIG.3, the inboard end of the gearbox shaft is the right end of the shaft and the outboard end is the left end of the shaft.

In some examples, the shaft interface314may be a splined interface. In such an example, each of the rotor shaft310and the gearbox shaft308may have a plurality of splines that extend axially along a portion thereof, at the outboard end315and the inboard end317, respectively. Specifically, in one example, the rotor shaft310may have splines disposed on an exterior surface331at a portion of the outboard end315thereof. The outboard end of the rotor shaft is the rotor shaft's left end in the frame of reference illustrated inFIG.3. The gearbox shaft308may have splines on an interior surface333along a portion of the inboard end317thereof. The splines on the gearbox and rotor shafts axially extend along a length of the corresponding shaft. Additionally, the rotor shaft310and the gearbox shaft308are coaxially disposed and therefore have a common rotational axis316.

In some examples, a housing seal318may be disposed between the electric machine housing207and the gearbox housing209. More specifically, the housing seal318may be disposed at a housing interface320(between the electric machine housing207and the gearbox housing209) in the vicinity of the splined shaft interface314. Further, the housing seal318may form a portion of a boundary of a sealed cavity322. Oil may be introduced into the sealed cavity322through oil passages in the shaft interface314and from the sealed cavity oil flows to the front rotor shaft bearing312. Other boundaries of the sealed cavity322may include a portion of an interior surface of the gearbox housing209and a portion of an interior surface of the electric machine housing207, a portion of an outer surface of the gearbox shaft308, and/or a portion of an outer surface of the rotor shaft310. In one example, the sealed cavity322may be bounded by a rotor shaft seal324positioned on an inboard side of the rotor shaft bearing312. The sealed cavity322may be the oil reservoir111ofFIG.1and have the oil sensor positioned at least partially therein. Details of the sealed cavity322and the oil sensor are expanded upon with reference toFIGS.4-6.

Returning toFIG.3, the gearbox shaft308may have a gear328formed thereon outboard of the bearing309, proximate an outboard end355of the gearbox shaft. A bearing345may be coupled to the outboard end355of the gearbox shaft308. To elaborate, the bearing345may include an outer race that contacts the gearbox housing209and an inner race that is disposed around the gearbox shaft308. Further, in some examples, a cover357may be coupled to the side215of the gearbox housing209at a position corresponding to the outboard end355of the gearbox shaft308, such that an oil chamber359is formed between the cover357and the outboard end of the gearbox shaft. In some cases, this oil chamber359may receive and at least partially retain oil for subsequent routing through the gearbox housing and components. The oil chamber359may be an additional or alternative example of the oil reservoir111ofFIG.1, and have the oil sensor positioned at least partially therein.

As depicted inFIG.3, the gear328may be in meshing engagement with a first gear330which is disposed on a shaft332(e.g., a gearbox output shaft), so that rotational power from the rotor shaft310may be transferred to the gearbox shaft308and then to the shaft332by way of the meshing gears328,330. The shaft332may be supported within the gearbox housing209by a pair of bearings334(e.g., roller bearings, such as cylindrical or spherical roller bearings) positioned on opposing axial ends of the shaft. Further, the shaft332may have a rotational axis336which is parallel to, and offset from, the common rotational axis316of the rotor shaft and gearbox shaft. However, other gearbox configurations have been contemplated. For instance, the shaft332may be omitted from the gearbox and power may be transferred directly from the shaft308to the differential210, shown inFIG.2.

The shaft332may have a second gear338formed thereon and in meshing engagement with an input gear of the differential210ofFIG.2. Thus, rotational power received at the shaft332may be transferred to the input gear of the differential via the second gear338, whereby rotational power may be distributed to the axle shafts216,218of the axle assembly204and eventually to drive wheels (e.g., the wheels112,114ofFIG.1), in some examples. The gearbox housing209may be attached to the axle housing as generally indicated at location250. Further, the electric machine housing207may also be coupled to the axle housing205at a location252, different from location250. In one example, location250may be proximate an inboard side219of the electric machine housing207, opposite the outboard side217of the electric machine housing. Further, a bracket360on the electric machine housing207may be joined to a bracket362on the axle housing205via bolts364, though other suitable fastening arrangements have been contemplated.

The electric drive system described herein provides an efficient architecture for routing oil through a shaft interface between a rotor shaft and a gearbox shaft to cool and lubricate a front rotor shaft bearing disposed within an electric machine housing. When mechanical wear occurs to elements of the electric drive system, metal debris may become suspended in the oil and flow through the lubrication system, which may further degrade elements of the electric drive system. An oil sensor, further described inFIGS.4-6, may be at least partially positioned in an oil reservoir, such as the oil reservoir111ofFIG.1, examples of which may be at least one of the sealed cavity322or the oil chamber359ofFIG.3. The oil sensor may infer a presence of metal debris in the oil and prevent metal debris from circulating with the flow of oil using two inductors with an associated detection circuit, further described inFIGS.4-6.

As previously described, the oil sensor is at least partially positioned in an oil reservoir of a lubricating circuit, such as the oil reservoir111ofFIG.1, which may be at least one of the sealed cavity322or the oil chamber359ofFIG.3.FIG.4shows an embodiment400of an oil reservoir402with an oil sensor408positioned at least partially therein. In the example ofFIG.4, the oil sensor408is positioned in a vertical wall of the oil reservoir402such that a first region408aof the oil sensor408is in an interior of the oil reservoir402and a second region408bof the oil sensor408is in the vertical wall and extends to an exterior of the oil reservoir402.

The oil reservoir402may contain a volume of oil404such that the first region408aof the oil sensor408is submerged in the oil404. The oil404may have metal debris406suspended therein. Metal debris406may be generated as a result of mechanical wear throughout the electric drive system shown inFIGS.1-3. The metal debris406may be generated at a point of mechanical wear, e.g., at a physical interface between metal elements of the electric drive system. The metal debris406may then follow a flow of oil through the lubrication circuit (e.g., ofFIG.1) to the oil reservoir402. As further described inFIG.5, a magnet of the oil sensor408may attract the metal debris406such that it may be held at the oil sensor408and not circulate through the lubrication circuit with the oil404. The oil404may circulate through the lubrication circuit as described inFIGS.1-3.

FIG.5shows a partial cross-sectional view500of the oil sensor408ofFIG.4. The first region408ais shown with an external case502partially cut away, however the external case502may completely surround the oil sensor408, thus forming a barrier between internal elements of the oil sensor408and air and/or oil, and the partial cut is shown for illustration purposes. The external case502may be formed of a material which may shield a second inductor512, herein also referred to as an internal sensing element, from metal debris influences. For example, the external case502may be formed of metal or other non-magnetically inert material. The material forming the external case502may prevent metal debris from accumulating on an external surface (e.g., a surface in contact with oil) of the external case502. At least a portion of the external case502in proximity to the second inductor512may be formed of a material other than plastic, as plastic may not sufficiently shield the second inductor512from an influence of accumulated metal debris. Influence of accumulated metal debris is further described herein.

The second region408bof the external case502may be formed as a screw, which may allow the oil sensor408to be positioned in the wall of the oil reservoir, as shown inFIG.4. The external case502may further include a connector509having a plurality of connectors511therein. The plurality of connectors511may allow the oil sensor408to be in wired or wireless communication with a control system, such as the control system140ofFIG.1, as further described inFIGS.6-7.

Within the external case502, the oil sensor408includes a first inductor504, a first spacer506, a magnet508, a second spacer510, and the second inductor512. The first spacer506and the second spacer510may be formed of plastic or another magnetically inert, nonconductive material. The first inductor504and the second inductor512may have the same structure. For example, the first inductor504and the second inductor512may each be a four-layer spiral. The four-layer spiral may be made of coiled wire, such as copper or other conductive metal wire. The magnet508may be formed by any magnetic material capable of attracting metal or other metallic (e.g., ferromagnetic) debris.

The first inductor504may be positioned at a first end520of the oil sensor408, where the first end is in contact with oil (e.g., the oil404in the oil reservoir402ofFIG.4). In one example, the first inductor504is contained (e.g., separated from the oil) by the external case502. In a second example, a surface of the first inductor504in alignment with the first end520of the external case502is exposed to, and therefore in contact with, the oil.

In a direction towards a second end530of the oil sensor408opposite the first end520, the first spacer506is positioned next to the first inductor504, followed by the magnet508, the second spacer510, and the second inductor512. Each element may be positioned in face sharing contact with the element on either side (e.g., the first spacer506is in face sharing contact with the first inductor504and the magnet508). In another example, there may be a space between each of the elements.

In one example, the first inductor504, the first spacer506, the magnet508, the second spacer510, and the second inductor512have approximately a height522, which is less than a height524of the first region408aof the oil sensor408. Further, the first inductor504, the first spacer506, the magnet508, the second spacer510, and the second inductor512may be positioned with a center point of each element in an approximate middle of the height524. In one example, a first width526of the first inductor504is approximately equal to a second width528of the second inductor512. A third width532of the first spacer506may be greater than, less than, or equal to a fourth width534of the second spacer510. The third width532and the fourth width534may both be greater than the first width526and the second width528. The magnet508may have a fifth width536, which may be greater than the first width526and the second width528, and may be greater than, less than, or equal to the third width532.

The oil sensor408further includes a circuit board514, which may extend into the second region408b. The first inductor504may be coupled to the circuit board514via a first cable516and the second inductor512may be coupled to the circuit board514via a second cable518. For example, the first cable516and the second cable518may be electrical lead connections. The circuit board514may be used to help stimulate a first inductance and a second inductance (e.g., of the first inductor and the second inductor, respectively) and to condition an output signal, as further described inFIG.6.

Briefly, the oil sensor408detects a presence of metal debris in oil (e.g., as shown inFIG.4) by identifying a peak voltage using the first inductor504and the second inductor512. For example, each of the first inductor504and the second inductor512may have an electrical current flowing therethrough. The first inductor504is in contact with the oil and the second inductor512is physically shielded from voltage influences of the oil by the first inductor504and the external case502, and may thus be used as a reference. The current flowing through the first inductor504and the second inductor512generates a magnetic field around each of the first inductor504and the second inductor512.

The magnet508may have a stronger magnetic force than the magnetic fields of the first inductor504and the second inductor512, and may pull metal debris in the oil towards the oil sensor408. This may result in metal debris being held in place proximate to the first inductor504, which may result in more accurate detection of metal debris compared to metal debris suspended in oil throughout the oil reservoir402ofFIG.4.

The magnetic field of the first inductor504may act on the metal debris and result in eddy currents in the metal debris. The eddy currents may result in changes to the magnetic field of the first inductor504. Because the second inductor512is encapsulated in the external case502and placed behind each of the first inductor504, the first spacer506, the magnet508, and the second spacer510(e.g., a distance between the first inductor504and the second end530is larger than a distance between the second end530and any of the first spacer506, the magnet508, the second spacer510, or the second inductor512), the second inductor512may be shielded from the magnetic field resulting from the eddy currents of the metal debris. For example, as the second inductor512is masked by the first inductor504, eddy currents generated by the metal debris may not interfere with the magnetic field of the second inductor512. Further, as the first inductor504and the second inductor512are formed of the same materials, they are similarly influenced by temperature. Due to being in close proximity, the first inductor504and the second inductor512are further similarly influenced by other potential external sources of noise (e.g., vibration due to vehicle movement). As one example, during conditions in which the oil temperature is higher, the conductivity of electrical current through components of the oil sensor408may be decreased. As a result, a strength (e.g., magnitude) of the magnetic fields of the first inductor504and second inductor512may be decreased. During conditions in which the oil temperature is lower, the conductivity of the electrical current through components of the oil sensor408may be increased. As a result, the strength of the magnetic fields of the first inductor504and second inductor512may be increased. In each of the conditions described above, however, because changes to the oil temperature affect the strength of the magnetic fields of the first inductor504and second inductor512equally, variations in the oil temperature do not result in a net difference between the strength of the magnetic field of the first inductor504and the strength of the magnetic field of the second inductor512. Thus, variation due to temperature and other external environmental conditions are filtered from the comparison of differences detected between the first inductor504and the second inductor512, while variations due to the presence of metal debris are detected.

The oil sensor408may determine a quantity of metal debris present in the oil reservoir based on the difference in peak voltage of the first inductor504and the second inductor512. For example, higher overall amounts of metal debris (e.g., higher ratios of the volume of metal debris to the volume of oil) may result in a stronger net magnetic field generated by the entire amount (e.g., entire volume) of metal debris. Each individual piece of metal debris may experience eddy currents which contribute to the net magnetic field (e.g., combined magnetic field) generated by the entire volume of metal debris. Thus, a higher (e.g., stronger) net magnetic field generated by the entire volume of metal debris may be indicative of a higher number of individual pieces of metal debris within the entire volume, while a lower net magnetic field generated by the entire volume of metal debris may be indicative of a lower number of individual pieces of metal debris within the entire volume. Further detail regarding magnetic field generation, eddy current generation, and identification of metal debris presence/quantity is now described with reference toFIGS.6-8.

FIG.6shows a schematic representation of a circuit600of the oil sensor ofFIGS.4-5. The circuit600is an example of a circuit of the circuit board514positioned in the oil sensor408and electronically coupled to elements thereof as previously described and further elaborated on herein. For example, the circuit600is coupled to an external sensing element604and an internal comparison element612. The external sensing element604is the first inductor504and the internal comparison element612is the second inductor512ofFIG.5. The circuit600includes a frequency generator602, a first peak detector606, a second peak detector608, and a comparator610. The circuit600may further include a series resistor to assist in controlling a maximum current which can be driven by the external sensing element604and the internal comparison element612. The comparator610is connected to a control system, such as the control system140ofFIG.1via connectors511ofFIG.5, and is further connected to ground.

The frequency generator602provides alternating electrical current (AC) to each of the external sensing element604and the internal comparison element612, resulting in a magnetic field generated at each of the elements. The frequency generator602may provide a sinusoid wave electrical signal or a square wave electrical signal in some examples. When the external sensing element604and the internal comparison element612have the same structure, as described inFIG.5, power used by the frequency generator602to generate the magnetic fields may be the same for both elements. Power used to generate a magnetic field may be influenced by boundary conditions, which may include temperature (e.g., of the oil), metallic objects in proximity to the magnetic field, influences of other inductors or currents flowing nearby, and so on. Thus, when no metallic objects are in proximity to a magnetic field of the external sensing element, power used to generate magnetic fields for the internal comparison element612and the external sensing element604may be equal. For example, as the internal comparison element612and the external sensing element604have the same structures they are thus affected in the same way by influences such as temperature, thereby compensating for the effect of temperature.

The external sensing element604is coupled to the first peak detector606and the internal comparison element612is coupled to the second peak detector608. Both the external sensing element604and the internal comparison element612are connected to ground. Each of the peak detectors includes a capacitor and a diode, which are used to detect a peak voltage value across the respective element. The first peak detector606includes a first capacitor606aand a first diode606b. The second peak detector608includes a second capacitor608aand a second diode608b. Other peak detector configurations may be implemented which detect voltage peaks of the external sensing element604and the internal comparison element612. The first peak detector606outputs a voltage indicating a peak voltage across the external sensing element604, and the second peak detector608outputs a voltage indicating a peak voltage across the internal comparison element612. An additional capacitor may be added to each peak detector to assist in reducing a power demand used to drive the respective external sensing element604or internal comparison element612. The peak detectors thus detect and maintain the maximum voltage value seen across the respective element.

For example, the first peak detector606may detect a peak voltage of the AC signal provided to the first peak detector606by the external sensing element604. The voltage may peak (e.g., be greater than a baseline voltage, as established by the internal comparison element612) due to interference (e.g., attenuation) of the AC signal by a magnetic field generated by metal debris within the oil, as further described below. The first peak detector606outputs a voltage to the comparator610corresponding to the peak voltage of the external sensing element604.

The voltage of the AC signal provided by the internal comparison element612may not substantially increase when metal debris are present in the oil, as the internal comparison element612is shielded by the external sensing element604and the external case502from effects of the magnetic field generated by the metal debris. The peak voltage detected by the external sensing element604may be equal to the voltage detected by the internal comparison element612when no or negligible metal debris is present in the oil. A difference between the peak voltage detected by the external sensing element604and the peak detected by the internal comparison element612may increase as the amount of metal debris within the oil increases. In other words, during conditions in which the oil includes no metal debris (e.g., no metal debris is within the oil reservoir402ofFIG.4), a peak amplitude (voltage) of the AC signal output by the internal comparison element612may be equal to a peak amplitude of the AC signal output by the external sensing element604. During such conditions, the signal output to the comparator610by the first peak detector606indicating the voltage across the first peak detector606may be equal to the signal output to the comparator610by the second peak detector608indicating the voltage across the second peak detector608. Outputs of the peak detectors are referred to a virtual ground generated at equation 1 by a designated quad-op-amp. In equation 1, V_CGND is a voltage collector (e.g., the external sensing element604or the internal comparison element612) coupled to the virtual ground. V_CC is the voltage common collector.
V_CGND=V_CC/2  (1)

Upon receiving the output signals of each of the first peak detector606and the second peak detector608(which may be referred to herein as inputs of the comparator610), the comparator610may compare the output signals of each of the first peak detector606and the second peak detector608and amplify any difference between the outputs. For example, if the first peak detector606outputs a first voltage, the second peak detector608outputs a second voltage, and a difference between the first voltage and the second voltage is greater than a threshold difference, the comparator610may output a third voltage indicating above threshold difference between the external sensing element604and the internal comparison element612. When the difference is greater than the threshold difference, it may be determined that a presence of metal debris in the oil is not negligible (e.g., may degrade elements of the system). The third voltage may indicate that the voltage of the external sensing element604had changed, which may be due to eddy currents induced by metal debris in the oil. In one example, the threshold difference is 1 mV and may be configurable based on an application of the oil sensor. The threshold difference may be a voltage other than 1 mV and may be configurable based on application of the oil sensor (e.g., depending on the system in which it is integrated) and/or operating conditions.

Additionally or alternatively, the comparator610may output a voltage value equal to the difference of the peaks sensed from the external sensing element604and the internal comparison element612and conditioned by the first peak detector606and the second peak detector608, respectively (e.g., the first voltage and the second voltage). Thus, indication of metal debris presence and quantity is given by the voltage value provided by the comparator610. The oil sensor may not implement a threshold difference and instead outputs the voltage value equal to the difference.

Further, the first voltage and the second voltage may be used to detect a presence and a quantity of metal debris in oil by comparing the third value with a lookup value table. The circuit of the oil sensor may be calibrated by acting on the lookup value table, which may be implemented by a manufacturer and thus allow the oil sensor to operate in different systems (e.g., any system having an oil lubrication device) and under different operating scenarios.

For example, when a conductive element (e.g., metal debris) is in the vicinity of the magnetic field of the external sensing element604, the magnetic field induces circulating currents (e.g., eddy currents) on the conductive element, herein referred to as a target. Eddy currents of the target generate a magnetic field around the target, where a target magnetic field strength is based on a distance of the target from the external sensing element604, and a size and shape of the target. The target magnetic field opposes the magnetic field of the external sensing element604.

The oil sensor may thus measure a change in maximum voltage value across the external sensing element604based on the voltage output by the first peak detector606. As the magnetic field of the internal comparison element612is shielded from eddy current effects, the voltage output by the second peak detector608may be unchanged when metal debris is present in the oil. When the voltages output by the first peak detector606and the second peak detector608are compared at the comparator610, the resulting third voltage may be different than when voltage values are compared when metal debris is absent from the oil. The third voltage output by the comparator610may be used to determine a presence and quantity of metal debris in oil and further may be used to alert a user to a presence of metal debris, as further described inFIG.8.

As briefly described above, other sources of voltage variations may induce parasitic phenomena due to electronic components of the sensor and temperature variation (e.g., varying temperature of the oil and/or of metal components of the oil sensor). Contribution of parasitic phenomena due to electronic components may be reduced by setting the input frequency value (e.g., from the frequency generator602) to a desired value. The desired value may be determined based on a compromise between temperature stability (e.g., the frequency generator602is part of the sensor and thus experiences temperature variations along with other components of the sensor), desired effect of metal debris eddy current on the magnetic field of the external sensing element604relative to the internal comparison element612, and ease of implementation of the frequency generator. The desired value may be different when the oil sensor is implemented in different systems, such as hybrid electric vehicles, electric vehicles, off highway axels, on highway axels, and so on. The oil sensor described herein is targeted to off highway axels.

Voltage variation due to temperature variation may be reduced by positioning of the external sensing element604and the internal comparison element612, as described above. For example, temperature drift may impose variation of the linear output voltage (e.g., output from the external sensing element604and internal comparison element612). Variation of the linear output voltage may be directly proportional to temperature drift. Both the internal comparison element612and the external sensing element604may be influenced in the same way by temperature and other external sources of noise which may result in output variation, due to their placement in close proximity to each other. However, since the internal comparison element612is placed behind the external sensing element604, and other elements of the oil sensor408as described above, the internal comparison element612is masked from effects of a presence of metal debris by the external sensing element604, as described above.

The circuit600may manage outputs of both the external sensing element604and the internal comparison element612to address small differences in inductance due to constructive processes of the inductors or potential temporary imbalance caused by rapid temperature changes. For example, the external sensing element604may be configured to present a higher inductance value or a lower inductance value with respect to the internal comparison element612. Inductance may thus be modeled as a fixed part plus a variable part dependent on a presence of a target, a distance between the target and the external sensing element604, and dimensions of the target. The model may further include a fixed resistance characteristic of the external sensing element604plus a contribution due to the target, and dependent on distance, in series to an ideal inductance (e.g., the internal comparison element612).

FIG.7illustrates a method700for detecting deterioration of oil (e.g., a presence of metal debris) using the oil sensor depicted inFIGS.4-6. The method700may be a high level description of the process conducted by the oil sensor408to detect metal debris in the oil, thus components of the oil sensor described in the method700may refer to components of the oil sensor408.

At702, the method700includes the frequency generator602stimulating current in the first inductor504and the second inductor512. As described above, the first inductor is referred to as the external sensing element604and the second inductor is referred to as the internal comparison element612in the circuit600. Both the first inductor and the second inductor are stimulated with the same current induced by the voltage modulated signal generated by the frequency generator.

At704, the method700includes magnetic fields being induced at each of the first inductor and the second inductor. Current at the first inductor may induce a first magnetic field and current at the second inductor may induce a second magnetic field. A first voltage of the first inductor may be measured by the first peak detector606and a second voltage of the second inductor may be measured by the second peak detector608. Prior to metal debris being in proximity to the oil sensor, for example, prior to metal debris entering the oil reservoir402, the first voltage and the second voltage may be equal. When the first voltage and the second voltage are equal, a third voltage output by the comparator610may indicate to a controller of a system in which the oil sensor is positioned that metal debris is not detected by the oil sensor. For example, the oil sensor may be coupled to the controller141of the vehicle100ofFIG.1, as described inFIGS.4-6.

If metal debris is present in oil and metal debris enters the oil reservoir, at706, the method700includes the magnet508pulling the metal debris towards the first inductor. The first inductor is exposed to oil and thus effects of the metal debris on the first voltage of the first inductor, as further described below, may be detected by the first inductor.

At708, the method700includes the metal debris in proximity to the first inductor generating eddy currents when in proximity to the first magnetic field. For example, each piece of metal debris in proximity to the first magnetic field may generate its own eddy current, and each eddy current may be in contrast to the first magnetic field.

At710, the method700includes the eddy currents of the metal debris interfering with the first magnetic field of the first inductor. For example, as the eddy currents are in contrast with the first magnetic field, generation of the eddy currents may result in a change in the first voltage of the first inductor. As the second inductor is shielded from the effects of the metal debris by the first inductor and by the external case, the second voltage may be unchanged.

At712, the method700may include the first peak detector outputting the first voltage and the second peak detector outputting the second voltage to the comparator. As described above, the first voltage may be a different value compared to when metal debris was not present in the oil, and the second voltage may be unchanged. Thus, the first voltage and the second voltage may be different, unequal values.

At714, the method700includes the comparator outputting a third voltage indicating an amount of metal debris in oil. When the first voltage and the second voltage are approximately equal, the third voltage may be a first value equal to V_CC/2, as described in equation 1. When the first voltage and the second voltage are substantially different, the third voltage may be a second value. As further described inFIG.8, the first value may indicate an absence of metal debris in the oil and the second value may indicate a presence of metal debris in the oil.

A method800ofFIG.8may be implemented by a controller, such as the controller141ofFIG.1which includes a processor142and a memory144. The memory may hold instructions stored therein that, when executed by the processor, cause the controller to determine a presence and quantity of metal debris in oil using the oil sensor depicted inFIGS.4-6. As described in the method700ofFIG.7, the comparator of the oil sensor may compare voltages detected by the first inductor and the second inductor and output a value equal to the difference between the first voltage of the first inductor and the second voltage of the second inductor. The third voltage of the comparator may be output to the processor, which may perform the method800ofFIG.8to determine the presence and quantity of metal debris in the oil. The method800may further include alerting a user to the presence and quantity of metal debris.

The oil sensor may be in an ‘on’ state when the frequency generator is actuated to provide current to each of the first inductor and the second inductor to induce magnetic fields used to detect an amount of metal debris in the oil. At802, the method800includes actuating the frequency generator, as described in method700ofFIG.7. Actuating the frequency generator may include providing a voltage to the frequency generator, which may then generate a sinusoid or square wave. As described in the method700, the comparator outputs a voltage based on the difference between the first voltage and the second voltage of the first inductor and the second inductor, respectively.

At803, the method800includes estimating system operating conditions. When the oil sensor is implemented in a lubricating system of a vehicle, such as the vehicle100ofFIG.1, estimating operating conditions may include estimating oil temperature, whether the oil is circulating in the lubricating system or is stagnant, and so on.

At804, the method800includes determining if entry conditions have been met for metal debris sensing. For example, entry conditions may include operating conditions estimated/measured at803, such as the oil temperature being above a threshold temperature, where the threshold temperature may be 250° F. Entry conditions may further include that the oil is circulating through the lubrication system, a duration has elapsed since a last oil change, and so on. If entry conditions are not met, the method800proceeds to806, where the method800includes maintaining current vehicle operating parameter's. The oil sensor is thus not used to determine a presence of metal debris in the oil. The method800ends.

If at804, entry conditions have been met, the oil sensor is used to determine a presence of metal debris in the oil. At810, the method800includes analyzing the voltage from the comparator (e.g., the difference between the first voltage of the first inductor and the second voltage of the second inductor). The voltage is used to determine a presence and quantity of metal debris in the oil.

At812, the method800includes determining if metal debris is present. In one example, metal debris may be present in oil when the third voltage is above a positive, non-zero threshold value, such as VCC/2+2 mV. If the third voltage is below the threshold value, metal debris may not be detected by the oil sensor and therefore may not be present in the oil. If the third voltage is greater than or equal to the threshold value, metal debris may be detected by the oil sensor.

If metal debris is not present, the method800proceeds to814, where the method800includes outputting indication that no metal debris has been detected. For example, an indication may appear to a vehicle operator at a heads up display or other user interface that the oil is not degraded. In another example, the absence of a malfunction indicator light (MIL) may be interpreted by a user as a lack of oil degradation. When the oil sensor is implemented in a system other than a vehicle, the indication may be output to an external device. Whether or not a user is alerted to a lack of metal debris in the oil, the output indicating a status of oil degradation (or lack thereof) may be stored in the memory of the controller, along with a date and time at which the method was implemented.

Returning to812, if it is determined that metal debris is present in the oil, the method800proceeds to816. At816, the method800includes determining a quantity of metal debris present in the oil. In one example, the quantity may be determined based on the third voltage where a value of the third voltage may be mapped to a relative quantity of metal debris in the oil.

At818, the method800includes outputting an alert indicating the presence of metal debris. The alert may further include indication of the quantity of metal debris. A MIL may be illuminated, indicating degradation of oil. Further, a relative quantity of metal debris and/or an amount by which oil is degraded may be displayed to the user in a heads up display or other user interface. The alert may include indication that an oil replacement is desired to reduce further degradation of the oil and/or the vehicle system.

In this way, an oil sensor may be used to detect metal debris suspended in oil of a lubrication system based on inductance differences across two inductors of a circuit. Variations due to temperature variations may be reduced due to positioning of the two inductors in the oil sensor. The herein described oil sensor may have a reduced footprint and complexity compared to conventional oil sensors. As elements of the oil sensor are contained in housing, the oil sensor may be placed in a variety of environments, for example, in a channel of a lubrication system, in an oil reservoir, and so on. Mechanical deterioration may be reduced, as implementation of the herein described oil sensor may alert a user to a presence of metal debris in the oil and thus indicate a request for oil to be cleaned and/or replaced, which may remove the metal debris from the oil and reduce further degradation due to the cycling of metal debris through the lubrication system.

The disclosure also provides support for a system for metallic debris detection, comprising: a detection circuit including a first inductor and a second inductor, the second inductor shielded from an external environment, wherein the detection circuit generates an output based on a difference between a first voltage of the first inductor and a second voltage of the second inductor, where the difference indicates a presence of metallic debris within oil. In a first example of the system, the detection circuit comprises a first peak detector coupled to the first inductor, a second peak detector coupled to the second inductor, each of the first peak detector and the second peak detector coupled to a comparator, and each of the first inductor, the first peak detector, the second inductor, and the second peak detector are coupled to ground. In a second example of the system, optionally including the first example, the comparator compares voltages of the first inductor and the second inductor, as output by the first peak detector and the second peak detector respectively, to identify the difference between the first voltage and the second voltage. In a third example of the system, optionally including one or both of the first and second examples, the detection circuit is coupled to a control system which takes the difference between the first voltage and the second voltage as an input and uses the input to determine information about the presence and a quantity of metallic debris. In a fourth example of the system, optionally including one or more or each of the first through third examples, the first inductor is exposed to oil. In a fifth example of the system, optionally including one or more or each of the first through fourth examples, the second inductor is positioned behind the first inductor such that the second voltage of the second inductor is shielded from the external environment by the first inductor and an external case. In a sixth example of the system, optionally including one or more or each of the first through fifth examples, the system further comprises: a first spacer, a magnet, a second spacer, and a circuit board comprising the detection circuit, where the first spacer is between the first inductor and the magnet, and the second spacer is positioned between the magnet and the second inductor. In a seventh example of the system, optionally including one or more or each of the first through sixth examples, the first spacer, the magnet, the second spacer, the circuit board, the first inductor, and the second inductor are housed in an external case. In an eighth example of the system, optionally including one or more or each of the first through seventh examples, the external case formed of metal or non-magnetically inert material to shield the second inductor from the external environment. In a ninth example of the system, optionally including one or more or each of the first through eighth examples, the first inductor and the second inductor are each coupled to the circuit board via an electrical lead connection.

The disclosure also provides support for a method, comprising: pulling metal debris towards an external sensing element using a magnet, inducing a first magnetic field at the external sensing element and a second magnetic field at an internal comparison element, and comparing voltages of the external sensing element and the internal comparison element at a comparator to detect metal debris suspended in oil. In a first example of the method, metal debris in proximity to the external sensing element and subjected to the first magnetic field generate eddy currents opposing the first magnetic field. In a second example of the method, optionally including the first example, the eddy currents opposing the first magnetic field change a voltage of the external sensing element. In a third example of the method, optionally including one or both of the first and second examples, the second magnetic field is shielded by the external sensing element and a metallic case from eddy current effects. In a fourth example of the method, optionally including one or more or each of the first through third examples, the method further comprises: outputting an indication of a presence and a quantity of metal debris in oil to an external device when the voltages of the external sensing element and the internal comparison element are different. In a fifth example of the method, optionally including one or more or each of the first through fourth examples, the method further comprises: determining the presence and the quantity of metal debris in oil by comparing an output value with a lookup value table or threshold, and outputting the quantity at the external device. In a sixth example of the method, optionally including one or more or each of the first through fifth examples, the quantity of metal debris is a relative quantity. In a seventh example of the method, optionally including one or more or each of the first through sixth examples, outputting the quantity includes outputting a level of oil degradation. In an eighth example of the method, optionally including one or more or each of the first through seventh examples, the method further comprises: outputting an indication of an absence of metal debris in oil when the voltages of the external sensing element and the internal comparison element are equal.

The disclosure also provides support for a system, comprising: a lubricating system including an oil sensor, and a controller with instructions stored in non-transitory memory, that when executed, cause the controller to: induce a first magnetic field at an external sensing element and a second magnetic field at an internal comparison element, and detect a presence and a quantity of metal debris suspended in oil by comparing a first voltage of the external sensing element and a second voltage of the internal comparison element at a comparator.

FIGS.1-6show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. Moreover, unless explicitly stated to the contrary, the terms “first,” “second,” “third,” and the like are not intended to denote any order, position, quantity, or importance, but rather are used merely as labels to distinguish one element from another. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus or minus five percent of the range unless otherwise specified.

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