Abstract:
A method for controlling torque modification during a gearshift includes modifying transmission input torque during the gearshift using an actuator having slower and faster responses to a request for slow input torque modification, fulfilling the request using the slower response provided the faster response is unable to fulfill the request, and fulfilling the request using the faster response, provided the faster response can provide the requested torque modification.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to controlling torque modulation during a transmission gear change in response to a signal representing slow torque modulation, wherein the torque modulation is performed by a fast actuator. 
         [0003]    2. Description of the Prior Art 
         [0004]    When a transmission upshift is performed, inertia is transmitted through the powertrain to the driven vehicle wheels. But when a transmission downshift is performed, toque produced by the operative vehicle power source must be modulated and vehicle kinetic energy must be absorbed or dissipated. Preferably, in a hybrid electric vehicle kinetic energy is transmitted to the vehicle&#39;s powertrain where it can be regenerated and stored as electric energy in an onboard electric storage battery. 
         [0005]    Use of slow torque modulation for torque reduction during gear shifting will be directed by a command signal toward the slow actuator, i.e., the power source having the slower response time to the signal for torque reduction. Use of the fast torque modulation for torque reduction will be directed by a command signal toward the faster actuator. Potential exists to capture energy from the faster actuator (using the electric machine in a modular hybrid powertrain). But since the slow torque modification is directed toward the slow actuator path, the opportunity to collect this energy may be reduced. 
       SUMMARY OF THE INVENTION 
       [0006]    A method for controlling torque modification during a gearshift includes modifying transmission input torque during the gearshift using an actuator having slower and faster responses to a request for slow input torque modification, fulfilling the request using the slower response provided the faster response is unable to fulfill the request, and fulfilling the request using the faster response, provided the faster response can provide the requested torque modification. 
         [0007]    The method recovers more energy if the fast actuator is an electric machine, thereby compensating for lost energy during other gearshift events. 
         [0008]    The method uses a slow torque modulation request to evaluate whether there is enough capability and authority in the fast actuator to perform the request. If there is sufficient capability/authority, then the fast actuator is used via to provide the request in enough time to satisfy the slow torque modulation request. Since the fast actuator responses faster to the request, sufficient time is available to evaluate this decision and perform the request. 
         [0009]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic diagram showing a modular hybrid electric powertrain for a motor vehicle; 
           [0012]      FIG. 2  contains graphs showing the variation of powertrain parameters during a transmission gearshift in a hybrid electric vehicle; 
           [0013]      FIG. 3  is flow diagram representing an algorithm for controlling transmission gearshift in a hybrid electric vehicle. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]      FIG. 1  illustrates a modular hybrid electric powertrain  10  that includes an internal combustion engine  12 , engine disconnect clutch  14 , electric machine or motor/generator  16 , transmission hydraulic pump  18 , torque converter  20 , torque converter lock-up clutch  22 , transmission gearing  24 , final drive gearing  26 , shafts  28 ,  29 , and driven wheels  30 . A low voltage starter  32 , powered by a low voltage battery  34 , cranks the engine while starting the engine  12  and producing sustained combustion. A high voltage battery  36  powers the electric motor/generator  16 . 
         [0015]    The torque converter  20  is a hydraulic coupling that produces a hydrokinetic drive connection between an impeller, which is driveably connected to the engine  12  when clutch  14  is closed, and a turbine, which is driveably connected to the driven wheels  30 . 
         [0016]    The torque converter lock-up clutch  22  alternately opens and closes a drive connection between the torque converter&#39;s turbine and the shaft  38 . 
         [0017]    A vehicle equipped with this powertrain  10  can produce electric drive and hybrid electric drive and can charge the battery  36  either by regenerative braking, i.e., recovering and converting kinetic energy of the vehicle during a braking event to electric energy that can be stored in battery  36 , or by using the engine to charge battery  36 . 
         [0018]    During regenerative braking, torque is transmitted from the wheels  30  to the electric machine  16 . To recoup most of the kinetic energy using regenerative braking, the torque converter clutch  22  should be kept locked while vehicle speed is slowing. 
         [0019]    The control strategy coordinates operation of the torque converter clutch  22  and the electric machine  16  during a vehicle braking event, whether engine  12  is running or the engine is stopped. If engine  12  is running, its crankshaft is connected to the electric machine  16 ; therefore, the torque converter&#39;s impeller speed can not drop below the engine idle speed. If engine  12  is stopped, the electric machine  16  can be running at speeds lower than the nominal engine idle speed. If the transmission&#39;s hydraulic system line pressure is provided by the mechanical oil pump  18 , the minimal impeller speed should be determined by the minimal pressure that the pump should generate in this case. 
         [0020]    Referring to  FIG. 2 , a downshift is commanded at  40 , and a trigger timer is initiated at  42  and terminated at  44 . 
         [0021]    The variation during the downshift of the extent to which the gearshift is completed is represented by graph  46  (Sft_pct_complete). 
         [0022]    The gearshift phases that occur during the downshift include (i) start shift phase  48  wherein the oncoming transmission control element is prepared for engagement by rapidly pressurizing its hydraulic servo briefly to remove dimensional clearances and then reducing that pressure; (ii) torque transfer phase  50 , wherein torque carried by the offgoing transmission control element is decreased and transferred to the oncoming transmission control element; (iii) ratio change phase  52 , wherein the transmission speed ratio changes; shift end phase  54 , wherein the oncoming control element is fully engaged and pressure in the offgoing element is vented; and gear shift termination phase  56 . 
         [0023]    Graph  58  shows the variation of servo pressure in the oncoming transmission control element during the downshift. 
         [0024]    Graph  60 , representing a slow actuator response to an input torque reduction request, includes a stepwise torque reduction  61  and a ramp reduction when triggered by shift percent complete  46 , followed by another stepwise reduction  62  and a stepwise increase  63  to the original input torque magnitude, when input torque response exceeds the requested input torque  64 . 
         [0025]    Graph  65 , representing a fast actuator response to an input torque reduction request, includes a stepwise torque reduction  66 , followed by a ramped linear increase  67 , and a stepwise increase  68  to the original input torque magnitude, when input torque response exceeds the requested input torque  64 . 
         [0026]    The steps of the algorithm shown in  FIG. 3  are executed by power sources  70  capable of slow response and fast response to a command or request for input torque modification, a vehicle system controller  72 , and a transmission controller  74 . 
         [0027]    At step  76 , controller  72  computes the capability of powertrain  10  to produce a fast modification of input torque, and at step  78  the controller computes the capability of the powertrain to produce a slow modification of input torque. After a gearshift in transmission  24  begins at step  80 , transmission controller  74  triggers a request for a slow torque modification of input torque. 
         [0028]    Slow to fast torque input torque modification is evaluated at step  84 . 
         [0029]    A test is performed at step  86  to determine whether powertrain  10  is able to produce fast input torque modification in response to the request for slow input torque modification produced at step  82 . 
         [0030]    If the result of test  86  is logically negative, a slow actuator is promptly given lead time to react to the request for slow input torque modification so that the slow input torque modification is ready when needed to compensate for inertia effects at step  88 . 
         [0031]    If the result of test  86  is logically positive, a test is performed at step  90  to determine whether a request for fast input torque modification has been triggered by transmission controller  74  at step  92 . The requests triggered at step  82  and  92  allow inertia effects of the gearshift to be compensated by reduction or increase of input torque. A slow actuator requires addition time, whereas a fast actuator does not require additional time. 
         [0032]    If the result of test  90  is negative, control returns to step  90 . 
         [0033]    If the result of test  90  is positive, a fast modification of input torque is produced at step  94 . As illustrated, the step  94  results from the fast modification of input torque or the slow to fast torque modification of input torque. 
         [0034]    When internal combustion engine  12  is producing input torque, adjusting the throttle opening is slow actuation, whereas adjusting ignition timing or spark is fast actuation. In a hybrid electric powertrain, switching the electric machine  16  to operate as a motor produces fast input torque modification in response to a request for increased input torque. Switching the electric machine  16  to operate as a generator produces fast input torque modification in response to a request for input torque reduction. 
         [0035]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.