Abstract:
Temperature of an electric drive is regulated to prevent undesirable thermal effects. Temperature conditions of the electric drive system are monitored and torque of the electric drive system is limited based on the temperature conditions.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is related to thermal management in powertrains having an electric drive system. 
       BACKGROUND 
       [0002]    It is known to utilize electric drive systems in vehicle powertrains to drive or boost power at an output shaft. In addition, it is desirable to recover kinetic energy of the vehicle and store such recovered energy in energy storage device. Electric motors of electric drive systems have provided one convenient method for this bi-directional flow of energy to and from an output shaft. One aspect of utilizing such an electric drive system is managing the buildup of heat within system components. Electrical components are frequently sensitive to over temperature conditions, and it is beneficial to operate these components at temperatures that promote efficient operation and avoid undesirable thermal effects. 
       SUMMARY 
       [0003]    A method for regulating the temperature of an electric drive includes monitoring temperature conditions at predetermined locations in the electric drive system and attenuating maximum allowable torque of the electric drive system based on the monitored temperature conditions. Preferably, the predetermined locations include a power inverter module and an electric motor assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0005]      FIG. 1  is a block diagram of an exemplary electric drive system and control in accordance with the present disclosure; 
           [0006]      FIG. 2  is a block diagram of an alternate exemplary electric drive system and control in accordance with the present disclosure; 
           [0007]      FIG. 3  illustrates a three-phase power inverter module in accordance with the present disclosure; 
           [0008]      FIG. 4  is an exemplary plot of maximum torque allowed versus temperature conditions of the electric drive system in accordance with the present disclosure; 
           [0009]      FIG. 5  is an alternate exemplary plot of maximum torque allowed versus temperature conditions of the electric drive system in accordance with the present disclosure; and 
           [0010]      FIG. 6  is an exemplary plot of maximum torque allowed versus angular velocity of the electric motor assembly related to an exemplary sensor diagnostic and control in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIG. 1  illustrates a hybrid drive system  10  which has been constructed in accordance with the present disclosure. The hybrid drive system  10  illustrates a usage of an electric drive system  40 , an internal combustion engine  30 , and a transmission assembly  20 . The transmission assembly  20  provides output power to a driveline via an output shaft (not separately illustrated). The electric drive system  40  includes an energy storage device  50 , a power inverter module  60 , an electric motor assembly  70 , and a control module  80 . Energy storage device  50  can be a battery or bank of batteries, but it may be any electrical or electrochemical storage device and is not intended to be limited thereto. Power inverter module  60  switches AC electrical power to DC and DC electrical power to AC. Power inverters are well known in the art and will not be described in detail herein. Electric motor assembly  70  utilizes an electric motor in a motoring mode to convert AC electrical power into rotational power in the form of a spinning shaft. The same electric motor assembly may operate the electric motor in a generating mode, accepting rotational power through the spinning shaft and generating AC electrical power. This ability of an electric motor to operate in motoring or generating modes is well known in the art and will not be described in detail herein. The torque output of electric motor assembly  70  is defined as either the torque applied by the motor to the output shaft or the torque accepted by the electric motor from the output shaft. The ability of the electric motor assembly  70  to operate as a motor or generator enables the electric drive system  40  to operate in two manners: first, the system may provide power to a driveline from stored energy; second, the system may convert power from a driveline to stored energy. In order to provide power to the driveline, energy storage device  50  supplies DC electric power to power inverter module  60 . Power inverter module  60  converts the DC electric power to AC electric power. This AC power is used to drive electric motor assembly  70  and, subsequently, transmission assembly  20 . In order to convert rotational kinetic energy from the driveline to stored energy, the electric motor assembly  70  receives rotational energy from transmission assembly  20  and converts the energy to AC electrical power. This AC electrical power is transferred from electric motor assembly  70  to power inverter module  60  and is, thereby, converted to DC electrical power. This DC electrical power is used to charge the energy storage device  50 . 
         [0012]    As with any electrical process, some of the electrical power is converted in the electric drive system  40  to heat. Primary sources of electrically generated heat comes from, for example, switching losses in the inverter electronics, simple ohmic (I 2 R) losses and motor losses predominantly in motor windings. In addition, frictional forces in the electric motor assembly  70  also create heat in the electric drive system  40 . Heat generated in or transferred to electric drive system  40  may raise the temperature of all of the components in the system, and elevated temperatures pose a risk of thermal damage. Thermal damage occurs at a particular point in a component when the temperature at that point exceeds the thermal limit of a particular material or structure. Different operating conditions of the overall application in which electric drive system  40  is used may create various different localized higher temperatures in particular components. Whether electric drive system  40  is in an over temperature condition such that components are at thermal risk from localized higher temperatures can be difficult to monitor without a multitude of distributed sensors in the system. Control module  80  instead samples temperature data from predetermined indicative components, preferably power inverter module  60  and electric motor assembly  70 , processes this temperature data, and models the overall temperature condition of the system. Temperature sensors  65  and  75  are located on the power inverter module  60  and electric motor assembly  70 , respectively, to gather temperature data for use by control module  80 . The temperature condition developed from the sensor data is then utilized by programmed algorithms within control module  80 . These algorithms are programmed with threshold temperature condition set points, which, when exceeded, cause control module  80  to begin modulation of the electric motor assembly  70  by imposing certain torque control of the motor of the electric motor assembly  70 . Under acceptable thermal operating conditions, a maximum continuous torque function is applied to the electric motor assembly  70  as a function of temperature condition of the electric drive system  40  which effectively makes available torque up to the torque capability of the electric motor. Under unacceptable thermal operating conditions, the maximum continuous torque function is attenuated as described further herein below. Under unacceptable thermal operating conditions, or over temperature conditions, the maximum continuous torque function introduces an increasingly restrictive torque reduction factor into the controlling logic of the electric motor assembly  70 , thereby reducing the motor power throughput. As the temperature reaches the threshold temperature condition set point, a relatively minor reduction factor is introduced to the control logic whereby the maximum torque allowable motor torque is reduced relative to the motor torque capability. As the temperature continues to increase past the threshold temperature condition set point, the attenuation of motor torque becomes more aggressive and hence the reduction factor becomes more significant. In some embodiments, an indicator light or driver warning system is utilized to provide information to the driver in the event that one of the set points is reached. And, additional set points may correspond to even higher temperature conditions. In the event that the temperature condition exceeds a critical temperature condition set point, control module  80  acts to completely shut off the electric drive system  40 . The shut off of the electric drive system  40  may take the form of setting the maximum torque output of the electric motor assembly to zero or cutting power to the electric drive system  40  completely. The shut off is ended when control module  80  determines that the temperature condition of electric drive system  40  has decreased to a lower reset threshold. Electrical power running through the system and the operation of the electric motor assembly  70  are the primary sources of heat in the electric drive system  40 , and in either the event of system modulation or shut down, reducing the motor torque of the system reduces the amount of heat generated in the system. In the great majority of situations, this reduction in heat generated in electric drive system  40  will allow the system to dissipate heat leading to reduced temperatures in the system and allowing for recovery to normal operation. 
         [0013]    In the exemplary single motor system described above, any motor torque attenuations are desirably accounted for in the overall control strategy of the hybrid drive system. For example, maintaining a desired driveline torque in the event of attenuations of motor torque would require a rebalancing of the torque required from the engine  30 . More particularly, if the motor of motor assembly  70  is operating in a motoring mode and is subjected to torque attenuation, the overall control strategy may adjust engine torque higher in order to maintain driveline torque at a desired level. Similarly, if the motor of motor assembly  70  is operating in a generating mode and is subjected to torque attenuation, the overall control strategy may adjust engine torque lower in order to maintain driveline torque at a desired level. 
         [0014]    Control module  80  may additionally utilize the gathered temperature data for a multitude of uses. Such additional uses may include adaptation of the various temperature set points to various conditions. For example, a particular modulation curve might be used when high environmental (i.e. ambient) temperatures are indicated and a different curve might be used when low environmental temperatures are indicated. When used within a hybrid drive system  10 , the control module could initiate changes in a hybrid control strategy such that lower demands are placed upon the electric drive system  40 . Another exemplary use that the control module  80  might make with the temperature data includes sensor malfunction diagnostics and adaptive controls. If a temperature sensor is determined to be malfunctioning, control module  80  can operate to impose a maximum continuous torque function as a function of electric motor angular velocity in order to decrease the likelihood of thermal damage until the malfunctioning sensor can be replaced. An exemplary embodiment of such a maximum continuous torque function utilized in the case of sensor malfunction is depicted in  FIG. 6 . 
         [0015]      FIG. 2  illustrates an additional embodiment wherein electric drive system  40  may utilize two electric motor assemblies. Power inverter modules  60 A and  60 B are electrically coupled to electric motor assemblies  70 A and  70 B, respectively. Sensors  65 A and  65 B are operable to monitor the temperature of power inverter modules  60 A and  60 B, respectively, and sensors  75 A and  75 B are operable to monitor the temperature of electric motor assemblies  70 A and  70 B, respectively. Sensors  65 A,  65 B,  75 A, and  75 B, collectively, operate to gather temperature data for use by control module  80  in order to calculate an overall temperature condition of electric drive system  40 . Control module  80  utilizes the temperature condition to determine whether modulation of the electric motor assemblies  70 A and  70 B or complete shut down of electric drive system  40  is appropriate. In one particular embodiment, control module  80  is operative to modulate or shut down either electric motor assembly  70 A or electric motor assembly  70 B if the localized temperature readings only justify action upon one portion of system  40 . 
         [0016]    As with the exemplary single motor system previously described, any motor torque attenuations are desirably accounted for in the overall control strategy of the hybrid drive system. And, through such control strategies, the driveline torque is thereby maintained at the desired level. However, in known dual motor systems, for example in a two-mode, compound-split electrically variable transmission such as disclosed in U.S. Pat. No. 5,931,757 which is incorporated herein by reference, the torque attenuations applied to one motor may be accounted for in the other motor torque, the engine torque or a combination thereof Thus, in a hybrid drive system including two motor assemblies, torque attenuation of one motor may be redistributed to the other motor, to the engine or split therebetween in accordance with the overall control strategy of the hybrid drive system. 
         [0017]      FIG. 3  depicts a schematic diagram of an embodiment of a three-phase power inverter module apparatus. Devices operating under AC electrical power frequently operate under three phase power. In this embodiment of electric drive system  40 , three phase AC electric power is used between the power inverter module  60  and electric motor assembly  70 . In order to be operative in three phase electric power, power inverter module  60  utilizes three separate internal electrical circuits  110 ,  120 , and  130 , each operating in a different phase. Each electrical circuit  110 ,  120 , and  130  is paired with a corresponding temperature sensor  115 ,  125 , and  135 . Temperature sensors  115 ,  125 , and  135  take the place of sensor  65  utilized in the embodiment illustrated in  FIG. 1 . At least one temperature sensor  75  continues to be utilized to monitor electric motor assembly  70 . By using a sensor for each individual electrical circuit, the temperature of the power inverter module  60  is more accurately monitored by control module  80 . In one embodiment of the invention, control module  80  will convert the three inputs from temperature sensors  115 ,  125 , and  135  to an operative value to approximate the temperature condition of power inverter module  60 . The operative value may be the maximum reading of the three sensor readings, an average of the three sensor readings, or some other function of the data. In other embodiments, the three inputs can be processed by various algorithms. In addition, control module  80  may operate diagnostic routines (such as comparative, correlative and rationality checks) for the purpose of determining whether any of temperature sensors  115 ,  125 , and  135  are malfunctioning. For example, a preferred method of diagnosing sensor malfunctions is set forth in commonly assigned U.S. patent application Ser. No. 11/669,439 filed on Jan. 31, 2007, which is incorporated herein by reference. The temperature data from malfunctioning sensors will not be used to determine temperature condition of electric drive system  40 . The operative value from sensors  115 ,  125 , and  135  and the readings from sensor  75  are utilized by control module  80  as described in the aforementioned embodiments to determine whether modulation or shut down of system  40  is appropriate. 
         [0018]      FIGS. 4 and 5  are plots used to show temperature condition set points programmed into control module  80  used to operate the thermally protective aspects of the invention. Control module  80 , as aforementioned, receives temperature data from various temperature sensors, preferably with at least one temperature sensor monitoring the motor assembly(s) and one temperature sensor monitoring the inverter module(s). Electric drive system temperature conditions are compared to preprogrammed set points to determine what, if any, torque attenuation control should be imposed upon the electric motor of electric drive system  40 . So long as the temperature condition of electric drive system  40  remains in the normal thermal operating zone, the control module  80  has no modulating effect upon the electric drive system  40 . If the temperature condition of the electric drive system  40  reaches a programmed threshold temperature condition set point, the control module  80  begins to impose a selected reduction of the maximum torque that the electric motor may apply to or receive from the transmission assembly  20 . The algorithm used to impose the selected reduction factor may model a simple linear reduction in the maximum allowable motor torque or may take a more complex form.  FIG. 3  represents an imposition of a linear reduction in allowable torque whereas  FIG. 4  represents an imposition of a parabolic reduction in allowable torque. Different torque limiting curves may be useful depending upon the system usage anticipated. The algorithm may gradually or drastically attenuate the maximum allowable torque of the electric drive system  40  once the threshold temperature condition set point is reached. When the temperature condition of electric drive system  40  gets to some even higher level, the algorithm will have reduced the maximum torque setting to zero. Preferably, should the temperature condition of the electric drive system  40  continue to rise to a programmed shut-off temperature condition set point, the control module  80  may in some embodiments cut all electrical power through inverter module  60  and electric motor assembly  70  to protect the electric drive system  40  and its components from reaching a critical temperature condition or thermal event. 
         [0019]    The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.