Patent Application
20230341043
This disclosure relates generally to cooling and lubricating electric vehicle drive systems. More specifically, this disclosure relates to improved cooling and lubrication of electric vehicle drive systems without requiring an electric fluid pump.
Recent advances in electric motor and battery technologies have made electric vehicles (EVs) practical to manufacture. Electric vehicles have a number of advantages over conventional internal combustion vehicles, including the dramatically reduced footprint of the engine and/or drive train components. Traction electric motors in EV applications require cooling to function properly throughout the drive cycle and torque spectrum. The current state of the art of the EV industry is to combine an electric motor and transmission to share the same housing and coolant/lubricant.
This disclosure relates to improved cooling and lubrication of electric vehicle drive systems without requiring an electric fluid pump. It should be noted that this disclosure is of an apparatus and method intended for use with traction or auxiliary drives, but may also be scaled for main power units.
In one embodiment, a drive unit lubrication and cooling system includes a lower sump disposed at a bottom of a housing for an electric motor/stator and drive train of an electric vehicle. The lower sump is configured to accumulate coolant/lubricant fluid that has passed through windings of the electric motor/stator. The lower sump includes a portion configured to receive part of one or more drive gears for the drive train. The drive unit lubrication and cooling system also includes an upper sump disposed above the electric motor/stator and drive train. The upper sump is configured to accumulate at least a portion of the coolant/lubricant fluid that has been moved by the one or more drive gears. The drive unit lubrication and cooling system further includes one or more electronically-controlled exit or entrance valves configured to be positioned between the upper sump and one or more spaces adjacent to the windings of the electric motor/stator. The one or more electronically-controlled exit or entrance valves are configured to release the coolant/lubricant fluid from the upper sump to flow by gravity through the one or more spaces adjacent to the windings of the electric motor/stator into the lower sump.
In another embodiment, a method of lubricating and cooling a drive unit includes accumulating, in a lower sump disposed at a bottom of a housing for an electric motor/stator and drive train of an electric vehicle, coolant/lubricant fluid that has passed through windings of the electric motor/stator. The lower sump includes a portion receiving part of one or more drive gears for the drive train. The method also includes accumulating, in an upper sump disposed above the electric motor/stator and drive train, at least a portion of the coolant/lubricant fluid that has been moved by the one or more drive gears. The method further includes electronically controlling one or more exit or entrance valves between the upper sump and one or more spaces adjacent to the windings of the electric motor/stator to release the coolant/lubricant fluid from the upper sump to flow by gravity through the one or more spaces adjacent to the windings of the electric motor/stator into the lower sump.
For either embodiment, the one or more drive gears may move some of the coolant/lubricant fluid through one or more spaces between the housing and the one or more drive gears.
For either embodiment, a one-way check valve may be interposed between (i) the upper sump and (ii) the one or more spaces between the housing and the one or more drive gears. The one-way check valve may be configured to admit the coolant/lubricant fluid from the one or more spaces between the housing and the one or more drive gears into the upper sump and to inhibit return of the coolant/lubricant fluid from the upper sump into the one or more spaces between the housing and the one or more drive gears.
For either embodiment, a drive controller may be configured to control the one or more exit or entrance valves to selectively release the coolant/lubricant fluid accumulated in the upper sump into the one or more spaces adjacent to the windings of the electric motor/stator.
For either embodiment, the drive controller may be configured to control the one or more exit or entrance valves based on heat generation by the windings of the electric motor/stator.
For either embodiment, the drive controller may be configured to use signals from one or more temperature sensors disposed proximate to the windings of the electric motor/stator to control the one or more exit or entrance valves.
For either embodiment, the one or more spaces between the housing and the one or more drive gears may form part of a baffling system for movement of the coolant/lubricant fluid from the lower sump towards the upper sump.
For either embodiment, a heat exchanger may be fitted to the upper sump and may be configured to disperse heat from the coolant/lubricant fluid accumulated in the upper sump.
For either embodiment, movement of the coolant/lubricant fluid through one or more spaces between the housing and the one or more drive gears may lubricate multiple drive gears of the drive train including the one or more drive gears.
For either embodiment, no electric fluid motor may be required to move the coolant/lubricant fluid from the lower sump to the upper sump.
Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
For a more complete understanding of this disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
In conventional combustion and electric vehicle designs, motors and reduction gear systems are typically installed in aluminum housings. Early drive unit designs used separate housing compartments with water cooling for a motor and gear oil to lubricate a transmission. Even with early EV designs, the electric motor was often cooled by a water jacket, which shares coolant with other vehicle components. This water jacket may wrap around the stator of an electric motor and cool the stator core by direct contact. One drawback to use of a water jacket is the increased packaging space and mass required to encompass the additional size of the water jacket around the electric motor.
In more recent EV designs, an electric motor is cooled using either a mechanical or electric pump to direct a combined coolant/lubricant fluid (such as automatic transmission fluid or “ATF”) over both the motor windings and the core of the stator for maximum heat rejection, while gears and bearings are lubricated by fluid splash. In some designs, the electric pump can be turned on/off to operate as a function of heat generation by the motor. That is, the electric pump operates when cooling is needed but turns off when no heat rejection required. This saves the power to operate the pump and leads to a more efficient system. Fluid splash lubrication of the gears and bearings continues during operation, regardless of whether the electric pump is on or off.
One approach to the drive units in such systems is to incorporate a “wet sump” design, where a volume of coolant/lubricant is located at a bottom of a drive unit and the electric pump draws fluid from this volume to cool the motor while the coolant/lubricant within the wet sump is agitated by rotating gears to splash fluid throughout the transmission. The efficiency of an integrated electric drive unit using a wet sump design is a function of the fluid fill level, instantaneous rotating component speed, and pump speed command.
The vehicle 100 of
Passengers may enter and exit the cabin 101 through at least one door 102 forming part of the cabin 101. A transparent windshield 103 and other transparent panels mounted within and forming part of the cabin 101 allow at least one passenger (referred to as the “operator,” even when the vehicle 100 is operating in an advanced driving or “AD” mode) to see outside the cabin 101. Rear-view mirrors 104 mounted to sides of the cabin 101 enable the operator to see objects to the sides and rear of the cabin 101 and may include warning indicators (such as selectively illuminated warning lights) for features such as blind spot warning (indicating that another vehicle is in the operator's blind spot) and/or lane departure warning.
Wheels 105 mounted on axles that are supported by the chassis and driven by the motor(s) via drive gears (all not visible in
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By way of example, power doors on a vehicle may be operated by an ECU called the body control module (not shown in
Notably, vehicle control systems are migrating to higher-speed networks with an Ethernet-like bus for which each ECU is assigned an Internet protocol (IP) address. Among other things, this may allow both centralized vehicle ECUs and remote computers to pass around huge amounts of information and participate in the Internet of Things (IoT).
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In the design illustrated in
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One or more drive gears 501 are closely encased by a housing 502, where coolant/lubricant fluid between the drive gear(s) 501 and the housing 502 is agitated by rotation of the drive gear(s) 501. The rotation and agitation result in splash lubrication of the drive gear(s) 501 and also coolant/lubricant fluid flowing into a baffling system 503. The baffling system 503 conducts the coolant/lubricant fluid toward the upper sump 304, where the one-way check valve 303 admits the coolant/lubricant fluid from the baffling system 503 into the upper sump 304 while preventing return flow from the upper sump 304 into the baffling system 503. The agitation and baffling system thus replaces an electric fluid pump in moving coolant/lubricant fluid from the lower sump 301 into the upper sump 304.
Pressurized cooling using an electric fluid pump has the capacity to adjust flow rate by altering pump speed/pressure, thus correlating coolant/lubricant fluid flow with the motor heat generation. The power output of an electric machine is dependent on the ability to remove heat from the motor, so more effective heat removal results in higher continuous motor output power. Typically, pressurized oil cooling results in good heat removal. However, pressurized cooling requires additional components to pressurize and pump the fluid throughout the motor, such as through the use of a heat exchanger, oil filter and an electric fluid pump, which adds to weight and production cost. By contrast, systems that feed coolant/lubricant by gravity over electric motors, as described for the present disclosure, have the potential for somewhat limited functionality from a cooling standpoint, being constrained to feeding non-pressurized coolant/lubricant fluid at flow rates defined by the orifice passageway sizes and (in previous designs) having no correlation over real-time motor actual heat generation/removal requirement. Thus, prior designs for gravity fed cooling are considered slightly less effective than pressurized cooling. The following describes how the drive unit lubrication and cooling system 300 may be designed to overcome these types of issues.
In the drive unit lubrication and cooling system 300, the upper sump 304 accumulates coolant/lubricant fluid. Rotation 601 of one or more drive gears shown in
Under control of the drive unit controller for the drive unit lubrication and cooling system 300, as needed for cooling, the coolant/lubricant fluid accumulated in the upper sump 304 is released by electronically controlling the one or more exit or entrance valves 305 to flow by gravity down through the electric motor/stator windings 306. This is shown as one or more paths 603 in
With the approach of the present disclosure, the electric drive unit uses the combination of splash lubrication and the upper sump 304 to cool a motor and gearbox, removing the need for an electric fluid pump. This approach can improve overall drive unit efficiency, as there is no power draw for an electric or mechanical fluid pump, and reduce the cost of implementation by eliminating the electric fluid pump. The drive unit controller in the powertrain CAN 203 can determine when to provide cooling to motor end windings based on heat generation and, by controlling the electronically-controlled exit or entrance valve(s) 305, allow correlation of coolant/lubricant fluid flow with the motor heat generation.
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It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.
The description in the present disclosure should not be read as implying that any particular element, step, or function is an essential or critical element that must be included in the claim scope. The scope of patented subject matter is defined only by the allowed claims. Moreover, none of the claims invokes 35 U.S.C. § 112(f) with respect to any of the appended claims or claim elements unless the exact words “means for” or “step for” are explicitly used in the particular claim, followed by a participle phrase identifying a function. Use of terms such as (but not limited to) “mechanism,” “module,” “device,” “unit,” “component,” “element,” “member,” “apparatus,” “machine,” “system,” “processor,” or “controller” within a claim is understood and intended to refer to structures known to those skilled in the relevant art, as further modified or enhanced by the features of the claims themselves, and is not intended to invoke 35 U.S.C. § 112(f).
While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.
