Patent Publication Number: US-2004045749-A1

Title: Cooling system and method for a hybrid electric vehicle

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to a hybrid electric vehicle, and specifically to a system and method to meet the cooling needs of a hybrid electric vehicle&#39;s motor, such as an integrated-starter-generator, using a transmission cooling loop that flows through a specialized stator housing of the motor.  
       BACKGROUND OF INVENTION  
       [0002] The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.  
       [0003] The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.  
       [0004] Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.  
       [0005] A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a “split” parallel/series configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier gear. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.  
       [0006] The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize the HEV&#39;s potential benefits.  
       [0007] One such area of HEV development is addressing the cooling needs of several new components to the HEV. For example, to achieve better fuel economy, an HEV can use an integrated-starter-generator (ISG) for starting and stopping the engine, providing boost to the powertrain, generating electrical charge, and regenerative braking. In some HEV configurations, the ISG can be located between the engine and the transmission. The engine, ISG, and transmission all operate at high temperatures and need to be carefully cooled to maintain reliable and efficient operation. In a typical vehicle environment the powertrain is enclosed and lacks sufficient air-flow to provide adequate cooling needs. Therefore, active coolant management is needed.  
       [0008] Vehicle coolant management is certainly known in the art, and in fact coolant management within an HEV is known. See generally, U.S. Pat. No. 6,213,233 to Sonntag et al. Some patents also address cooling needs for prior art generators. See generally, U.S. Pat. No. 6,046,520 and U.S. Pat. No. 6,326,709 to Adelmann et al. Known prior art ISG cooling uses either airflow cooling or a separate active cooling system including a separate electric pump, cooling line, and heat exchanger. The air cooling method is not sufficient for most rear wheel drive configurations, or any configuration with poor airflow around the powertrain. Unfortunately, there is no known prior art for cost effective and efficient cooling of an ISG in an HEV.  
       SUMMARY OF INVENTION  
       [0009] Accordingly, the present invention relates generally to a hybrid electric vehicle (HEV), and specifically to a system and method to meet the cooling needs of a HEV&#39;s motor, such as an integrated-starter-generator (ISG), using a transmission cooling loop that flows through a specialized stator housing of the motor.  
       [0010] Specifically, the invention provides a cooling system having a cooling loop with a heat exchanger and conduits in heat conductive contact with the stator housing of the motor, transmission, and heat exchanger. Coolant flows through the cooling loop through the action of either a mechanical transmission pump or an auxiliary pump or both. The auxiliary pump is needed specifically when the engine is in idle or is not operating. In one embodiment of the present invention, a controller receives and processes input from at least one vehicle sensor, and commands the auxiliary pump to operate when the processed input of at least one vehicle sensor exceeds a pre-selected threshold.  
       [0011] In an alternate embodiment of the present invention, the cooling loop also has bypass conduits and bypass valves having actuators independently controllable by the controller to operate when the processed input from at least one vehicle sensor exceeds a pre-selected threshold and the auxiliary pump is reversible. The auxiliary pump can be electric and either internal or external to the vehicle transmission.  
       [0012] The system can be configured to maintain a transmission temperature at no greater than 250 degrees Fahrenheit and a temperature for the motor at no greater than 350 degrees Fahrenheit.  
       [0013] The stator housing can be configured to be overlapped by a transmission housing or adjacent to a transmission housing.  
       [0014] Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0015] The foregoing objects, advantages, and features, as well as other objects and advantages, will become apparent with reference to the description and figures below, in which like numerals represent like elements and in which:  
     [0016]FIG. 1 illustrates a prior art vehicle cooling system;  
     [0017]FIG. 2 illustrates an ISG vehicle cooling system of the present invention;  
     [0018]FIG. 3 illustrates an alternate embodiment ISG vehicle cooling system of the present invention;  
     [0019]FIG. 4 illustrates one embodiment of an ISG stator housing of the present invention; and  
     [0020]FIG. 5 illustrates an alternate embodiment of an ISG stator housing of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0021] The present invention relates to electric vehicles and, more particularly, hybrid electric vehicles (HEVs). The present invention provides a cooling system for an electric vehicle&#39;s motor. The illustrated embodiment describes the electric motor as an integrated-starter-generator (ISG), though the invention can apply to any electric motor.  
     [0022] To assist in understanding the present invention, FIG. 1 illustrates a simplified conventional prior art vehicle cooling system for a vehicle generally described at  20  having an internal combustion engine (engine)  22  and an automatic transmission (transmission)  24 . This conventional cooling system  20  has an engine cooling loop  26  and an independent transmission cooling loop  28 .  
     [0023] In the engine cooling loop  26 , coolant (not shown) is fed from the engine  22  to an inlet of a heat exchanger, such as a radiator  30 , via a first conduit  32 , such as hoses, piping, and other means known in the art. Coolant exits the radiator  30  and returns to the engine  22  via a second conduit  34 . Waste heat is removed from the engine  22  by the coolant and transported through the engine cooling loop  26  via the conduits  32  and  34  through the action of a first pump  36  driven by the engine  22 .  
     [0024] In the transmission cooling loop  28 , transmission oil (not shown) is fed from the transmission  24  to an inlet of a separate heat exchanger, such as a transmission oil cooler  44 , via a third conduit  42 , such as hoses, piping, and other means known in the art. The transmission oil exits the oil cooler  44  and returns to the transmission  24  via a fourth conduit  46 . Waste heat is removed from the transmission  24  by the transmission oil and transported through the transmission cooling loop  28  via the conduits  42  and  46  through the action of a second pump  48  driven by, for example, the transmission  24 .  
     [0025] Another separate heat exchanger, an air conditioner (A/C) condenser  50 , is also illustrated in FIG. 1. Many other possible packaging orders of these heat exchangers within the airflow are possible using the present invention. For example, the transmission air cooler  44  could be located in front of a cooling airflow  38  to the A/C condenser  50 .  
     [0026] All waste heat traveling through cooling loops  26  and  28  is removed/vented from the vehicle by the cooling airflow  38  as it passes through the various illustrated heat exchangers, i.e., the radiator  30 , transmission oil cooler  44 , and A/C condenser  50 . The cooling airflow  38  can vary based on vehicle speed and ambient air temperature, and can be increased by the action of a fan  40 . The fan  40  can be driven, for example, by the engine  22  or as illustrated in FIG. 1, by a separate electric motor  52 .  
     [0027] An auxiliary pump, such as an auxiliary electric oil pump (auxiliary pump)  49  known in the art, can also be added to the transmission cooling loop  28  to pressurize some of the transmission oil systems when the vehicle is stopped or the engine is off, i.e., the mechanical transmission pump, the second pump  48 , is not operating. When the engine  22  is in operation, the second pump  48  can supply the transmission systems with oil alone or in combination with the auxiliary pump  49 . In one embodiment, the mechanical transmission pump can deactivate the auxiliary pump  49 . The auxiliary pump  49  can be located at various places within the transmission cooling loop  28  including inside a transmission oil pan  23 .  
     [0028] The present invention provides a thermal management strategy for an HEV having an electric motor such as an ISG. An ISG generates significant additional waste heat to the vehicle powertrain and should have active cooling. An independent ISG cooling system would negatively impact fuel economy and add additional hardware, components, maintenance, cost, and weight to a vehicle. The present invention solves these shortcomings with minimal vehicle modifications by using the existing transmission cooling system loop. This includes using an auxiliary pump, such as described above, to transport transmission oil through a transmission-cooling loop further routed through an ISG cooling jacket, even when the engine and transmission are not running. Use of the transmission cooling circuit to cool both an ISG and transmission is possible since the preferred ISG and transmission operating temperatures are similar. The increased cooling demand of the combined ISG and transmission cooling loop can easily be accommodated using a larger transmission oil cooler and properly sized auxiliary pump for the transmission oil.  
     [0029] Using the present invention, an auxiliary electric oil pump within the transmission cooling loop could also be switchable, through a valve in a hydraulic valve body of the transmission for example, to bypass fluid around an ISG stator housing or jacket (i.e., the non-moving portion of the ISG) when the ISG cooling needs are minimal and through the rest of the transmission cooling loop when the engine is running. The auxiliary electric oil pump can be switched back to cooling the ISG stator jacket when the engine is off or ISG cooling needs are high. A larger volume oil pan may be necessary to accommodate the additional fluid volume of this modified transmission cooling loop. The auxiliary pump currently used in prior art transmission applications may need to be enlarged to accommodate the added cooling flow requirements. Although the auxiliary pump in the prior art is located inside the transmission oil pan, it could be externally mounted to package a larger motor needed to drive the pump. The transmission oil cooler would similarly need to increase in size, but because of its relatively small size in the art, there should be adequate package space available within a vehicle.  
     [0030]FIG. 2 illustrates a vehicle cooling system for an HEV having an ISG using an embodiment of the present invention and is generally indicated at  60 . The illustrated HEV powertrain configuration has an internal combustion engine (engine)  62  (in one embodiment, the engine  62  can be a  3 . 5 -liter engine known in the art), an integrated starter generator (ISG)  63 , and an HEV transmission  64  in a series arrangement. The HEV cooling system  60  has an HEV engine cooling loop  66 , a combined ISG/transmission cooling loop  68 , an A/C condenser cooling loop  88  and an independent inverter/converter cooling loop  69 .  
     [0031] In the HEV engine cooling loop  66 , coolant (not shown) is fed from the HEV engine  62  to an inlet of a heat exchanger, such as an HEV radiator  70 , via a fifth conduit  72 , such as hoses, piping, etc. Coolant exits the HEV radiator  70  and returns to the engine  62  via a sixth conduit  74 . Waste heat is removed from the HEV engine  62  by the coolant and transported through the HEV engine cooling loop  66  via the conduits  72  and  74  through the action of a third pump  76  that can be driven by the engine  62 . The ISG/transmission cooling loop  68  is in a heat conductive contact with the ISG  63  and HEV transmission  64 .  
     [0032] In the enclosed ISG/transmission cooling loop  68 , transmission oil (not shown) is fed from the ISG  63  to an inlet of a heat exchanger, such as an ISG/transmission oil cooler  78 , via a seventh conduit  80 , such as hoses, piping, etc. The transmission oil exits the ISG/transmission oil cooler  78  and returns to the HEV transmission  64  via an eighth conduit  82 . The transmission oil can carry waste heat out of the ISG  63  by flowing through an ISG stator housing described below. From the HEV transmission  64 , the transmission oil can flow back to the ISG  63  via a ninth conduit  84 . Waste heat is removed from the ISG  63  and transmission  64  by the transmission oil and transported through the ISG/transmission cooling loop  68  via the conduits  80 ,  82 , and  84  through the action of either an auxiliary pump such as an ISG/transmission pump  86  or an HEV mechanical transmission pump  87  or both. The ISG/transmission pump  86  can be electrical or external or internal to the transmission as described above.  
     [0033] A controller such as a vehicle control system (VCS)  91 , through a communication network, such as a controller area network (CAN)  95 , can control the ISG/transmission pump  86  and even an HEV fan  106  speed using vehicle inputs  93 . Vehicle inputs  93  can include vehicle speed, ambient temperature, coolant temperature sensors within the ISG  63  and the HEV transmission  64 . The VSC  91  can control the speed of the ISG/transmission pump  86  and HEV fan  106  based on predetermined values to maintain optimal operating temperatures for both the HEV transmission  64  and the ISG  63 . The VSC  91  and the CAN  54  can include one or more microprocessors, computers, or central processing units operatively connected and in communication with one or more computer readable devices; one or more memory management units; and input/output interfaces for communicating with various sensors, actuators and control circuits known in the art. A program of control logic can be embodied within the controller to interpret sensor signals (output) and to issue a command signal based on said interpretation to control the ISG/transmission cooling loop  68  when the processed input of at least one vehicle sensor exceeds a pre-selected threshold. For example, the controller can receive and process input from at least one vehicle sensor and command the auxiliary pump to operate when the processed input of at least one vehicle sensor exceeds a pre-selected threshold.  
     [0034] Also included in this HEV cooling system  60  schematic are the HEV A/C condenser  88  and the inverter/converter cooling loop  69 . The inverter/converter cooling loop  69 , is similar to the other cooling loops having coolant carrying waste heat flowing through an inverter  90  and DC/DC converter  92  to an electronic module cooler  94  through the action of an inverter/converter coolant pump  96  driven by an electric motor via additional conduits  98 ,  100 , and  102   
     [0035] Generally, all waste heat traveling through cooling loops  66 ,  68  and  69  is removed/vented from the vehicle by a cooling airflow  104  as it passes through the various heat exchangers, i.e., the HEV radiator  70 , ISG/transmission oil cooler  78 , HEV A/C condenser  88 , and electronic module cooler  94 . The cooling airflow  104  varies based on vehicle speed and ambient air temperature, and can be increased by the action of the HEV fan  106 . In one embodiment, the fan  106  can be driven by a 42-volt electric fan  107  known in the art. Again, many possible packaging orders of the various heat exchangers within the airflow is possible.  
     [0036] An alternate embodiment using the present invention could also place a coolant bypass system around the HEV transmission  64  or the ISG  63 . The bypass could be controlled to limit transmission oil flow into the HEV transmission  64  and the ISG  63  until each component reaches its optimal operating temperature at start-up.  
     [0037] Appropriate valves and controllers would need to be added as well (see FIG. 3, discussed below). For example, a transmission&#39;s optimal operating temperature can be 180 degrees Fahrenheit with a 250 degrees Fahrenheit peak. The ISG  63  optimal operating temperature can be hotter at 350 degrees Fahrenheit with a 350 degrees Fahrenheit peak. Therefore, the system could be configured to keep the ISG transmission cooler  78  or at least size the HEV fan  106  and ISG/transmission cooler  78  to never allow a temperature for the transmission oil to exceed 250 degrees Fahrenheit and to never allow a temperature for the oil in the ISG  63  greater than 350 degrees Fahrenheit. The ISG transmission pump  86  could be a reversible pump to add flexibility to the overall ISG/transmission cooling loop  68 . For example, the ISG/transmission cooling loop  68  can reverse flow at an ISG  63  startup to bring waste heat from the ISG  63  back to the HEV transmission  64  until an optimal operating temperature for the HEV transmission  64  is reached. Thus, this added flexibility could improve vehicle performance and efficiency.  
     [0038]FIG. 3 illustrates an example of an alternate embodiment of the present invention. FIG. 3 adds additional valves having actuators controllable by the VSC  91  known in the art, the ISG transmission pump  86  is reversible, and some additional transmission oil fluid paths (bypass conduits). Specifically, this alternate embodiment adds independently controllable valves  81 ,  83 , and  85 . The VSC  91  can control the valves when the processed input from at least one vehicle sensor exceeds a pre-selected threshold to divert transmission oil to the HEV transmission  64  or the ISG  63  or to bypass conduits  99  and  89 .  
     [0039]FIGS. 4 and 5 illustrate alternate embodiments of an ISG  63  stator housing using the present invention. In FIG. 4, the ISG  63  has an integral stator housing  108  in which to pass transmission oil and is partially covered by a transmission housing  110 .  
     [0040] In FIG. 5, the alternate embodiment ISG  63  has an integral stator housing  112  in which to pass transmission oil and is adjacent to a transmission housing  114 . The housing illustrated in FIG. 4 is preferred from the perspective of size since this configuration allows more floor pan clearance.  
     [0041] The above-described embodiments of the invention are provided purely for purposes of example. Many other variations, modifications, and applications of the invention may be made.