Abstract:
In a powertrain for motor vehicle that includes an engine, an electric machine able to function alternately as a motor and a generator, and a transmission whose input is driveably connected to the engine and the electric machine, a method for controlling transmission input torque during an upshift including using the engine to produce torque transmitted to the transmission input, during the ratio change phase of the upshift, operating the electric machine as a generator, and during the ratio change phase of the upshift, controlling a net torque transmitted to the transmission input by using the engine to drive the transmission and the electric machine concurrently.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a powertrain for a hybrid electric vehicle (HEV), and, in particular to a method for performing transmission input torque modulation during a change to a higher gear. 
         [0003]    2. Description of the Prior Art 
         [0004]    In a conventional vehicle equipped with a transmission that produces step changes among gear ratios, the driver can experience driveline disturbances during a gear shift. The driveline disturbances occur due to the acceleration and deceleration of the engine and transmission component inertias, which produce an inertial torque during the gear shift. In the case of an upshift, the transmission output torque increases during the ratio change phase of the gear shift as a result of the engine speed changing. 
         [0005]    This output torque disturbance is directly felt by occupants of the vehicle and affects shift quality. The level of output shaft torque disturbance increases with the speed of the upshift since engine deceleration is greater with faster gear shifts. By reducing engine torque produced during the upshift, inertial torque can be offset and the output shaft torque increase can be minimized, thereby improving shift quality. The method of reducing engine torque produced during the upshift is referred to as “input torque modulation” control. 
         [0006]    In the case of a downshift, the transmission output torque decreases during the ratio change phase as the engine and transmission components accelerate to the synchronous speed for the lower gear. Moreover, during the torque transfer phase of the downshift, the transmission output torque can spike near the completion of the downshift as the engine accelerates. The drop in output torque during the ratio change is directly felt by the vehicle occupants and can give the sense of an acceleration discontinuity as the downshift is performed. The output torque spike at the end of the downshift can affect shift quality and produce a feeling of a rough shift. Furthermore, the level of output shaft torque drop and spike near the end of the downshift will increase in proportion to speed of the downshift. 
         [0007]    By using input torque modulation, the engine combustion torque can be reduced near the end of the downshift in order to reduce the engine&#39;s acceleration as the shift ends. As a result, the transmission output torque spike can be minimized and avoided, thereby reducing the shift disturbance. 
         [0008]    In conventional vehicle applications, limitations and problems with input torque modulation during gear shifts include limited engine torque reduction authority due to constraints, such as emissions; delayed engine torque response to torque modulation requests, further degrading shift quality; and poor fuel efficiency, since spark retardation is commonly used for achieving torque modulation requests. 
       SUMMARY OF THE INVENTION 
       [0009]    In a powertrain for motor vehicle that includes an engine, an electric machine able to function alternately as a motor and a generator, and a transmission whose input is driveably connected to the engine and the electric machine, a method for controlling transmission input torque during an upshift including using the engine to produce torque transmitted to the transmission input, during the ratio change phase of the upshift, operating the electric machine as a generator, and during an ratio change phase of the upshift, controlling a net torque transmitted to the transmission input by using the engine to drive the transmission and the electric machine concurrently. The engine torque and torque required to drive the electric machine can be varied during the ratio change phase. 
         [0010]    During a transmission shift event, the electric machine is controlled to produce accurately a transmission input torque modulation request. By taking advantage of the electric machine&#39;s capability, output shaft torque disturbances are reduced and optimum shift quality is achieved. 
         [0011]    The transmission input torque modulation control strategy can be applied to HEV powertrains including rear wheel drive, front wheel drive and all wheel drive configurations, full HEV, mild HEV having at least one electric machine at the transmission input. Furthermore, this control strategy is applicable to conventional automatic transmission, dual clutch powershift transmissions, and converterless automatic transmissions. 
         [0012]    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 
         [0013]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a schematic diagram showing an automotive vehicle powertrain for a hybrid electric vehicle; 
           [0015]      FIG. 2  is a schematic diagram showing propulsion and power flow of the vehicle powertrain of  FIG. 1 ; 
           [0016]      FIG. 3  is a schematic diagram showing vectors representing torque transmission among components of the powertrain operating in mode A; 
           [0017]      FIG. 4  is a schematic diagram showing vectors representing torque transmission among components of the powertrain operating in mode B; 
           [0018]      FIGS. 5A-5D  illustrate the change of powertrain variables during a transmission upshift performed with input torque modulation; 
           [0019]      FIGS. 6A-6D  illustrate the change of powertrain variables during a transmission downshift performed with input torque modulation; 
           [0020]      FIG. 7  is a logic flow diagram of an algorithm for providing input torque modulation transmission control in the HEV powertrain of  FIG. 1 ; 
           [0021]      FIG. 8  is a logic flow diagram of an algorithm for selecting the operating mode of the powertrain of  FIG. 1  during input torque modulation control; and 
           [0022]      FIG. 9  is a schematic diagram showing vectors representing torque transmission among components of the powertrain operating in mode C. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Referring first to  FIGS. 1 and 2 , the powertrain  10  configuration includes a first power source such as an internal combustion engine  12 , a diesel engine or a gasoline engine; a power transmission  14  driveably for producing multiple forward and reverse gear ratios, such as a wet-clutch powershift transmission; an electric machine  16  driveably connected to the engine crankshaft and transmission input  18 , such as a crankshaft-integrated starter/generator (CISG) for providing starter/generator capability; and an additional electric machine  20  driveably connected to a rear axle differential mechanism  36 , such as an electric rear axle drive (ERAD), for providing additional propulsion capability in either an electric drive or hybrid drive mode. The transmission output  24  is connected through a final drive unit and differential mechanism  26  to the front axles  28 ,  30 , which drive the front wheels  32 ,  33 , respectively. ERAD  20  drives the rear wheels  34 ,  35  through ERAD gearing  48 , a differential mechanism  36 , rear axles  22 ,  23  and wheels  34 ,  35 . 
         [0024]    The powertrain  10  comprises a first power path driveably connected to the load that includes CISG  16 , transmission  14 , final drive unit  26 , axles  28 ,  30  and the wheels  32 ,  33 . A gear of the transmission must be engaged between input  18  and output  24  and the input clutch  38  or  39  that is associated with the engaged gear must be engaged to complete a drive path between CISG  16  and the vehicle wheels  32 ,  33 . Powertrain  10  also comprises a second power path driveably connected to the load that includes ERAD  20 , ERAD gearing  48 , a differential mechanism  36 , rear axles  22 ,  23  and wheels  34 ,  35 . 
         [0025]    An electronic engine control module (ECM)  24  controls operation of engine  12 . An electronic transmission control module (TCM)  27  controls operation of transmission  14  and the input clutches  38 ,  39 . An integrated starter controller (ISC)  40  controls operation of CISG  16 , ERAD  20  and the system for charging an electric storage battery  42 , which is electrically coupled to the electric machines  16 ,  20 . 
         [0026]      FIG. 2  shows the power and energy flow paths from the power sources  12 ,  16 ,  20  to the load at the vehicle wheels  32 - 35 . Power produced by engine  12  and power produced by CISG  16  are combined at  44  and transmitted to the transmission input  18 . Electric power produced by both electric machines  16 ,  20  is combinable at  46  for charging the battery  42 , or is transmitted from the battery to the electric machines. Mechanical power produced by ERAD  20  is transmitted through ERAD gearing  48  to the load at the rear wheels  34 ,  35  through the rear final drive  36 . 
         [0027]    In a hybrid electric vehicle application in which a fixed-ratio transmission is used and at least one electric machine is coupled to the engine crankshaft  18  to provide engine start/stop capability such as a crankshaft integrated starter/generator (CISG)  16 , enhanced input torque modulation can be provided during transmission shifts in a superior method compared to that of a conventional input torque modulation strategy. 
         [0028]    As shown in  FIGS. 3 and 4 , operating modes of the powertrain  10  are used to provide transmission input torque modulation during transmission shift events. Depending on the type of shift event, i.e., an upshift or downshift, level of torque modulation request, CISG operating conditions, battery conditions, and other factors, the appropriate powertrain operating mode will be used to provide the desired input torque modulation request.  FIG. 3  is a schematic diagram of the powertrain  10  showing vectors representing torque transmission among components during operating mode A, in which the CISG  16  reduces transmission output torque during an upshift. 
         [0029]      FIGS. 5A-5D  illustrate the change of certain powertrain variables during a transmission upshift in which input torque modulation is provided by the CISG  16  using operating mode A, whose power flow among powertrain components is illustrated in  FIG. 3 . In operating mode A, CISG  16  operates as an electric generator to provide input torque modulation and to reduce the transmission output torque disturbance  50  that would result if no torque modulation were being performed. CISG is operative for this purpose provided that the CISG is available, i.e., its current temperature is less than its temperature limit, its speed is less than its operational speed limit, etc., and the battery state of charge (SOC) is below the maximum allowable limit. 
         [0030]    In operating mode A, CISG  16  is driven by engine  12 , thereby reducing the net torque  52  transmitted by crankshaft  18  to the input of transmission  14  during the ratio change phase  54  of the upshift, i.e., while the change gear ratio change  56  is occurring following the torque transfer phase  55 . The negative CISG torque  58  which is controlled to provide input torque modulation during the shift is shown in  FIG. 5D . As shown in  FIG. 5C , excess torque  60  produced by engine  12  during the ratio change phase is recovered and converted into electrical energy that is stored by the battery  42 , while achieving the requested input torque modulation and providing optimum shift quality.  FIG. 5A  illustrates the difference  62  between the magnitude of torque  64  at the transmission output shaft  24  with CISG  16  providing input torque modulation for optimum shift quality and the output torque  50  with no input torque modulation provided. 
         [0031]    Delays in crankshaft torque reduction can be avoided by taking advantage of the responsiveness of CISG  16  thus leading to accurate input torque modulation levels. Operating mode A can also be used with both CISG  16  and engine  12  reducing the net crankshaft torque to meet the requested input torque modulation level. This is useful in the case where the CISG may not be fully available for input torque modulation or the battery SOC is near its maximum limit. 
         [0032]      FIGS. 6A-6D  illustrate the change of certain powertrain variables during a transmission downshift in which input torque modulation is provided by the CISG  16  using both operating modes A and B , whose power flow among powertrain components is illustrated in  FIGS. 3 and 4 , respectively. 
         [0033]    As  FIG. 6A  shows, during the ratio change or ratio change phase  54  of the downshift, powertrain  10  is placed in operating mode B as shown in  FIG. 4 , wherein CISG  16  operates as an electric motor to increase the transmission output torque to a level  68  rather than a output torque drop  76  that would result if no torque modulation were being performed. During the ratio change phase  54  of the downshift, CISG torque  70  supplements the engine torque  72  so that the net crankshaft torque  74  is increased to output shaft torque level  68  in order to offset the transmission output torque decrease  76 , which would occur without torque modulation. This would provide acceleration continuity during the downshift and improved shift performance. 
         [0034]    Operating mode B is used provided that the CISG  16  is available, i.e., its current temperature is less than its temperature limit, its speed is less than its operational speed limit, and the battery state of charge (SOC) is greater than the minimum allowable limit. This CISG capability is unique to that of an HEV since the CISG can be used to offset the output torque drop  76  so that the driver can sense acceleration continuity during the downshift. 
         [0035]    During the torque transfer phase  55  near the completion of the downshift, as shown in  FIGS. 6A and 6C , powertrain  10  functions in operating mode A with CISG  16  operating as a electric generator in order to provide input torque modulation. As shown in  FIGS. 6C and 6D , CISG  16  is controlled to a negative torque  78  near the end of the downshift during the torque transfer phase to provide torque modulation so that the net crankshaft torque  74  is reduced in order to minimize or eliminate the transmission output torque spike  80 , which would normally occur without the CISG providing torque modulation. This excess crankshaft torque  82  produced by the engine  12  is converted to electrical energy and stored by the battery  42 , while achieving the requested input torque modulation and providing optimum shift quality. Moreover, by taking advantage of the responsiveness of CISG  16 , delays in crankshaft torque reduction can be avoided thus leading to accurate input torque modulation control during the downshift. 
         [0036]      FIG. 7  shows the steps of an algorithm for providing input torque modulation transmission control of the HEV powertrain of  FIG. 1 . After execution of the algorithm is started and the operating conditions of powertrain  10  are assessed at step  90 , a test is performed at step  92  to determine whether a gear ratio change of the transmission  14  has been requested by a transmission controller acting in response to vehicle parameters that include without limitation engine throttle position, accelerator pedal position, vehicle speed, engine speed, the position of a manually operated gear selector, and a schedule of the preferred gear ratios related to the vehicle parameters. 
         [0037]    If the result of test  92  is logically positive, control advances to step  94  where a test is performed to determine whether shift input torque modulation is requested by the controller. If the result of either test  92  or  94  is logically negative, control returns to step  90 . But if the result of test  94  is positive, the magnitude of desired input torque modulation is determined at step  96 . The desired magnitude of input torque modulation is determined based on the shift event progress. For example, at the beginning of the ratio change phase of an upshift, the desired magnitude will ramp from zero to a negative steady-state level as the ratio change continues and will ramp back to zero as the ratio change phase is completed. 
         [0038]    At step  98 , the operating mode of powertrain  10  is selected in accordance with the algorithm of  FIG. 8  upon reference to current operating parameters and the desired magnitude of input torque modulation. 
         [0039]    At step  100 , powertrain  10  is placed in the desired operating mode selected by algorithm of  FIG. 8  in order to provide the desired input torque modulation during the shift event. 
         [0040]    Referring now to the algorithm for selecting the desired operating mode shown in  FIG. 8 , a test is performed at step  102  to determine whether the CISG temperature is less than a high temperature reference. 
         [0041]    If the result of test  102  is positive, a test is performed at step  104  to determine whether the speed of CISG  16  is less than a reference speed representing the maximum allowable operating speed of the CISG. 
         [0042]    If the result of test  104  is positive, a test is performed at step  106  to determine whether the magnitude of a request for transmission input torque modulation is less than a reference torque limit representing the current maximum torque capability of CISG  16 . 
         [0043]    If the result of any of tests  102 ,  104  or  106  is negative, control advances to step  108 , where powertrain  10  is placed in operating mode C, in which torque produced by engine  12  alone is transmitted to transmission output  24  without CISG torque affecting any change in torque carried on crankshaft  18  to the transmission input and CISG  16  neither produces or draws power. Operating mode C, shown in  FIG. 9 , is that of a conventional vehicle and the engine torque will be reduced to provide the desired level of input torque modulation since the CISG cannot be used. 
         [0044]    If the result of test  106  is positive, a test is performed at step  110  to determine whether the desired magnitude of transmission input torque modulation is negative. If the result of test  110  is positive indicating that the desired input torque modulation level is negative and the crankshaft torque is to be reduced, a test is performed at step  112  to determine whether the battery SOC is less than a maximum allowable SOC reference. 
         [0045]    If the result of test  112  is positive indicating that the battery SOC can be further increased as the CISG is operated as an electric generator, at step  114  operating mode A is selected, indicating that CISG  16  is available for input torque modulation by converting power produced by engine  12  into electrical energy to be stored by the battery during an upshift or downshift while achieving the desired input torque modulation level. 
         [0046]    If the result of any of test  112  is negative indicating that the battery SOC cannot be further increased, control advances to step  108 , where powertrain  10  is placed in operating mode C, in which torque produced by engine  12  alone is transmitted to transmission output  24  without CISG torque affecting any change in torque carried on crankshaft  18  to the transmission input and CISG  16  neither produces or draws power. 
         [0047]    If the result of test  110  is negative indicating that the desired input torque modulation level is positive and the crankshaft torque is to be increased, a test is performed at step  116  to determine whether the battery SOC is less than a minimum SOC before operating the CISG as an electric motor and discharging the battery. 
         [0048]    If the result of test  116  is positive, at step  118  operating mode B is selected, indicating that CISG  16  is available for torque modulation by supplementing power produced by engine  12  during a downshift. 
         [0049]    If the result of test  116  is negative, control advances to step  108 , where powertrain  10  is placed in operating mode C, in which torque produced by engine  12  alone is transmitted to transmission output  24  without CISG torque affecting any change in torque carried on crankshaft  18 . 
         [0050]    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.