Patent Application
20210010766
The present invention relates generally to the electric drive train of an electric vehicle and, more particularly, to a thermal management system that can be used to manage the cooling and lubrication system associated with an electric vehicle's drive train, thereby reducing energy consumption.
In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drive trains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drive train, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost.
The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drive train in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at a reduced level compared to a conventional vehicle. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drive train of a hybrid vehicle is typically much more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, or multiple electric motors, thereby eliminating one source of pollution while significantly reducing drive train complexity.
In order to achieve the desired levels of performance and reliability in an electric vehicle the drive train assembly must be lubricated and cooled, with the temperature of the traction motor remaining within its specified operating range regardless of ambient conditions or how hard the vehicle is being driven. A variety of approaches have been used to try and meet these goals. For example, U.S. Pat. No. 7,156,195 discloses a cooling system for use with the electric motor of a vehicle. The refrigerant used in the cooling system passes through an in-shaft passage provided in the output shaft of the motor as well as the reduction gear shaft. A refrigerant reservoir is formed in the lower portion of the gear case while an externally mounted cooler is used to cool the refrigerant down to the desired temperature.
U.S. Pat. No. 7,489,057 discloses a rotor assembly cooling system utilizing a hollow rotor shaft. The coolant feed tube that injects the coolant into the rotor shaft is rigidly coupled to the rotor shaft using one or more support members. The coolant that is pumped through the injection tube flows against the inside surface of the rotor shaft, thereby extracting heat from the assembly. The coolant circuit includes a coolant reservoir. The coolant used to extract heat from the motor is also used to cool and lubricate the transmission in at least one disclosed embodiment.
Although the prior art discloses numerous techniques for maintaining the temperature of the drive train assembly, an improved thermal management system is needed that efficiently controls drive train assembly temperature. The present invention provides such a thermal management system.
The present invention provides a multi-mode thermal management system that includes (i) a drive train thermal control loop, (ii) a second thermal control loop, (iii) a heat exchanger thermally coupled to both the drive train thermal control loop and to the second thermal control loop, and (iv) a bypass valve, where the bypass valve in a first operational mode thermally decouples the drive train thermal control loop from the second thermal control loop, and where the bypass valve in a second operational mode thermally couples the drive train thermal control loop to the second thermal control loop via the heat exchanger. The drive train thermal control loop includes a first circulation pump which circulates a first heat transfer fluid within the drive train thermal control loop, where the drive train thermal control loop is thermally coupled to a drive train assembly (e.g., vehicle propulsion motor(s), gear assembly, etc.). The second thermal control loop includes a second circulation pump which circulates a second heat transfer fluid, different from the first heat transfer fluid, within the second thermal control loop. The second thermal control loop is preferably thermally coupled to a power inverter. The bypass valve is configured to operate in the first operational mode when a temperature corresponding to the first heat transfer fluid is less than a preset temperature, and configured to operate in the second operational mode when the temperature corresponding to the first heat transfer fluid is greater than the preset temperature. The second thermal control loop may include a radiator and a fan configured to force air through the radiator. The first heat transfer fluid may consist of oil and the second heat transfer fluid may consist of water or water containing an additive (e.g., ethylene glycol, propylene glycol, etc.). The bypass valve may consist of a thermostatic valve or it may be controlled by a control system that monitors the temperature of the first heat transfer fluid.
In one aspect, the bypass valve may be coupled to the drive train thermal control loop, where the bypass valve in the first operational mode thermally decouples the drive train thermal control loop from the heat exchanger and allows the first heat transfer fluid within the drive train thermal control loop to bypass the heat exchanger, and where the bypass valve in the second operational mode thermally couples the drive train thermal control loop to the heat exchanger.
In another aspect, the bypass valve may be coupled to the second thermal control loop, where the bypass valve in the first operational mode thermally decouples the second thermal control loop from the heat exchanger and allows the second heat transfer fluid within the second thermal control loop to bypass the heat exchanger, and where the bypass valve in the second operational mode thermally couples the second thermal control loop to the heat exchanger.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
It should be understood that the accompanying figures are only meant to illustrate, not limit, the scope of the invention and should not be considered to be to scale. Additionally, the same reference label on different figures should be understood to refer to the same component or a component of similar functionality.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “includes”, and/or “including”, as used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” and the symbol “/” are meant to include any and all combinations of one or more of the associated listed items. Additionally, while the terms first, second, etc. may be used herein to describe various steps, calculations or components, these steps, calculations or components should not be limited by these terms, rather these terms are only used to distinguish one step, calculation or component from another. For example, a first calculation could be termed a second calculation, similarly, a first step could be termed a second step, similarly, a first component could be termed a second component, all without departing from the scope of this disclosure.
The cooling systems described and illustrated herein are generally designed for use in a vehicle using an electric motor, e.g., an electric vehicle. In the following text, the terms “electric vehicle” and “EV” may be used interchangeably and may refer to an all-electric vehicle, a plug-in hybrid vehicle, also referred to as a PHEV, or a hybrid vehicle, also referred to as a HEV, where a hybrid vehicle utilizes multiple sources of propulsion including an electric drive system. The term “battery pack” as used herein refers to an assembly of one or more batteries electrically interconnected to achieve the desired voltage and capacity, where the battery assembly is typically contained within an enclosure.
In an EV, typically the battery pack as well as several other components are coupled to an active thermal management system. The thermal management system may consist of a single coolant loop or of several coolant loops. When the thermal management system includes multiple coolant loops, the loops may operate independently or be interconnected, for example utilizing heat exchangers. Depending upon the coolant loop configuration and the components to be cooled, the coolant may consist of a traditional coolant (e.g., water with an additive such as ethylene glycol or propylene glycol), a refrigerant, or a coolant that is designed to provide lubrication as well as extract heat (e.g., oil). Typically a refrigerant is used with the passenger cabin's heating, ventilation and air conditioning (HVAC) system, a more traditional coolant is used for the battery pack and power inverter, and a lubricating coolant is used for the drive train assembly (e.g., motor and gear assembly).
Within coolant loop 101 the heat transfer fluid is circulated using coolant pump 109. Preferably the heat transfer fluid is water-based, e.g., pure water or water that includes an additive such as ethylene glycol or propylene glycol, although a non-water-based heat transfer fluid may also be used in coolant loop 101. Coolant loop 101 is thermally coupled to power inverter 103. In order to passively cool power inverter 103 as well as any other components directly coupled to coolant loop 101, the coolant is circulated through radiator 111. If there is insufficient air flow through radiator 111 to provide the desired level of passive cooling, for example when the vehicle is stopped or driving at low speeds, a fan 113 may be used to force air through the radiator.
Coolant loop 105, which is coupled to drive train assembly 107 as previously noted, uses a coolant pump 115 to circulate a coolant through drive train assembly 106, the coolant being capable of both extracting heat and lubricating the drive train as it circulates. The coolant used in loop 105 is non-gaseous and has the thermal and mechanical properties suitable for a motor coolant and lubricant, e.g., high heat capacity, high break-down temperature, relatively low viscosity, and a good lubricant in order to protect against drive train assembly wear and corrosion. For most motor designs it is also necessary that the coolant be electrically non-conductive. In the preferred embodiment oil is used as the coolant within loop 105.
In
It will be appreciated that the exemplary thermal management system shown in
The purpose of the thermal management system, regardless of its specific configuration, is to efficiently regulate the temperature of the various subsystems and components thermally coupled to the system, thereby optimizing performance of each. Thus, for example, a typical EV thermal management system must regulate the temperature within the passenger cabin, the battery pack, the drive train, and the power inverter in order to ensure that the passengers within the passenger cabin are comfortable and that the various EV subsystems (e.g., battery pack, drive train and power inverter) are operating at peak efficiency. In order to accomplish this goal, heat generated within one system is used to heat other systems while excess heat is rejected using active refrigeration systems as well as radiators and blower fans.
A common practice in an EV thermal management system, regardless of its exact configuration, is to thermally couple the power inverter coolant loop and the drive train assembly coolant loop via a heat exchanger as illustrated in
In an electric motor, energy consumption varies based on the temperature of the coolant/lubricant, i.e., the coolant within coolant loop 105. The temperature dependence is due to (i) viscous drag (i.e., fluid resistance) and (ii) preload force (i.e., drag) on the drive train assembly's bearings and seals. Viscous drag, which affects both rotor rotation within the motor and rotation of the gears within the drive train's transmission, is dependent upon the viscosity of the oil, e.g., coolant, used to cool and lubricate the drive train. Low temperature also increases the preload force applied to the bearings and seals within the drive train, which results in lowering the efficiency. Additionally, it will be appreciated that viscous drag and bearing/seal preload force is also applicable to operation of the coolant pump used within the drive train assembly coolant loop, e.g., pump 115 in coolant loop 105.
In order to achieve the desired increase in drive train efficiency, and in accordance with the invention, a bypass valve is introduced into the thermal management system that effectively thermally decouples the drive train assembly coolant loop 105 from other coolant loops within the thermal management system. Introduction of the bypass valve allows the coolant within loop 105 to heat-up more rapidly. Accelerating the heat-up cycle of the coolant within loop 105 lowers drive train energy consumption which, in turn, leads to improved driving range.
Once the coolant within the drive train assembly coolant loop has reached the desired operating temperature, the bypass valve (e.g., valve 401, 501, 601, 701) is opened, thereby thermally coupling the coolant loop to the power inverter coolant loop via the heat exchanger (e.g., heat exchanger 117). Preferably the desired operating temperature is either set to the optimal operating temperature of the drive train assembly or set to a temperature that is sufficiently high to minimize the effects of coolant viscosity and density on the operating efficiency of the drive train assembly and coolant pump 115. In at least one embodiment the bypass valve is a thermostatic valve configured to open when the desired coolant temperature has been reached. Alternately the bypass valve may be controlled by a control system that monitors coolant temperature within coolant loop 105 and opens the bypass valve when the desired operating temperature has been reached.
Systems and methods have been described in general terms as an aid to understanding details of the invention. In some instances, well-known structures, materials, and/or operations have not been specifically shown or described in detail to avoid obscuring aspects of the invention. In other instances, specific details have been given in order to provide a thorough understanding of the invention. One skilled in the relevant art will recognize that the invention may be embodied in other specific forms, for example to adapt to a particular system or apparatus or situation or material or component, without departing from the spirit or essential characteristics thereof. Therefore the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention.
