Abstract:
A vehicle powertrain has an engine coupled to an electronically-controlled automatic transmission. A method for controlling the vehicle powertrain during a transmission shift from a neutral gear to a drive gear detects a change in a signal indicative of a desired transmission gear change from a neutral gear to a drive gear. An engine idle speed is reduced by a predetermined RPM in response to the change in the signal. The transmission is shifted from the neutral gear into the drive gear upon the engine idle speed being reduced by the predetermined RPM.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to controlling a vehicle powertrain, and, more particularly, to a system and method in which engine and transmission control segments communicate in order to control torque in the vehicle powertrain.  
       BACKGROUND  
       [0002]     In motor vehicles it is desirable to control or reduce particular noises and vibrations created in the vehicle powertrain. One source of noise is caused by the collective lash between components in the vehicle driveline. As the vehicle is changed from a neutral gear to a drive gear, the transmission applies torque to the driveline which causes its components to move and take-up the collective lash. As the components move, the driveline emits a noise which is commonly referred to as driveline clunk. As engine RPM increases, as is often the case when an engine is idling after a cold start, the driveline clunk becomes increasingly annoying. However, the increased engine RPM is desirable to increase the heating of an exhaust catalyst connected to the engine.  
       SUMMARY OF THE INVENTION  
       [0003]     Accordingly, one aspect of the present invention is to provide a system and method for providing an elevated cold engine idle speed while also minimizing driveline clunk.  
         [0004]     In accordance with these aspects, a vehicle powertrain is provided having an engine coupled to an electronically-controlled automatic transmission. A method for controlling the vehicle powertrain during a transmission shift from a neutral gear to a drive gear detects a change in a signal indicative of a desired transmission gear change from a neutral gear to a drive gear. An engine idle speed is reduced by a predetermined RPM in response to the change in the signal. The transmission is shifted from the neutral gear into the drive gear upon the engine idle speed being reduced by the predetermined RPM.  
         [0005]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a block diagram of a powertrain control system; and  
         [0007]      FIG. 2  is a timing diagram illustrating operation of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]     Turning now to  FIG. 1 , a block diagram of a vehicle powertrain  1  is shown. An engine  22  has a crankshaft  32 , which is connected to one side of a viscous coupling  26 . The other side of the viscous coupling  26  provides input torque TIN to an input shaft  34  of electronically controlled transmission  28 . The transmission  28  provides output torque T OUT  at output shaft  36 , which is connected to the driveshaft and axles (not shown) as is known in the art. Transmission  28  also has at least one gear engagement control input  38  for engaging a drive gear and a neutral gear in the transmission. Engine  22  has an idle air control valve  20  for providing combustion air to the engine  22 . The idle air control valve  20  is controlled by a powertrain control module (PCM)  10 . A spark angle control line  21  from the PCM  10  controls the ignition angle of engine  21 . Exhaust gas from engine  22  is routed through a catalyst  17  to reduce undesirable exhaust emissions.  
         [0009]     The PCM  10  has an engine segment  12  and a transmission segment  14 . The two segments communicate via a communications block  16 . In one aspect, each segment  12 ,  14  may have its own microprocessor, with the communications block  16  comprising a dual-port RAM or communication bus between the segments  12 ,  14 . In another aspect, the segments  12 ,  14  may be physically separated controllers, with the communications block  16  comprising a network between them. In yet another aspect, PCM  10  may have a single microprocessor, with segments  12 ,  14  being implemented in software with the communications block  16  comprising memory locations.  
         [0010]     Each segment  12 ,  14  executes instructions from its respective memory  12 ′,  14 ′. The instructions provide operation in accordance with the method of the invention as described below. Engine segment  12  receives a throttle signal from throttle pedal position sensor  18  and also receives a crankshaft signal from a crankshaft sensor  24 . A catalyst temperature signal  15  may be used to provide engine segment  12  with catalyst temperature data. Alternatively, the engine segment  12  may estimate the catalyst  17  temperature. Transmission segment  14  receives a drive/neutral (D/N) signal from a gear selector switch  30 . Alternatively, the transmission segment  14  may receive the D/N signal as a message from a vehicle network arrangement. When the transmission  28  is in neutral, the output torque T OUT  is approximately zero. Conversely, when the transmission  28  is in a drive gear, the output torque T OUT  is a multiple of input torque T IN .  
         [0011]     Turning to  FIG. 2 , operation of the invention is shown in a time-correlated format wherein the x-axis of each graph represents time. The y-axis of each graph represents the quantity stated in each graph&#39;s y-axis label. Graph  40  shows engine crankshaft 32 RPM during a typical cold engine start. The engine module  12  determines crankshaft RPM from the crankshaft sensor  24  as is known in the art. Beginning at time T 0 , the engine RPM is zero and increases as the engine is started. A short time later, after the engine has fired, the engine RPM is sufficient to declare that a start-to-run transfer  42  has occurred and the engine is running. When the engine is started in a cold condition the engine module  12  sets the engine idle speed greater than a typical idle speed  44 . This elevated idle speed is desirable to increase the rate of heat accumulation in the exhaust catalyst  17 . However, the elevated idle speed is undesirable when shifting the transmission  28  from a neutral gear to a drive gear since it increases the likelihood of driveline clunk.  
         [0012]     Graph  60  depicts a D/N signal. At time  62 , the D/N signal indicates to the PCM  10  that the gear selector switch  30  has been changed from a neutral gear to a drive gear. In response to this indication, the engine control segment  12  reduces the desired idle speed as shown by sloped segment  72  in graph  70 . Graph  80  represents motion of the idle air control valve  20 . After time  62 , the idle air control valve  20  begins closing to reduce the engine idle speed  82  in response to the desired idle speed reduction at sloped segment  72 . Additionally, the engine segment  12  may retard the spark angle via spark angle control line  21  to reduce engine RPM. Reducing the spark angle to reduce engine RPM may provide a faster response than reducing engine RPM via the idle air control valve  20 .  
         [0013]     Once the engine RPM decreases by a predetermined RPM  46  from the RPM at time  62 , the transmission control segment  14  sends a gear engagement signal to the transmission via gear engagement control  38 . The predetermined RPM  46  may be dynamically adjusted depending on factors such as the engine coolant temperature, transmission oil temperature, ambient air temperature, catalyst temperature, or time since engine start  42 . By decreasing the engine RPM by the predetermined RPM  46  as described, the transmission  28  may shift into a drive gear without generating an undesirable amount of driveline clunk.  
         [0014]     The transmission  28  begins shifting into a drive gear upon receiving the gear engagement signal. After a shift delay period expires at time  92 , the transmission control segment  14  may send an impending shift signal  90  to the engine control segment  12  via communication block  16 . The shift delay period accounts for a time lag between the transmission receiving the gear engagement signal and the transmission beginning to shift into a drive gear. The impending shift signal indicates that the transmission gear engagement is imminent and the torque load on the engine will therefore increase. Upon receiving the impending shift signal  90 , the engine control segment  12  increases the IAC position  84  to increase the engine output torque. Advancing the ignition timing of the engine may also be used to increase engine torque. The engine torque increase is resultantly coordinated with the transmission torque increase, thereby minimizing engine RPM transients during the gear engagement.  
         [0015]     The operation described above may be further enhanced by providing an enable period  52 . The enable period may be maintained by either the engine or transmission control segment and ensures the above-described operation sequence only activates during the period following a cold start of the engine. An enable period  52  is shown in graph  50 . The enable period may further be a function of the catalyst temperature.  
         [0016]     A fail-safe timer  100  may also be provided within the PCM  12 . The fail-safe timer operates to allow the shift to occur within a predetermined time after the D/N signal is received at time  62  in the event the engine RPM does not decrease by a predetermined RPM  46 . Upon expiration  102  of the fail-safe timer, the transmission control segment  14  will shift the transmission into gear regardless of whether the engine RPM has decreased by predetermined RPM  46 .  
         [0017]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.