Abstract:
In hybrid electric vehicles having increased battery storage capacity and plug-in capability, electric-only operation of significant duration is available. To supplement lubrication for the electric and mechanical components provided in a fluid circuit by an engine-driven mechanical pump, an electric pump is provided in parallel to the mechanical pump. When the electric pump is operating, a diagnostic can be performed to determine system integrity. According to one embodiment, an actual quantity provide to the circuit is determined; an expected quantity is estimated; and a fault is determined when the actual and expected quantities differ by more than a predetermined amount. The fault may indicate a leak or plug in the fluid circuit or a failure of a component in the fluid circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 12/488,842 filed Jun. 22, 2009, now U.S. Pat. No. 8,646,313, issued Feb. 11, 2014, the disclosure of which is hereby incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     The present development relates to supplying oil to lubricate and cool components in a hybrid electric vehicle. 
     BACKGROUND 
     Typical hybrid electric vehicles (HEVs) in widespread use have a limited battery capacity; in such systems the vehicle operates on electric-only operation for limited periods of time. The components requiring lubrication are supplied by a mechanical pump coupled to the internal combustion engine. Thus, in electric-only operation, the mechanical pump does not rotate and supplies no oil to components in the oil circuit. It has been found that the amount of oil in the components is sufficient for such limited periods of electric-only operation. In such HEVs, the amount of electric-only operation is limited, though, by how long the components can survive on the residual lubricant in the system. 
     To further reduce petroleum consumption in HEVs, manufacturers are developing plug-in hybrid electric vehicles (PHEVs). The battery pack on a PHEV has a greater storage capacity and the PHEV is provided with charging capability to charge the battery pack from an electrical grid so that the PHEV derives its power from both the electrical grid and petroleum sources. The duration of electric-only operation in a PHEV is significantly increased in comparison to HEVs with limited battery capacity. The lubrication and cooling needs of power-generating and power-transmitting components in the PHEV are not satisfied by the mechanical pump driven by the internal combustion engine. 
     SUMMARY 
     According to an embodiment of the present disclosure, an electric pump is fluidly coupled to the oil circuit in parallel with the mechanical pump. When the electric pump is operating, a diagnostic can be performed by determining an actual pressure in the circuit and an expected pressure. The fault is determined when the actual and expected pressures differ by more than a predetermined amount. The fault may indicate a leak or plug in the fluid circuit or a failure of a component in the fluid circuit. 
     According to an alternative embodiment, the diagnostic is performed by estimating an actual flow rate, estimating an expected flow rate, and detecting the fault when the actual flow rate differs from the expected flow rate by more than a predetermined amount. 
     An advantage is that the electric pump can be used as a diagnostic to detect faults in the fluid circuit without providing additional sensors to perform such a diagnostic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an exemplary configuration of mechanical components in a hybrid electric vehicle; 
         FIG. 2  is a schematic representation of an exemplary configuration of a fluid circuit for lubricating and cooling components in a hybrid electric vehicle; 
         FIG. 3  is a schematic representation of sensors and actuators coupled to a control unit as part of a hybrid electric vehicle; 
         FIGS. 4 and 5  represent flow charts of methods according to embodiments of the present disclosure; and 
         FIG. 6  shows an example pulse width train to drive an AC motor and the resulting magnetic flux that the pulse width train induces. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     In  FIG. 1 , a schematic of one exemplary mechanical arrangement of components in a HEV is shown. HEV  10  has multiple propulsion sources capable of providing power at the wheels  12 , including: an internal combustion engine  14 , a traction motor  16 , and a generator motor  18 . Internal combustion engine  14  is coupled to a transaxle  19  via a shaft  20 . Shaft  20  drives a mechanical oil pump  22  via gear  24  and pump gear  26 , gear  24  being coupled to shaft  20 . Mechanical oil pump  22  pumps oil through a fluid circuit. The fluid circuit is discussed further in regards to  FIG. 2 . Mechanical oil pump  22  is driven by engine  14 ; thus, when engine  14  is not rotating, mechanical oil pump  22  is not pumping oil. Engine  14  is also coupled to planetary gears  28  of transmission  30 . Transmission  30  includes planetary gears  28  as well as sun gear  32  and ring gear  34 . A generator motor  18  is coupled to sun gear  32  by shaft  38 . Traction motor  16  is coupled by a shaft  40  and gear  42  to ring gear  34  of transmission  30 . Traction motor  16  is coupled to wheels  12  of vehicle  10  via a reduction gear set  44  and  46  and a differential  48 . 
     The HEV embodiment shown in  FIG. 1  represents one non-limiting arrangement. Alternatively, the components of  FIG. 1  are arranged differently and/or the system is comprised of different components. 
     The components enclosed within the dotted line of  FIG. 1  are housed within the transaxle  19 , according to one embodiment. Alternatively, the components shown residing within transaxle  19  may be contained in more than one housing. 
     Referring to  FIG. 2 , a schematic of the lubricant flow system within transaxle  19  is shown. Both the mechanical pump  22  and an electric pump  51  pump lubricant through fluid circuit  50 . Pumps  22  and  51  are arranged in parallel. 
     Mechanical pump  22  has a pressure relief valve  52  to ensure that a maximum system design pressure is not exceeded in fluid circuit  50 . In the branch of fluid circuit  50  having electric pump  51 , there is also a filter  54  and a heat exchanger  56 . In alternative embodiments, filter  54  and heat exchanger  56  are placed in other parts of fluid circuit  50 . Lubricant is provided to generator motor  18  and to transmission  30  before being returned to sump  58 . Parallel to the flow passing through motor  18  and transmission  30  is another branch to heat exchanger  60  and traction motor  16 , which also returns flow to sump  58 . For schematic purposes, sump  58  is shown as a particular container within transaxle  19 . However, sump  58  may comprise the lower portion of transaxle  19 , forming an oil pan of sorts. An oil pickup  62  extending into sump  58  supplies oil to the inlet of pumps  22  and  51 . 
     In  FIG. 2 , lubricant is shown being provided under pressure to generator motor  18 , heat exchanger  60 , traction motor  16 , and transmission  30 . Alternatively and/or additionally, an oil reservoir  64  is provided near the top of transaxle  19 . Reservoir  64  provides drip lubrication to traction motor  16  and generator motor  18 . Within transaxle  19 , rotating components splash lubricant within the casing of transaxle  19  providing yet another way that lubricant is transported within transaxle  19 . The fluid circuit shown in  FIG. 2  is one example of many alternative configurations to provide drip lubrication, pressurized lubrication, spray lubrication, and any combination thereof to the various components within transaxle  19 . Furthermore, the components in  FIG. 2  may be arranged in a different order in the fluid circuit in an alternative embodiment. 
     There are four modes of operation: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                 Mechanical 
                 Electric 
                   
               
               
                 Mode 
                 pump 22 
                 pump 51 
                 Operating condition 
               
               
                   
               
             
             
               
                 1 
                 On 
                 On 
                 Engine 14 on; flow from mechanical  
               
               
                   
                   
                   
                 pump 22 insufficient; supplement with  
               
               
                   
                   
                   
                 electric pump 51 
               
               
                 2 
                 On 
                 Off 
                 Engine 14 on; sufficient flow provided by 
               
               
                   
                   
                   
                 mechanical pump 22 
               
               
                 3 
                 Off 
                 On 
                 Engine 14 off; use electric pump 51 to cool 
               
               
                   
                   
                   
                 and/or lubricate system components 
               
               
                 4 
                 Off 
                 Off 
                 Engine 14 off; duration of pure electric 
               
               
                   
                   
                   
                 operation is short; residual oil from prior 
               
               
                   
                   
                   
                 operation is sufficient to cool and lubricate 
               
               
                   
               
             
          
         
       
     
     In a HEV, whether the internal combustion engine  14  is operating is based on many factors: state of charge of vehicle batteries, driver demand, operating condition, and ambient conditions to name a few. Turning on engine  14  simply for driving mechanical oil pump  22  can constrain HEV operation and negatively impact overall fuel efficiency of the operation, which is one of the disadvantages of the prior art overcome by an embodiment of the present disclosure in which electric pump  51  is provided in parallel with mechanical pump  22 . 
     The terms oil and lubricant have been used interchangeably to describe the fluid within transaxle  19 . In one embodiment the fluid is a transmission fluid. Alternatively, the fluid is any fluid that can lubricate the gears, motor bearings, and shaft bearings as well as carry energy to the heat exchanger to keep the components housed within transaxle  19  sufficiently cool and lubricated. In particular, traction motor  16  and generator motor  18  have two such demands: lubrication of their bearings and cooling of motor windings. Lubricant is also provided to transmission  30  to lubricate both gears and bearings. At a particular vehicle operating condition, cooling of traction motor  16  might be more demanding than any other component in transaxle  19 . At another operating condition, providing lubricant flow to transmission  30  may be most demanding. At even another operating condition, providing lubrication to traction motor  16  bearings may be most demanding. According to an aspect of the present disclosure, the amount of lubricant provided is dictated by the most demanding component at any given operating condition. 
     A schematic representation of electrical connections for a HEV relevant to the present discussion is shown in  FIG. 3 . Power module  66  provides a driving current to electric pump  51 . The control for the driving current is commanded to power module  66  from an electronic control unit (ECU)  68 . Generator motor  18  and traction motor  16  may be provided current from or provide current to power module  66  depending on the operating mode of the HEV system. Power module  66  is coupled to a battery pack (not shown) as an electrical energy source/sink. Electric pump  51  includes a pump driven by an electric motor. In one embodiment, the electric motor is an AC motor, in which case the speed of the motor, and thus the pump, can be inferred, as will be discussed in more detail below. In another embodiment, the electric motor is a DC motor. In such a situation, the electric pump speed can be measured by a speed sensor  74  with the signal from speed sensor  74  provided to ECU  68 . Speed sensor may be a Hall effect sensor proximate a toothed wheel rotating with electric pump  51  or any other speed sensor known to one skilled in the art. 
     According to an embodiment of the present disclosure, operating parameters associated with electric pump  51  can be used to infer flow rate and pressure in the fluid circuit. Such inferred values can be determined whether mechanical pump  22  is operated or not. When both electric pump  51  and mechanical pump  22  are operated, the flow rate provided by mechanical pump  22  is estimated. Because mechanical pump  22  is a positive displacement pump, its estimated output flow rate is based on its rotational speed. Mechanical pump  22  is driven by and coupled to engine  14  via a gear set  24  and  26 . Typically, engine  14  is provided with a toothed wheel  70  and a Hall effect sensor  72 . Sensor  72  provides a signal to ECU  68 , from which engine speed is computed and mechanical pump speed can be computed based on engine speed and a gear ratio of gears  24  and  26 . 
     Electric pump  51 , in one embodiment, is driven by an AC motor. The pump is controlled by applying a pulse width modulated signal, such as  80  shown in  FIG. 4 . The frequency, reciprocal of period, and width of the pulse train  80  applied to windings of an AC motor induces a magnetic flux due to a resulting current flow  82 , thereby causing the AC motor to rotate. The rotational speed of the AC motor is based on the timing and pattern of the applied pulses. The pulses applied to the windings are of longer duration and resulting AC current is higher when a load on the AC motor is high. In such a manner, the torque of the motor can be inferred, or estimated, based on the resulting AC current. 
     A flowchart showing an embodiment of the present disclosure to determine the component having the most demanding lubrication requirement is shown in  FIG. 5 . The algorithm starts in  100  and passes control to block  102  to determine whether the key is on. If not, control passes to block  102  until a positive result is encountered. Upon a positive result in  102 , control passes to block  104  in which a temperature of the windings in a first electric motor, Tw 1 , a temperature of the windings in a second electric motor, Tw 2 , and a powertrain component volumetric flow rate, V, are determined. These three quantities are provided by way of example and not intended to be limiting. For example, in another embodiment, a determination of sufficient lubrication can be based on pressure in place of flow rate. In yet another alternative, the flowchart in  FIG. 4  can be contracted or expanded to include fewer or more decision blocks, examples include: three desired pressures (as demanded by a generator motor, a traction motor, and a transmission); two desired maximum temperatures (traction motor and generator motor) and one minimum flow rate (through transmission) and one maximum temperature (traction motor). 
     Motor winding temperature set points, Tsp 1  and Tsp 2 , may be based on total transaxle  19  losses, preferred motor winding operating temperatures or other criteria. The volumetric flow rate set point, Vsp, may be based on transaxle  19  losses, wear tables, or other criteria. In blocks  106 ,  108 , and  110 , it is determined whether Tw 1  is greater than a first set point temperature, Tsp 1 , whether Tw 2  is greater than a second temperature set point, Tsp 2 , and whether the volumetric flow rate, V, is less than a volumetric flow rate set point, Vsp, respectively. If any one of these conditions returns a positive result indicating insufficient lubricant flow, control is passed to block  112  in which the frequency of the AC current is increased to increase the pump rotational speed. In another alternative, the pump is driven by a DC motor and pulse width to the motor is increased to increase motor rotational speed. Or, in another alternative, the speed of electric pump  51  is increased in block  112  according to any other known manner, such as having multiple, selectable windings in electric pump  51 , which can be switched in and out to affect pump capacity. If negative results are returned in all of blocks  106 ,  108 , and  110 , control passes to block  114  in which it is determined whether temperatures, Tw 1  and Tw 2 , are lower than their respective set point temperatures, Tsp 1  and Tsp 2 , by more than suitable safety factors, Tsf 1  and Tsf 2 , respectively. It is also determined whether the volumetric flow rate exceeds the volumetric flow set point by a suitable safety factor, Vsf. The expressions in block  114  are evaluated using a Boolean “and” operation. Thus, control passes to block  116  only if all the expressions are true; otherwise, control passes to block  104 . A positive result from block  114  passes control to block  116  in which it is determined whether electric pump  51  is on. If it is not, no further decrease is possible and control passes to block  104 . If the electric pump is on, control passes to block  118  in which speed of electric pump  51  is decreased with control returning to block  104 . Depending on the type of electric motor coupled to the pump, the speed is decreased by decreasing the AC frequency, the pulse width, etc. 
     Continuing to refer to  FIG. 5 , when speed of electric pump  51  is increased in  112 , control passes to  120  in which is determined whether the pump speed is greater than or equal to the maximum pump speed. If not, control passes to  104 . If so, control passes to  122  to notify the ECU of the over speed condition. Also in  122 , electric pump speed is set to the maximum speed before returning to block  104 . 
     In other embodiments, a time rate of change quantity is also compared to a threshold to determine whether additional fluid supply is desired. For example, an electric motor that is converting electrical energy into mechanical energy or vice versa can heat up very quickly. Thus, a desired cooling level can be based on both the temperature of the windings as well as a rate of change of the temperature of the windings. Additional refinements, such as use of a PID controller, are obvious to one skilled in the art. 
     In  FIG. 5 , safety factors, Tsf 1 , Tsf 2 , and Vsf, are employed. In alternative embodiments, the safety factors are set to zero. Also in  FIG. 5 , first and second temperature maxima, Tmax 1  and Tmax  2 , are shown. In one embodiment, the same maximum temperature is used to detect overheating in both electric motors with Tmax 1  equal to Tmax 2 . 
     It is desirable to maintain the temperature in generator motor  18  and traction motor  16  below a temperature at which damage can result or maximum operating temperature. The temperature in the motor can be estimated based on a model of energy generation within the motor as well as the energy rejection to the lubricant based on flow to and heat transfer characteristics of the motor. Alternatively, motor temperature can be estimated based on a signal from a sensor in or near the motor. In yet another alternative, the temperature is estimated from a measure of resistance of the windings:
 
 R=R ref[1+α( T−T ref)]
 
     where Rref is the resistance at reference temperature, Tref, and α is the change in resistance per degree temperature change, a material property. Solving for T:
 
 T=T ref+(1/α)( R/R ref−1).
 
     As discussed in regards to  FIG. 5 , control is based on estimating temperature of the motor windings. Alternatively, control could be based on maintaining the resistance in the windings below a threshold. In yet another alternative, a flow rate can be determined which provides the desired cooling. Control can be based on providing that flow rate. 
     Referring to  FIG. 6 , a diagnostic routine starts in block  150 . In  152 , it is determined whether electric pump  51  is operating. If it is not, pump  51  is turned on in  154  prior to proceeding to  156  in which the speed and torque of electric pump  51  are determined. In  158  the speed of mechanical pump  22  is determined. Blocks  156  and  158  can be performed in any order. Control passes to block  160 , in which the total flow rate is determined. Control passes to block  162  in which actual electric pump output pressure is determine based on torque. Control then passes to block  164  in which expected pressure is determined based on flow rate and fluid temperature. Block  164  can be a lookup table or computation based on, e.g., a polynomial equation. Block  166  provides input information for the computation or table lookup in block  164 , providing at least the fluid viscosity as a function of temperature and the loss characteristics of the fluid circuit. Control passes to decision  168  to determine whether the absolute value of the difference in the actual and expected pressures exceeds a predetermined pressure difference. A positive result in decision  168  indicates that a fault is detected and control passes to block  170  in which the fault is indicated by setting a fault code or a light indicating a fault to the operator of the vehicle. Alternatively, specific high and low limits may be set based upon typical failure modes. Otherwise, control passes to block  172 . Rather than run a diagnostic test continuously, in one embodiment, block  172  inserts a delay. In an alternative embodiment, the diagnostic is executed only when electric pump  51  is operating, i.e., the pump isn&#39;t turned on simply for diagnostic purposes. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.