Patent Publication Number: US-8116932-B2

Title: Auxiliary pump diagnostic systems and methods

Description:
FIELD 
     The present disclosure relates to hybrid vehicles, and more particularly to auxiliary pump diagnostic systems and methods for hybrid transmissions. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     A hybrid vehicle generally includes an engine and a motor generator to selectively provide torque to the transmission. The transmission transmits torque to a driveline. The hybrid configuration may be a belt alternator starter (BAS) system. The BAS system is characterized by a combined motor generator used in place of a standard alternator which is connected to the crankshaft of the engine via an accessory drive belt. The motor generator selectively provides positive torque to assist the engine or negative torque which adds a load to the engine. Assisting the engine draws electrical energy from a charge storage module, typically a battery. Adding load to the engine produces electrical energy which may be used to charge a charge storage module or feed the vehicle&#39;s electrical loads. 
     To reduce fuel consumption, the engine may be selectively stopped when the hybrid vehicle comes to a stop. This will be referred to as an auto-stop. During the auto-stop, the vehicle&#39;s electrical loads are provided by a charge storage module. The engine may restart when a driver lifts his/her foot off the brake pedal. 
     The gear selection of an automatic transmission of a hybrid vehicle is controlled by oil pressure in the transmission. The transmission includes a mechanical oil pump that applies appropriate hydraulic pressure for gear shifting. The transmission&#39;s mechanical oil pump is directly driven by the engine&#39;s crankshaft. When an engine auto-stop is commanded, for example only, when the vehicle stops for a stop light, the mechanical pump is disabled due to lack of power from the engine. An auxiliary transmission oil pump that is driven by an electric motor is enabled during the engine auto-stop. The auxiliary pump supplies oil to the transmission during the auto-stop to maintain a predetermined level of oil pressure in the transmission to maintain clutch pressure. Therefore, when the engine is ready for restart, the transmission is ready to transmit torque to the driveline. The auxiliary pump contributes to a smooth transition of torque to the driveline at engine restart. The auxiliary pump ensures that no undesired clutch slip occurs in the transmission during the engine restart. 
     SUMMARY 
     An auxiliary pump diagnostic system includes a slip determination module and a fault determination module. The slip determination module determines slip of a torque converter based on an engine speed and a transmission input speed. The fault determination module diagnoses a fault in an auxiliary pump based on the slip of the torque converter. 
     In other features, the auxiliary pump diagnostic system includes an enablement module that enables the fault determination module when the slip exceeds a first predetermined value after the engine auto-start is commanded and before a mechanical pump establishes a threshold pressure in the torque converter. The fault determination module diagnoses a fault in the auxiliary pump when a ratio of the slip to an engine speed is below a second predetermined value. 
     A method of diagnosing an auxiliary pump includes determining slip of a torque converter and diagnosing an auxiliary pump based on the slip. The diagnosis starts when the slip exceeds a first predetermined value. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of a hybrid powertrain of a vehicle that includes an auxiliary pump diagnostic system in accordance with the teachings of the present disclosure; 
         FIG. 2  is a functional block diagram of an auxiliary pump diagnostic system in accordance with the teachings of the present disclosure; and 
         FIG. 3  is a flow diagram of a method of diagnosing an auxiliary pump in accordance with the teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term “module” refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     An auxiliary pump diagnostic system in accordance with the teachings of the present disclosure determines slip of a torque converter based on an engine speed and a transmission input speed. The auxiliary pump diagnostic system diagnoses a fault in an auxiliary pump when a ratio of the slip to the engine speed is below a predetermined threshold during engine re-start. 
     Referring now to  FIG. 1 , an exemplary hybrid powertrain  10  includes an engine  12 , an electric machine  14 , a transmission  16 , and a driveline  18 . The electric machine  14  may convert power from the engine  12  into electrical power, which may be stored in a charge storage module  22 . The electric machine  14  may also drive a crankshaft of the engine  12  to propel a vehicle when the engine  12  is not running. When the electric machine  14  is configured as a BAS, the electric machine  14  may be coupled to the engine  12  via a front end accessory drive belt. 
     The transmission  16  receives torque from the engine  12  and transmits the torque to the driveline  18 . The transmission  16  may be an automatic transmission that changes gear ratios automatically. The transmission  16  is hydraulically operated and includes a torque converter  24 , a mechanical pump  26 , an auxiliary pump  28 , friction devices  30 , and a gear set  32 . The torque converter  24  is a type of fluid coupling that is provided between the engine  12  and an input of the transmission  16 . The torque converter  24  generally includes a pump connected to a crankshaft and a turbine connected to the input of the transmission  16 . Auxiliary pump  28  may be a pump either internal or external to the transmission  16  and is driven by an auxiliary pump motor  33 . 
     The torque converter  24  receives torque from the engine  12  and uses hydraulic (oil) pressure in the torque converter  24  to transmit the engine torque to the input of the transmission  16 . The oil pressure is supplied by the mechanical pump  26  when the engine  12  is running or by the auxiliary pump  28  when the engine  12  is shut down. The torque at the input of the transmission  16  is transmitted via the torque converter  22  to the friction devices  30  in the transmission  16  to the gear set  32 , which in turn, transmits torque to the driveline  18 . The friction devices  30  require oil pressure to transmit torque and control which gear ratio is selected in the gear set  32 . 
     For example only, the friction devices  30  may include clutches and/or bands and the gear set may be a planetary gear set. The friction devices  30  may control which components of the gear set are locked to each other, to a housing of the gear set, and/or to the input or the output of the gear set. This controls the gear ratio of the gear set. 
     The mechanical pump  26  is mechanically driven by the engine  12  to provide hydraulic pressure to the torque converter  24 , the friction devices  30  and the gear set  32  when the engine  12  is running. The auxiliary pump  28  is electrically driven by the auxiliary pump motor  33  sourcing power from charge storage module  22 , to supply oil pressure to the torque converter  24 , the friction devices  30  and the gear set  32  during engine auto-stop and engine start. 
     When the engine  12  is running, the mechanical pump  26  which is directly coupled to the engine&#39;s  12  crankshaft provides oil pressure for the transmission  16 . When the engine  12  stops, the mechanical pump  26  is disabled due to lack of power from the engine  12 . The auxiliary pump  28  is enabled to supply oil pressure to the transmission  16  during engine auto-stop. As such, the friction devices  30  (for example only, clutch) and the torque converter  24  remain engaged, ready for engine restart. When the engine  12  restarts, the mechanical pump  26  is enabled. After the engine  12  reaches a certain RPM, the auxiliary pump  28  is deactivated because the mechanical pump  26  is capable of supplying oil pressure to the transmission  16 . 
     The auxiliary pump  28  minimizes pressure dips that may occur when the oil pressure supply is transitioned from the auxiliary pump  28  to the mechanical pump  26 . When the engine  12  stops and the mechanical pump  26  is disabled, a predetermined level of oil pressure is maintained in the hydraulic control circuits (not shown). Therefore, when the mechanical pump  26  is enabled, the mechanical pump  26  can more quickly build the required oil pressure for efficient gear shifting and acceleration without a significant delay. 
     A hybrid engine control module  34  controls the engine  12 , the auxiliary pump motor  33  and the electric machine  14  based on driver inputs  36  and a plurality of sensors (not shown). The hybrid engine control module  34  includes an auxiliary pump diagnostic module  38  that diagnoses the ability of the auxiliary pump  28  to maintain oil pressure during the auto-stop. Diagnostic operation is performed during engine restart. 
     Referring to  FIG. 2 , the auxiliary pump diagnostic module  38  includes an auto stop/start evaluation module  39 , an enablement module  40 , a slip determination module  42 , a driver input evaluation module  44 , and a fault determination module  46 . 
     The auto stop/start evaluation module  39  evaluates engine conditions and determines when an engine auto-start begins and the duration of the auto-stop preceding the auto-start. The auto stop/start evaluation module  39  generates and transmits a signal indicative of the engine auto-start status to the enablement module  40  when the brake pedal  50  is released. The slip determination module  42  calculates slip of the torque converter  24  based on the engine speed and the transmission input speed and generates a signal indicative of the slip value to the enablement module  40 . 
     The enablement module  40  determines whether first enablement conditions are met to trigger a diagnostic timer  48  and whether a second enablement condition is met to activate the fault determination module  46 . The enablement module  40  determines the first and second enablement conditions based on the signals from the auto stop/start evaluation module  39 , the slip determination module  42 , and a vehicle speed sensor  49 . The first enablement conditions are met when the auto-start is commanded, when the duration of an auto-stop preceding the auto-start exceeds a first threshold time, and when the vehicle speed is zero. When the first enablement conditions are met, the enablement module  40  activates the diagnostic timer  48  to start measure the elapsed time after the auto-start is commanded. When the second enablement condition is present, the enablement module  40  enables the fault determination module  46 . For example, the second enablement condition is present when the slip value exceeds a threshold within a predetermined time. For example only, the predetermined time may be one second after the auto-start is commanded. 
     The auxiliary pump diagnostic system  38  in accordance with the teachings of the present disclosure diagnoses the auxiliary pump  28  based on an ability of the torque converter  24  to apply torque to the transmission input immediately after an engine auto-start. The diagnosis is performed during a delay required by the mechanical pump  26  to create pressure in the transmission  16 . Therefore, the auxiliary pump diagnostic system  38  performs diagnosis within the predetermined time period after the auto-start and before the mechanical pump  26  has run long enough (i.e., a threshold time) to pressurize the torque converter  24  and the friction devices  30  on its own. 
     Under normal operation of the torque converter  24 , the output shaft (turbine shaft) of the torque converter  24  rotates slower than the input shaft (pump shaft) of the torque converter  24  by a factor referred to as “slip.” The slip indicates the torque across the torque converter  24 . Slip is defined as the speed difference between the pump shaft and the turbine shaft of the torque converter  24 . The pump shaft is connected to the crankshaft of the engine  12 . The turbine shaft is connected to the transmission input. Therefore, the slip can be defined as follows: 
     
       
         
           
             
               
                 
                   Slip 
                   = 
                   
                     ( 
                     
                       
                         Pump 
                         ⁢ 
                         
                           
                               
                           
                           ⁢ 
                           
                               
                           
                         
                         ⁢ 
                         Speed 
                       
                       - 
                       
                         Turbine 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Speed 
                       
                     
                     ) 
                   
                 
               
             
             
               
                 
                   = 
                   
                     ( 
                     
                       
                         Engine 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Speed 
                       
                       - 
                       
                         Transmission 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Input 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Speed 
                       
                     
                     ) 
                   
                 
               
             
           
         
       
     
     The second enablement condition is present when the slip exceeds a first predetermined value. During an auto-start, the initial acceleration of the crankshaft causes a measurable speed difference between the engine speed and the turbine speed due to the inertia of the turbine elements. The engine speed at this stage of the restart is too low to transmit significant torque to the friction device  30  (e.g., clutch elements). Therefore, this initial check of slip is used to ensure that during the auto-start, the engine speed increases at a rate sufficient to cause an observable inertia based slip signal. This initial check of slip ensures that a failed torque converter will not result in a misdiagnosis of the auxiliary pump  28 . A failed torque converter with an impeller (the element of the torque converter which is driven at engine speed) locked to the turbine will not generate a slip that passes the diagnosis, which will be described below. Therefore, the initial check of the slip immediately after the auto-start ensures that the system acts as expected to accelerate the turbine and the transmission input regardless of oil pressure. 
     When the second enablement condition is met, the enablement module  40  activates the fault determination module  46 . The fault determination module  46  records a sample count. The fault determination module  46  diagnoses the auxiliary pump  28  based on the slip, driver inputs, and engine speeds. The fault determination module  46  records a fail count when the torque converter slip falls below a predetermined percentage of the engine speed. In other words, when a ratio of the slip to the engine speed falls below a second predetermined value and when the driver input evaluation module  44  indicates no changed status of the driver inputs, the fault determination module  46  records a fail count. After a predetermined diagnostic time has elapsed, the fault determination module  46  evaluates the sample counts and the fail counts. When the sample counts reach a threshold and the ratio of fail counts to the sample counts exceeds another threshold, the fault determination module  46  diagnoses a fault in the auxiliary pump  28 . 
     Acceleration of the engine  12  results in an indicated slip across the torque converter  24  (Slip=EngineSpeed−TurbineSpeed). The slip signal is inversely proportional to the magnitude of torque transmitted to the vehicle&#39;s driveline  18 . When the slip is high, this indicates that little of the engine&#39;s torque is transmitted to the vehicle driveline  18 . The high slip condition is indicative of low oil pressure and the concomitant inability of the friction devices  30  to transmit torque. When slip is low, this indicates that the friction devices  30  are directly transferring the engine torque directly to the driveline  18  and consequently must be properly pressurized. When the slip excels a predetermined percentage of the engine speed (for example, a second threshold), it can be determined that the transmission is unable to transmit engine torque due to low oil pressure. Therefore, the ratio of the slip to the engine speed gives an indication of whether the auxiliary pump provided adequate pressure during the auto-stop. 
     The driver input evaluation module  44  communicates with a plurality of driver input devices that include, but are not limited to, a brake pedal  50 , a gear selector  52  and an accelerator pedal  54 . The driver input evaluation module  44  identifies conditions that may affect the slip of the torque converter  24  during engine start, which may cause a false diagnosis. 
     In some situations, a changed status of the driver input devices may result in a signal profile (or slip profile) that corresponds to a failed pump. For example only, a false diagnosis may occur when the gear selector  52  is shifted (particularly to a Neutral position) during diagnosis. In this situation, the transmission  16  may be commanded to transmit less torque or no torque to the driveline  18 . Therefore, the ratio of the slip to the engine speed may not exceed the second predetermined value, resulting in a slip profile that corresponds to a failed pump. 
     A false diagnosis may occur when the vehicle is directed downhill during engine auto-start and the vehicle may accelerate with little torque transmitted across the torque converter. In this situation, the engine speed increases relatively fast with little torque transmitted from the engine  12  to the transmission  16 . The ratio of the slip to the engine speed may not exceed the second predetermined value during diagnosis, resulting in a slip profile that corresponds to a failed auxiliary pump. 
     Therefore, the driver input evaluation module  44  evaluates the status of the driver input devices and determines whether the driver input devices are changed during diagnosis to adversely affect an accurate diagnosis. The driver input evaluation module  44  also monitors the vehicle speed. Upon identifying a situation that may affect an accurate diagnosis (for example only, changed status of driver input devices or vehicle speed increasing too fast), the driver input evaluation module  44  sends a signal to the enablement module  40 . The signal from the driver input evaluation module  44  indicates that vehicle conditions are incorrect for accurate diagnosis. In response to the signal from the driver input evaluation module  44 , the enablement module  40  aborts the diagnosis and discards the diagnostic data. If no signal indicative of incorrect vehicle conditions is received from the driver input evaluation module  44 , the enablement module  40  activates the fault determination module  46  to continue to diagnose the operation of the auxiliary pump  28 . 
     Referring now to  FIG. 3 , a method  80  of diagnosing an auxiliary pump starts in step  82 . Step  82  is executed at a periodic rate sufficient to satisfy the diagnostic&#39;s accuracy requirements. For exemplary purposes, this rate may be every 25 milliseconds. The auto stop/start evaluation module  39  determines when and whether an auto-start trigger has been issued in step  84 . When an auto-start trigger is not commanded in step  84 , the method  80  proceeds to step  87 , which will be described below. When an auto-start trigger is commanded in step  84 , the method  80  proceeds to step  85 . The path from step  84  to  85  will only be taken once per auto start event. 
     In step  86 , the enablement module  40  determines whether the first enablement conditions are met to trigger the diagnostic timer  48 . The first enablement conditions are met when vehicle speed is zero and when the auto stop preceding the auto start was active for a period of time greater than a first threshold K 1 . These requirements ensure that the auxiliary pump  28  has been enabled long enough to merit diagnosis. If both conditions are valid, a diagnostic timer  48  is initialized, along with additional variables used to monitor the diagnostic progress in step  88 . If the enablement conditions are not met in step  85 , the method  80  proceeds to step  104  and ends. 
     In step  87 , a check is made to determine if the diagnostic has been enabled in step  86 . If the diagnostic has been enabled in step  87 , the driver input evaluation module  44  determines whether the driver input status has changed or the vehicle speed increases at a rate faster than a threshold rate K 2  during diagnosis in step  88 . If the driver input status is not changed and the vehicle speed does not increase at a rate faster than the threshold rate K 2 , the diagnostic timer  48  increments the diagnostic time and the slip determination module  42  determines a slip of the torque converter (“TCC_Slip”) in step  90 . Otherwise, the enablement module  40  aborts the diagnosis and resets the diagnostic data in step  102 . 
     The enablement module  40  determines whether the TCC_Slip has been high (i.e., whether the TCC_Slip has been exceeding a third threshold K 3 ) in step  91 . If the TCC_Slip has been high in step  91 , the second enablement condition is met. Therefore, the fault determination module  46  is activated to increment sample counts in step  96 . If the TCC_Slip has not been high in step  91 , the enablement module  40  determines whether the TCC_Slip exceeds the third threshold K 3  in step  92 . If TCC_Slip exceeds the third threshold K 3  in step  92 , the enablement module  40  activates the fault determination module  46  and updates the diagnostic variables in step  94 . The method  80  then proceeds to step  88  where the diagnostic timer  48  is checked. If the diagnostic timer  48  records a diagnostic time that is less than the fifth threshold K 5 , the method  80  proceeds to step  104 . If the diagnostic timer is greater than the fifth threshold K 5  in step  88 , the fault determination module  46  evaluates the diagnostic data in step  100 . 
     Returning to step  91 , when the TCC_Slip has been high in step  91 , all conditions to enable diagnosis of auxiliary pump  28  have been satisfied. In step  96 , the fault determination module  46  increments the sample counts in step  96 . Each sample count represents a check of the slip criteria (i.e., all enablement conditions are met for an accurate diagnosis). Step  96  proceeds to step  97 . The fault determination module  46  determines whether a ratio of the slip to the engine speed is below a fourth threshold K 4  in step  97 . If the ratio of the slip to the engine speed is below the fourth threshold K 4 , the fault determination module  46  increments a fail count in step  99 . If the ratio of the slip to the engine speed is above the fourth threshold K 4  in step  97 , the method  80  proceeds to step  88 . As previously set forth, when the diagnostic time exceeds the fifth threshold K 5  in step  88 , the fault determination module  46  evaluates the logged diagnostic data to determine whether the auxiliary pump fails in step  100 . The logged diagnostic data include the logged sample counts and fail counts. 
     The fault determination module  46  records and evaluates data regarding sample counts and fail counts. If the sample counts are greater than a sixth threshold and the ratio of fail counts to the sample counts exceeds a seventh threshold, the fault determination module  46  diagnoses a fault in the auxiliary pump. Otherwise, the diagnostic is passed. The method  80  then proceeds to step  102  to reset the diagnostic variables in preparation for the next auto start event. The method  80  ends in step  104 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.