Abstract:
A diagnostic system for controlling an engine low oil pressure indicator in a hybrid electric vehicle includes a powertrain having an engine and an electric traction motor, an oil pressure sensor/sending unit mechanically connected to the engine, an engine speed sensor/sending unit mechanically connected to the engine, a controller having connections to the oil pressure sensor and engine speed sensor, a low oil pressure indicator electrically connected to the controller, a mode selector having modes for “off” and “run/start”, the controller being configured to prevent activation of the low oil pressure indicator when the mode selector is in the “run/start” mode and the engine is not running.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a hybrid electric vehicle (HEV), and specifically a strategy to control a low oil pressure indicator of an HEV&#39;s internal combustion engine (ICE). 
     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. 
     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. 
     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. 
     A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a “powersplit” 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. 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. 
     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 drive-ability. 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. 
     One such area of HEV development is a strategy to indicate diagnose a low oil pressure condition in the HEV&#39;s engine. Control strategies to indicate diagnose low engine oil pressure are known in the prior art for conventional ICE powered vehicles. Typically, a pressure switch/sender unit defaults to a closed position when engine oil pressure drops below some predetermined minimal threshold condition when the vehicle is in a “run” condition. This minimum threshold condition activates a low oil pressure indicator, such as a “low oil pressure” lamp in an instrument cluster of a vehicle or an audible warning or both. The typical, current configuration helps protects the engine by causing the indicator to activate during a system failure, such as when a wire connection is missing wire connection or during a system ground fault, such failure will cause the indicator to activate. This configuration also acts as a de facto “prove-out” or test of the low oil pressure indicator during engine startup, since a typical engine takes time (approximately 300 mSec) to develop enough engine oil pressure to open the switch, thereby deactivating the low oil pressure indicator. 
     Unfortunately, this prior art strategy will not work in an HEV. The HEV&#39;s engine does not run continuously. When the HEV switches to all electric drive or while the vehicle is not in motion, the vehicle is still in “run” mode. However, the low oil pressure indicator would be activated since the oil pressure is not sufficient in the engine to deactivate the indicator. An oil pressure indicator diagnostic strategy for an HEV that activates appropriately needs to be developed. 
     SUMMARY OF INVENTION 
     Accordingly, the present invention provides a diagnostic strategy for controlling a low oil pressure indicator of an internal combustion engine (ICE) for a hybrid electric vehicle (HEV). The HEV has a mode selector, which typically has modes for “off” and “run/start”, and a powertrain with an engine and an electric traction motor. The strategy has an oil pressure sensor/sending unit (oil pressure sensor) and an engine speed sensor/sending unit (engine speed sensor) mechanically connected to the engine. The strategy uses a controller that is connected to the oil pressure sensor and engine speed sensor, and a low oil pressure indicator electrically connected to the controller. An object of the present invention is to prevent activation of the low oil pressure indicator when the mode selector is in the “run/start” mode and the engine is not running, or during engine start up and shut down procedures. 
     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 
     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: 
     FIG. 1 illustrates a general hybrid electric vehicle (HEV) configuration. 
     FIG. 2 illustrates an oil pressure sensing and indicating configuration for a hybrid electric vehicle (HEV) of the present invention. 
     FIG. 3 illustrates the low oil pressure indication diagnostic strategy of the present invention. 
     FIGS. 4A-4B illustrate an alternate embodiment of the low oil pressure indication diagnostic strategy of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention relates to electric vehicles and, more particularly, hybrid electric vehicles (HEVs). FIG. 1 demonstrates just one possible configuration, specifically a parallel/series hybrid electric vehicle (powersplit) configuration. 
     In a basic HEV, a planetary gear set  20  mechanically couples a carrier gear  22  to an engine  24  via a one-way clutch  26 . The planetary gear set  20  also mechanically couples a sun gear  28  to a generator motor  30  and a ring (output) gear  32 . The generator motor  30  also mechanically links to a generator brake  34  and is electrically linked to a battery  36 . A traction motor  38  is mechanically coupled to the ring gear  32  of the planetary gear set  20  via a second gear set  40  and is electrically linked to the battery  36 . The ring gear  32  of the planetary gear set  20  and the traction motor  38  are mechanically coupled to drive wheels  42  via an output shaft  44 . 
     The planetary gear set  20 , splits the engine  24  output energy into a series path from the engine  24  to the generator motor  30  and a parallel path from the engine  24  to the drive wheels  42 . Engine  24  speed can be controlled by varying the split to the series path while maintaining the mechanical connection through the parallel path. The traction motor  38  augments the engine  24  power to the drive wheels  42  on the parallel path through the second gear set  40 . The traction motor  38  also provides the opportunity to use energy directly from the series path, essentially running off power created by the generator motor  30 . This reduces losses associated with converting energy into and out of chemical energy in the battery  36  and allows all engine  24  energy, minus conversion losses, to reach the drive wheels  42 . 
     A vehicle system controller (VSC)  46  controls many components in this HEV configuration by connecting to each component&#39;s controller. An engine control unit (ECU)  48  connects to the engine  24  via a hardwire interface. All vehicle controllers can be physically combined in any combination or can stand as separate units. They are described as separate units here because they each have distinct functionality. The VSC  46  communicates with the ECU  48 , as well as a battery control unit (BCU)  50  and a transaxle management unit (TMU)  52  through a communication network such as a controller area network (CAN)  54 . The BCU  50  connects to the battery  36  via a hardwire interface. The TMU  52  controls the generator motor  30  and traction motor  38  via a hardwire interface. 
     FIG. 2 illustrates an overall oil pressure sensing and indicating configuration for an HEV of the present invention. An operator controlled mode selector  60  activates and deactivates the vehicle. For example, the activation and deactivation of the vehicle can be a “key-on” or “key-off” event. A typical “key-on” event can be a transition of the mode selector  60  from an “off” mode to a “start” or “run” mode. Further, the “key-on” events can further include an “acc” (accessories) mode. From the mode selector  60 , the mode selector  60  output is sent to the VSC  46  and the VSC  46  output is sent to the engine  24  via the ECU  48 . Other controls within the VSC  46  determine the vehicle operating state, including, engine  24  power only, traction motor  38  only, and combined power. For the present invention, an oil pressure sensor  62  and engine speed sensor  68  are added and mechanically connected to the engine  24  to measure engine  24  oil pressure and engine  24  speed respectively. The present invention also contains a controller connecting the oil pressure sensor  62  and the engine speed sensor  68 . The output of the oil pressure sensor  62  and engine speed sensors  68  is sent to an oil pressure indicator logic unit (OPIL)  70 . The OPIL  70  can be integrated into the VSC  46  or can be a stand-alone piece of hardware. For the illustrated embodiments the VSC  46  and OPIL  70  are stand-alone pieces. 
     The OPIL  70  determines whether to send a signal to activate a low oil pressure indicator  64 . The low oil pressure indicator  64  can be electrically connected to the OPIL and can be a conventional “Low oil pressure” lamp in a vehicle instrument cluster or any other means known in the art to indicate that vehicle engine  24  oil pressure is low, such as an audible tone or a combination of a tone and a lamp. 
     FIG. 3 illustrates a first embodiment of the diagnostic strategy of the present invention to determine whether the low oil pressure indicator  64  needs to be activated. This embodiment assumes the engine  24  turns on at each “key on” cycle. The mode selector comprises modes for “off” and “run/start.” The strategy can prevent activation of the low oil pressure indicator  64  when the mode selector is in the “run/start” mode and the engine is not running. 
     The strategy is entered and started at step  100  when the operator controlled mode selector  60  is switched by the operator from “OFF” to “RUN/START” at step  102 . An engine enabled flag is set to DISABLED at step  104 . At step  106 , a first delay timer is reset to its maximum value, by way of example only, of about 1 second. The first delay timer acts to prevent the low oil pressure indicator  64  from activating until a low oil pressure condition has existed for a predetermined time period equal to the maximum timer value. At step  108 , the oil pressure indicator  64  is commanded ON. 
     Next, at step  110 , the OPIL  70  compares the engine  24  oil pressure from the oil pressure sensor  62  to a first predetermined threshold value. By way of example only, the first predetermined threshold value for engine  24  oil pressure can be in the range of about 4.5 to about 7 pounds per square inch (psi). If the oil pressure sensor  62  indicates that the engine  24  oil pressure is not below the first predetermined threshold value, then the strategy moves to step  114  and determines whether the engine enable flag is ENABLED or DISABLED. If the oil pressure is below the first predetermined threshold value, then the strategy moves to step  112  and determines whether the engine enable flag is ENABLED or DISABLED. 
     If at step  114  the engine enabled flag is DISABLED, the engine enabled flag is set to ENABLED at step  118 , the strategy proceeds to step  128 , and at step  128  the strategy sets the oil pressure indicator  64  to OFF. If at step  114  the engine enabled flag is ENABLED, the first delay timer is reset at step  120  and the strategy proceeds to step  128 . At step  128 , the strategy sets the oil pressure indicator  64  to OFF. 
     As stated above, at step  112 , the strategy determines whether the engine enabled flag is set to ENABLED or DISABLED. If the engine enabled flag is set to DISABLED, the strategy moves to step  130  and sets the low oil pressure indicator  64  to ON. If the engine enabled flag is set to ENABLED at step  112 , the strategy proceeds to step  116 . 
     At step  116  the strategy determines whether it has been receiving erroneous data from the engine speed sensor  68 . For example, the strategy determines whether the engine speed sensor  68  data is missing or invalid. If at step  116  the strategy determines the OPIL  70  is receiving erroneous data, the strategy moves to step  126  to monitor and determine whether the first delay timer has expired, meaning the first delay timer has reached zero or some other minimal value. By referring back to the first delay timer, the system ensures that the low oil pressure indicator  64  will only be switched ON if erroneous data is received for a time period greater than that of the first delay timer. If at step  116  the engine speed sensor  68  data is determined to be present and valid, the strategy moves to step  122 , and compares the engine speed to a second predetermined threshold value. By way of example only, the second predetermined threshold for engine speed can be about 500 revolutions per minute (rpm). 
     If at step  122  the engine  24  speed is determined to be above the second predetermined threshold, the strategy moves to step  126  and determines whether the first delay timer has expired. If at step  122  the engine  24  speed is not above the second predetermined threshold at step  122 , the strategy commands the low oil pressure indicator  64  to OFF at step  128 . 
     If at step  126  the first delay timer has not expired, the strategy moves to step  124  and decrements the first delay timer. Put another way, at step  124  the timer value is reduced by a predetermined time. Then, the strategy commands the low oil pressure indicator  64  to OFF at step  128  and proceeds to step  132 . If at step  126  the first delay timer has expired, the strategy commands the oil pressure indicator to ON at step  130  and proceeds to step  132 . 
     At step  132 , the strategy determines the position of the mode selector  60 . If the mode selector  60  is in the RUN/START mode, the strategy returns to step  110 . If the mode selector  60  is OFF or in ACC mode, the strategy exits at step  134 . 
     An alternate embodiment for the diagnostic strategy of the present invention is illustrated in FIG.  4 . This embodiment differs from the first embodiment in that this embodiment does not assume the engine  24  turns on at each “key on” cycle. Additionally, this embodiment checks for proper operation of the oil pressure sensor  62  and engine speed sensor  68 . 
     The strategy is entered at step  200  and transitions to step  202  when the mode selector  60  transitions from OFF or ACC (not shown) to RUN/START. Next, the oil pressure indicator  64  is activated at step  204 ; an oil indicator test timer is reset and activated at step  206 ; and a second timer, an engine  24  speed above second threshold delay timer, is reset at step  208 . By way of example only, the oil indicator test timer can be about 3 seconds and the engine  24  speed above second threshold delay timer can be about 1 second. 
     At step  210 , the strategy determines whether the mode selector  60  is still in the RUN/START mode. If the mode selector  60  is not in RUN/START the strategy exits at step  238 . If the mode selector  60  is in RUN/START mode, the strategy proceeds to step  212 , where the strategy determines whether the oil pressure sensor  62  is functioning properly. 
     If at step  212  the oil pressure sensor  62  is not functioning properly, the low oil pressure indicator  64  is activated at step  224  and the strategy returns to step  210 . In addition to activating the low oil pressure indicator  64  at step  224 , the strategy could also send an error message to the VSC  46 . If at step  212  the oil pressure sensor  62  is functioning properly, the strategy proceeds to step  214 . 
     At step  214 , the strategy compares and determines whether the engine  24  oil pressure is above a first predetermined threshold value. This first predetermined threshold value can be in the range of about 4.5 to about 7 psi. If the engine  24  oil pressure is not above the first predetermined threshold value, the strategy proceeds to step  216 . If the engine  24  oil pressure is above the first predetermined threshold value at step  214 , the strategy proceeds to step  226  where the engine speed above second threshold delay timer is monitored and reset. Then, the strategy moves to step  234  to monitor and determine whether the oil indicator test timer, activated in step  206 , has expired. If the oil indicator test timer has expired at step  234 , the strategy proceeds to step  236  where the low oil pressure indicator  64  is deactivated and the strategy returns to step  210 . If the oil indicator test timer has not expired at step  234 , the strategy skips step  236  and returns to step  210 . 
     If the engine  24  oil pressure is below the first predetermined threshold at step  114 , the strategy determines at step  116  whether the engine speed sensor  68  is functioning properly. If the engine speed sensor  68  is not functioning properly, the low oil pressure indicator  64  is activated at step  228  and the strategy returns to step  210 . Again, in addition to activating the low oil pressure indicator  64  at step  228 , the strategy can also send an error message to the VSC  46 . If, at step  216 , the engine speed sensor  68  is functioning properly, the strategy proceeds to step  218 . 
     At step  218 , the strategy determines whether the engine  24  speed is above a second predetermined threshold value. This second predetermined threshold value can be about 500 rpm. If the engine  24  speed is not above the second predetermined threshold value, the strategy proceeds to step  234 , described more fully above. If the engine  24  speed is above the second predetermined threshold value, the strategy proceeds to step  220  to determine if the engine speed above second threshold delay timer, activated in step  208 , has expired. 
     If at step  220  the engine speed above second threshold delay timer has expired, the low oil pressure indicator  64  is activated at step  230  and the strategy returns to step  210 . If the engine speed above second threshold delay timer has not expired, the strategy proceeds to step  222  where the strategy monitors and determines whether the engine speed above second threshold delay timer is running. 
     If at step  222  the engine speed above second threshold delay timer is not running, the engine speed above second threshold delay timer is started at step  232  and the strategy returns to step  210 . If the engine speed above second threshold delay timer is running, the strategy returns to step  210 . The strategy continues until the mode selector  60  transitions from “RUN” or “START” at which time the strategy ends. 
     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.