Abstract:
A method of managing tip-in bump in an automatic transmission includes detecting a set of conditions indicative of an impending throttle tip-in event, including calculating a speed difference between engine speed and turbine speed, and reducing a pressure command to a designated clutch of the transmission to a threshold level. The method also include setting an upper limit on engine torque, flaring the turbine speed during the tip-in event, and using proportional-integral-derivative control logic of a controller to reduce flare to about zero in a calibrated duration, thereby allowing the clutch to dissipate engine inertia and minimize the severity of the tip-in bump. A transmission in a vehicle is operatively connected to an engine and has a torque converter with a turbine. The transmission includes a clutch and a controller configured to manage tip-in bump performance in the transmission via the above method.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a method and a system for controlling tip-in bump performance in a transmission. 
     BACKGROUND 
     An automatic transmission includes gear elements and clutches that selectively couple input and output shafts of the transmission to establish a desired output speed ratio. Clutch engagement is typically achieved via a controlled application of fluid pressure. The applied fluid pressure moves a clutch piston into engagement with a clutch pack. Shifting from one speed ratio to another is performed automatically by a transmission controller. At throttle tip-in, i.e., the period after a driver requests additional engine torque when engine speed is less than turbine speed but before the requested torque is delivered to the drive train, a perceptible pressure spike or bump may occur in transmission output torque as the engine momentarily freewheels. The difference in engine and turbine speed in a hydrodynamic torque converter at tip-in is proportional to the severity of the experienced bump. Bump severity can also vary with the particular design of the vehicle engine mounts which otherwise may help absorb or dampen some of the inertia of the engine. 
     SUMMARY 
     A method and system are disclosed herein for controlling tip-in bump performance in a transmission. Conventional approaches such as actively profiling engine torque delivered to the transmission may be replaced with the present approach, which instead uses available clutch information and proportional-integral-derivative (PID) control logic to control the tip-in bump via a clutch. Output torque is directly associated with clutch torque. Therefore, the clutch torque of a designated clutch engaged in the driveline can be decreased before throttle tip-in to absorb the force of the bump. This will cause a temporary flare to occur in turbine speed as the clutch slips, with the severity of the flare varying with the severity of the bump. The PID control logic can be used to recover the flare to about zero in a controlled manner with minimal perceptibility to a driver or passenger of the vehicle. The controlled clutch is thus effectively slipped in a closely controlled manner to dissipate clutch inertia as heat. 
     In particular, a method of managing tip-in bump in an automatic transmission includes detecting a set of conditions indicative of an impending tip-in event, including calculating a speed difference between engine speed and turbine speed. The method also includes reducing a pressure command to a designated clutch of the transmission to a threshold level, e.g., a critical holding capacity, when these conditions are present. 
     Additionally, the method includes setting an upper limit on engine torque, flaring the turbine speed during the tip-in event by allowing the clutch to slip, and using proportional-integral-derivative (PID) control logic of a controller to reduce the flare within a calibrated duration, thereby allowing the clutch to dissipate engine inertia as heat and thereby minimize the perceived severity of the tip-in bump to a driver or passenger. This may entail ramping engine torque at a first rate and clutch torque at a second rate that is less than the first rate until the flare is lowered to a calibrated range of zero. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a vehicle having an automatic transmission and a controller which executes the present method controlling tip-in bump in the transmission. 
         FIG. 2  is an example lever diagram for a transmission having clutches that may be designated as control clutches for execution of the present method. 
         FIG. 3  is an example lever diagram for another transmission whose clutches may be designated as control clutches for execution of the present method. 
         FIG. 4  is a flow chart describing an example embodiment of the present method. 
         FIG. 5  is a set of traces describing various clutch control values used during execution of the present method. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, and beginning with  FIG. 1 , a vehicle  10  includes a controller  26 , e.g., a transmission control unit, which selectively executes the present method  100 . An example of method  100  is shown in  FIG. 4  and described in detail below in conjunction with  FIG. 5 . Execution of the present method  100  by the controller  26  enables the controller  26  to control tip-in bump performance as noted above. Example clutches that may be designated as control clutches for execution of the present method  100  are described in detail below with reference to  FIGS. 2 and 3 . 
     The vehicle  10  of  FIG. 1  includes an internal combustion engine  12 . The engine  12  is coupled to an automatic transmission  14  via a hydrodynamic torque converter  16 . The engine  12  delivers engine torque (arrow T E ) via an engine shaft  13  which rotates at engine speed (arrow N E ). The transmission  14  includes a transmission input shaft  15  which rotates at an input speed (arrow N T ). Transfer of input torque (arrow T I ) to the transmission  14  occurs through the torque converter  16 , as is well understood in the art and as described below. At throttle tip-in, the difference in engine speed (arrow N E ) and turbine speed (arrow N T ) may result in a perceptible disturbance referred to as tip-in bump. The controller  26  therefore is configured as set forth herein to minimize the severity of the tip-in bump via clutch control according to the present method  100 . 
     The transmission  14  of  FIG. 1  also includes an output shaft  18 . The output shaft  18  ultimately conveys transmission output torque (arrow T O ), which is transmitted via various clutch and gear sets  17  of the transmission  14 , to a set of drive wheels  24 . The clutch and gear sets  17  can be selectively actuated by electro-hydraulic controls (not shown) powered by fluid delivered under pressure from a fluid pump  33 . The pump  33  draws fluid  37  from a sump  35 . 
     The example transmission  14  of  FIG. 1  may be configured as any multi-speed transmission. The two example transmissions provided herein for illustrative purposes are an 8-speed transmission  14  ( FIG. 2 ) and a 6-speed transmission  114  ( FIG. 3 ). During throttle tip-in, the particular rotating and/or braking clutches of the transmissions  14  and  114  described herein used to control tip-in bump will vary depending on speed ratio. The clutch could be any engaged clutch anywhere along the driveline. 
     The controller  26  may be be configured as a microprocessor-based device having such common elements as a microprocessor or CPU, and/or read only memory (ROM), random access memory (RAM), electrically-programmable read-only memory (EPROM), etc., some of which may be designated as the memory  95  noted above. The controller  26  also includes logic circuitry including but not limited to proportional-integral-derivative (PID) control logic  90 , a high-speed clock (not shown), analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, a digital signal processor or DSP, and the necessary input/output (I/O) devices and other signal conditioning and/or buffer circuitry. 
     The controller  26  uses proportional-integral-derivative (PID) control logic  90  to execute the present method  100 . As is well understood in the art, PID control uses three feedback terms: a proportion (P) term, an integral (I) term, and a derivative (D) term. Each term represents the respective present, past, and future error values. The control logic responsible for generating the I term is generally referred to as an integrator. A controller using PID control logic, e.g., the present controller  26 , calculates an error value in a given process variable as a difference between a measured value and a desired/calibrated value and thereafter controls process inputs as a function of the three control terms. 
     Still referring to  FIG. 1 , an engine control unit (ECU)  29  may be used either as a separate device as shown or integrated with the controller  26 . If separate, the controller  26  may be in communication with the ECU  29  as indicated by double-headed arrow  21 . The controller  26  may request a specific level of managed engine torque (arrow  11 ) from the ECU  29  as needed, and may receive any engine control values the controller  26  might require in the execution of method  100 , e.g., engine speed, engine torque, and/or any other modeled engine control values. 
     The torque converter  16  shown in  FIG. 1  has a stator  30  positioned between a pump  32  and a turbine  34 . A torque converter clutch  31  may also be used to selectively lock the pump  32  to the turbine  34  above a threshold lockup speed, as will be understood by those of ordinary skill in the art. The pump  32  may be coupled to the output shaft  13  to thereby rotate at engine speed (arrow N E ). Within the torque converter  16 , the turbine  34  is driven by fluid  37 , with the turbine  34  in turn connected to the input shaft  15  of the transmission  14 . Thus, rotation of the turbine  34  ultimately rotates the input shaft  15  at a turbine speed, which is the same as the input speed (arrow N T ) noted above. Turbine speed (arrow N T ) will ordinarily be than or equal to engine speed (arrow N E ), with viscous drag or friction losses within the transmission  14  tending to reduce the turbine speed (arrow N T ) to a level somewhat less than engine speed (arrow N E ), as will be readily understood by those of ordinary skill in the art. At certain times, however, the engine  12  will coast, and thus the engine speed (arrow N E ) will drop below turbine speed (arrow N T ). Throttle tip-in at this time can result in the tip-in bump noted above. 
       FIGS. 2 and 3  illustrate two possible transmissions  14  and  114 , respectively that may be controlled to minimize the severity of any tip-in bump using the present method  100 . The transmission  14  of  FIG. 2  is an example 8-speed transmission having four planetary gear sets  40 ,  50 ,  60 , and  70 . The transmission  114  of  FIG. 3  is an example 6-speed transmission having two planetary gear sets  140  and  150 . Other transmission configurations may be readily envisioned that could be controlled in the manner described below to control tip-in bump, and therefore the transmissions  14  and  114  are not limiting. 
     Referring to  FIG. 2 , the example transmission  14  may include a braking clutch CB 1278 R, i.e., clutch  36 . The nomenclature CB 1278 R represents that this particular device is a braking clutch (CB), and is engaged in each of 1 st , 2 nd , 7 th , 8 th , and reverse (R) gears. The transmission  14  also includes another braking clutch CB 12345 R, or clutch  41 , which selectively connects an element of a first gear set  40  to a stationary member  28  when engaged. Clutches  36  and  41  are connected to respective nodes  42  and  46  of first gear set  40 . In one embodiment, node  42  can be a sun gear (S 4 ) of the gear set  40 , while node  46  may be a ring gear (R 4 ) of the same gear set. Gear set  40  also includes a node  44 , which may be a carrier member (PC 4 ) in the embodiment shown. 
     Node  42  is also connected to a node  52  of a second gear set  50 . Node  54  of gear set  50  is connected to an input side of a rotating clutch C 13567 , i.e., clutch  38 , as is the transmission input shaft  15  with input torque (arrow T I ). Node  56  is connected to a third gear set  60  as explained below. In one embodiment, gear set  50  may be a planetary gear set wherein nodes  52 ,  54 , and  56  are a sun gear (S 1 ), a carrier member (PC 1 ), and a ring gear (R 1 ), respectively. 
     The third gear set  60  includes nodes  62 ,  64 , and  66 , which in one embodiment may be ring gear (R 2 ), carrier member (PC 2 ), and sun gear (S 2 ), respectively. A rotating clutch C 23468 , i.e., clutch  58 , may be connected between the output of clutch  38  and node  66 , and between node  56  of gear set  50  and node  66  of gear set  60 . Node  62  may be connected to a fourth gear set  70  having nodes  72 ,  74 , and  76 . Nodes  72 ,  74 , and  76  may be a sun gear (S 3 ), carrier member (PC 3 ) and ring gear (R 3 ), respectively. In particular, node  62  may be connected to node  72  via a rotating clutch C 45678 R, i.e., clutch  48 . Node  64  of gear set  60  may be directly connected to node  74  of gear set  70 , which in turn may be connected to the transmission output shaft  18  (also see  FIG. 1 ). Nodes  44  and  76  may be continuously connected via an interconnecting member  45 . Nodes  64  and  74  may be continuously connected via an interconnecting member  47 . The particular clutch controlled during throttle tip-in according to the present method  100  of  FIG. 4  in the 8-speed transmission  14  will vary with the start and end states or speed ratios as noted above. However, in general if the clutch is engaged during a particular gear, that clutch may be controlled as set forth hereinbelow. 
     Referring to  FIG. 3 , the transmission  14  of  FIG. 1  may be embodied as a 6-speed transmission  114 . In this embodiment, the transmission input shaft  15  may be connected to a first gear set  140  having nodes  142 ,  144 , and  146 , which may be embodied as a ring gear (R 3 ), carrier member (PC 3 ), and sun gear (S 3 ) as shown. The input shaft  15  may be directly connected to node  142 , and to a clutch C 456 , i.e., clutch  51 . Node  144  is connected to a clutch C 1234 , i.e., the clutch  138 , and to an input side of a rotating clutch C 35 R, i.e., clutch  53 . Node  146  is grounded to the stationary member  28 . 
     A second gear set  150  includes nodes  152 ,  154 ,  156 , and  158 , which may be embodied as a sun gear (S 1 ), ring gear (R 1 ), carrier gear (PC 1 ), and another sun gear (S 2 ), respectively. Node  158  may be connected to the stationary member  28  via a braking clutch CB 26 , i.e., clutch  43 . Node  154  is directly connected to the transmission output shaft  18 . Node  156  is connected to a braking clutch CBR 1 , i.e., clutch  136 , which is also connected to a stationary member  28 . As with the 8-speed transmission  14  of  FIG. 2 , the particular clutch of the 6-speed transmission  114  controlled by the controller  26  in execution of the present method  100  will vary with the start and end states/speed ratios as noted above. 
     Referring to  FIG. 4  in conjunction with the shift control time traces  80   FIG. 5 , an example embodiment of the present method  100  commences at step  102 . In  FIG. 5 , time is plotted on the horizontal axis and amplitude is plotted on the vertical axis. In step  102 , the controller  26  of  FIG. 1  determines whether a throttle tip-in event may be imminent. This step may entail measuring engine speed (N E ), i.e., trace  82  of  FIG. 5 , and turbine speed (N T ), i.e., trace  83 , comparing the two measured values, and then determining when and to what extent engine speed lags turbine speed and the rate at which the decreasing engine speed (trace  82 ) is approaching turbine speed (trace  83 ). Step  102  is repeated until conditions are present that are indicative of conditions prior to throttle tip-in. 
     At step  104 , at about point  79  which occurs at about t 1 , the decreasing engine speed (trace  82 ) crosses turbine speed (trace  83 ). Clutch torque (trace  93 ) is reduced according to a calibrated profile, which is represented in  FIG. 5  as trace  87 . That is, the controller  26  of  FIG. 1  reduces the clutch torque (trace  93  of  FIG. 5 ) of a designated clutch to a calibrated pressure, for instance at or just above critical holding pressure for that clutch. This value may be determined from a previously-learned clutch torque/pressure relationship for that clutch, and thus is a calibrated value. Trace  93  is also labeled T C  in  FIG. 5 , i.e., “clutch torque”, for added clarity. 
     At step  106 , the controller  26  of  FIG. 1  may activate PID logic  90  so that the PID logic  90  is ready to manage any flare in turbine speed (trace  83 ) that might result from the present control action, as set forth below. At this point, which occurs at about t 2  in  FIG. 5 , the engine  12  of  FIG. 1  is coasting or imparting negative torque. 
     At step  108 , the controller  26  may set/record an upper torque threshold for the engine torque (trace  81 ) based on the difference in speed, i.e., (N T −N E ). For instance, if the difference is 200 RPM, 40 Nm of torque may be required if engine inertia is about 0.03 Nm/s/s, which may allow the engine speed to cross the turbine speed, i.e., point  89 , in about 150 msec. Engine torque may drop to the level of trace  88 , which may be zero in one embodiment, before t 1  until shortly before t 3  as shown. 
     At step  110 , the controller  26  of  FIG. 1  may begin to slip the designated clutch. Just before t 3 , as engine speed (trace  82 ) begins to ramp up, engine torque (trace  81 ) steps up and is held until t 4 . Turbine speed (trace  83 ) will begin to flare at or just after about t 3 , as indicated by trace  86 . As output torque from the transmission  14  is directly associated with clutch torque, step  110  effectively includes dissipating engine inertia during throttle tip-in as heat to thereby lessen the severity of the tip-in bump. Such a bump may be detected by a transmission output speed sensor (TOSS), with the signal from such a TOSS represented in  FIG. 5  as trace  84 , and with the bump and subsequent decay thereof indicated by arrow  85 . The amount of slip to be introduced by the controller  26  can vary, for instance proportionally to the speed difference between engine speed (N E ) and turbine speed (N T ). 
     At step  112 , the controller  26  of  FIG. 1  uses the active PID control logic  90  of  FIG. 1  after t 4  to manage the turbine flare (trace  86 ), and to smoothly reduce the flare (trace  86 ) to within a calibrated range of zero, e.g., ±5 RPM, without an additional inertia bump. This may occur by ramping the engine torque (trace  81 ) after t 4  at a lesser rate than the ramp rate of the clutch torque (trace  93 ) after the same point over a calibrated period, e.g., about 200-400 msec. 
     At step  114 , the controller  26  determines whether flare (trace  86 ) is back under control, which is defined herein as being within the calibrated range noted above with respect to step  112 . If so, the method  100  returns to step  102  and begins anew. If flare (trace  86 ) is still not under control, step  112  may be repeated until the PID control logic  90  has reduced flare (trace  86 ) to the target level. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.