# Patent

## Title
Vehicle response during vehicle acceleration conditions

## Abstract

A vehicle control method for a vehicle having powertrain with an internal combustion engine and a transmission having a clutch, the method comprising of transitioning through a lash region of the transmission during clutch slipping conditions in response to a driver tip-in; and during the transition, first retarding ignition timing past maximum torque timing while increasing engine airflow, and then second, advancing ignition timing from the retarded timing while continuing to increase engine airflow.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present application is a divisional of U.S. patent application Ser. No. 11/423,684, filed Jun. 12, 2006, entitled “Improved Vehicle Response During Vehicle Acceleration Conditions”, which is a continuation-in-part of U.S. patent application Ser. No. 11/370,400, filed Mar. 7, 2006, entitled “System and Method for Improved Vehicle Response During Vehicle Acceleration Conditions”, the entire contents of each of which are incorporated herein by reference.


FIELD
The present application relates to engine and vehicle control, and in one example relates to operation during vehicle acceleration following deceleration.
BACKGROUND AND SUMMARY
Internal combustion engines are controlled in many different ways to provide acceptable driving comfort during all operating conditions. Some methods use engine output, or torque, control where the actual engine torque is controlled to a desired engine torque through an output adjusting device, such as with an electronic throttle, ignition timing, or various other devices.
Under some conditions, there is the potential for poor driveability when the vehicle operator releases and subsequently engages the accelerator pedal. Specifically, as described in U.S. Pat. No. 6,266,597, transmission or driveline gear lash crossing during such conditions can degrade driver feel. For example, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission or driveline separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, which if transmitted to the driver is called clunk, resulting in poor driveability and customer dissatisfaction.
This disadvantage of the prior art is exacerbated when the operator returns the accelerator pedal to a depressed position, indicating a desire for increased engine torque. In this situation, the zero torque transition point must again be traversed. However, in this situation, the engine is producing a larger amount of torque than during deceleration because the driver is requesting acceleration. Thus, another, more severe, impact is generally experienced due to the transmission or driveline lash during the zero torque transition.
As such, in U.S. Pat. No. 6,910,990, the system controls engine torque to transition through the transmission or driveline lash zone by limiting a rate of torque increase during such conditions. In other words, when near the transmission lash zone, engine torque is adjusted at a predetermined rate until the system passes through the transmission lash zone. Further, the limiting may be adjustable based on operating conditions. By varying the limitation on the torque change in this way, driveability can be improved.
However, the inventors herein have recognized a disadvantage with such an approach. In particular, while rate limiting torque changes may reduce clunk, it may also increase a response delay to the point noticeable by the driver. Further, the greater the reduction in clunk (i.e., the more torque increases or decreases are limited), the greater the response delay.
In this way, it may be possible to coordinate multiple torque actuators during a driver tip-in to both reduce clunk without substantially increasing total response time, while also providing improved operation for both slipping and non-slipping conditions. For example, by coordinating throttle and ignition timing adjustments during a driver tip-in in this way, it is possible to, in effect, increase pre-charging of the intake manifold and cylinders with airflow so that once the transition through the lash zone is complete, a more rapid torque increase is possible. As another example, by adjusting operating depending on whether slipping or non-slipping transmission conditions are present, it is possible to manage the lash transition for a fully locked transmission driveline.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a vehicle illustrating various powertrain components;
FIG. 2 is a block diagram of an engine;
FIG. 3 is a high level flowchart of a routine for controlling the engine and powertrain;
FIG. 4 is a graph illustrating example operation;
FIG. 5 is a state diagram of example control logic and routines;
FIG. 6 is a timing diagram showing example operation according to FIG. 5;
FIG. 7 is a graph illustrating additional example operation; and
FIGS. 8-11 are high level flowcharts of routines for controlling the engine and powertrain.



DETAILED DESCRIPTION
Referring to FIG. 1, internal combustion engine 10, further described herein with particular reference to FIG. 2, is shown coupled to torque converter 11 via crankshaft 13. Torque converter 11 is also coupled to transmission 15 via turbine shaft 17. Torque converter 11 has a bypass clutch (not shown) which can be engaged, disengaged, or partially engaged. When the clutch is either disengaged or being disengaged, the torque converter is said to be in an unlocked state. Turbine shaft 17 is also known as transmission input shaft.
In one embodiment, transmission 15 comprises an electronically controlled transmission with a plurality of selectable discrete gear ratios. Transmission 15 may also comprises various other gears, such as, for example, a final drive ratio (not shown). Alternatively, transmission 15 may be a continuously variable transmission (CVT). In still another example, transmission 15 may be a manual transmission, an automated manual transmission, a powershift transmission, an automatic transmission with locked or controlled slip of the converter clutch, or various others.
Transmission 15 may further be coupled to tire 19 via axle 21. Tire 19 interfaces the vehicle (not shown) to the road 23. Note that in one example embodiment, this powertrain is coupled in a passenger vehicle that travels on the road.
Note that various of the above components may be eliminated, such as the torque converter, for example.
Internal combustion engine 10 comprising a plurality of cylinders, one cylinder of which is shown in FIG. 2, is controlled by electronic engine controller 12. Engine 10 includes combustion chamber 30 and cylinder walls 32 with piston 36 positioned therein and connected to crankshaft 13. Combustion chamber 30 communicates with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Exhaust gas oxygen sensor 16 is coupled to exhaust manifold 48 of engine 10 upstream of catalytic converter 20.
Intake manifold 44 communicates with throttle body 64 via throttle plate 66. Throttle plate 66 is controlled by electric motor 67, which receives a signal from ETC driver 69. ETC driver 69 receives control signal (DC) from controller 12. Intake manifold 44 is also shown having fuel injector 68 coupled thereto for delivering fuel in proportion to the pulse width of signal (fpw) from controller 12. Fuel is delivered to fuel injector 68 by a conventional fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown).
Engine 10 further includes conventional distributorless ignition system 88 to provide ignition spark to combustion chamber 30 via spark plug 92 in response to controller 12. In the embodiment described herein, controller 12 is a conventional microcomputer including: microprocessor unit 102, input/output ports 104, electronic memory chip 106, which is an electronically programmable memory in this particular example, random access memory 108, and a conventional data bus.
Controller 12 receives various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: measurements of inducted mass air flow (MAF) from mass air flow sensor 110 coupled to throttle body 64; engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling jacket 114; a measurement of throttle position (TP) from throttle position sensor 117 coupled to throttle plate 66; a measurement of turbine speed (Wt) from turbine speed sensor 119, where turbine speed measures the speed of shaft 17, and a profile ignition pickup signal (PIP) from Hall effect sensor 118 coupled to crankshaft 13 indicating an engine speed (N). Alternatively, turbine speed may be determined from vehicle speed and gear ratio.
Continuing with FIG. 2, accelerator pedal 130 is shown communicating with the driver's foot 132. Accelerator pedal position (PP) is measured by pedal position sensor 134 and sent to controller 12.
In an alternative embodiment, where an electronically controlled throttle is not used, an air bypass valve (not shown) can be installed to allow a controlled amount of air to bypass throttle plate 62. In this alternative embodiment, the air bypass valve (not shown) receives a control signal (not shown) from controller 12.
As described above, the present application is directed, in one example, to solving disadvantages that occur when the driver “tips-in” (applies the accelerator pedal) after the torque in the driveline has transitioned into the negative region. In such cases, the driveline elements will have to transition through their lash region to provide positive torque to the wheels, where the transition through the lash region can produce an objectionable “clunk” if the impact velocity of the driveline elements is too fast.
In an automatic transmission vehicle, to have positive torque produced by the torque converter and transmitted to the driveline, the engine speed must be above turbine speed and the turbine speed must be at the synchronous turbine speed or the converter bypass clutch must have some capacity to transmit torque and the engine torque is positive and the slip across the clutch is non-negative. (The torque converter slip (engine speed-turbine speed) is greater than 0 when positive torque is being delivered). If the transition from negative to positive converter slip and/or torque is not properly managed, then the engine can accelerate too fast through this region (beginning to produce positive torque) or the converter clutch torque can rise too fast resulting in a higher rise rate of output shaft torque accelerating the elements in the driveline. Higher torque levels before the lash in the driveline being taken up can then produce higher impact velocities and make “clunk” more likely. To a first approximation for an “open” converter, the rise rate of torque in the driveline (non-shifting) may be proportional to the rate of engine acceleration when the engine speed>synchronous turbine speed.
Under some conditions, the engine should be controlled so that the engine torque and/or acceleration is reduced sufficiently while the driveline elements are accelerating to produce positive driveline torque, but the engine torque/acceleration and driveline torque should also be responsive to the driver's demand before and after this transition so that the driver perception of any lag in the engine response is reduced.
While an engine torque estimation model in the controller can be used, errors in the estimation can reduce estimate accuracy and thus the precision to indicate whether the driveline torque is slightly positive or slightly negative. As such, in one embodiment that can be used alone or in addition to a torque estimate, additional measurements, such as torque converter input and output speeds can be used to accurately indicate when the vehicle is beginning and ending transitioning through the lash region, even in the presence of external noise factors.
Specifically, in one example for a torque converter equipped vehicle, a tip-in management and control routine can be used to adjust engine torque control to control engine acceleration just as the engine speed is exceeding turbine speed. Further, the engine torque may be controlled via multiple actuators, such as using slower throttle control and faster ignition timing control in a coordinated way to minimize any driver perception of rate limited torque during the transition through the lash region. For example, various example engine control strategies using coordinated throttle and spark control to manage the transition from negative driveline torque to positive driveline torque through driveline lash with improved robustness and responsiveness is described below with regard to FIGS. 3-7. Because of the coordinated use of throttle and spark and the triggering of control system actions based on measured speeds across a torque converter, the operation of this system can provide various advantages as noted herein.
Referring now to FIG. 3, a routine is described for controlling engine and vehicle operation during a driver tip-in where the transition through a gear lash zone for an open converter configuration is managed while still providing acceptable increasing torque response. In 310, the routine determines whether a previous driver tip-out has been detected and the torque converter is unlocked, or partially un-locked. In one example, the routine determines whether the driver is depressing the accelerator pedal by determining whether the pedal position is less than the preselected value. Note that this preselected value can be an adaptive parameter that tracks variations in the closed pedal position due to sensor aging, mechanical wear, and various other factors. Also note that in response to a driver tip-out being detected, powertrain output may be decreased so that positive torque is not transmitted to the wheels, for example, the wheels may be driving the engine through the transmission and/or torque converter. Further, during some tip-out conditions, fuel injectors may be deactivated to further reduce engine torque (or increase engine braking), possibly improving fuel economy. However, may be considered in some examples when transitioning through the lash zone, for example.
When the answer to 310 is YES, the routine continues to 312. In 312, the routine determines whether a substantial driver tip-in has been detected. Again, this may be determined based on pedal position, or the corresponding increase in desired torque caused by depression of the driver pedal, for example. If so, the routine continues to 314.
In 314, the routine decides whether the powertrain is in or near a gear lash zone. For example, the routine may utilize the torque converter input and output speeds to determine whether the speeds are within a selected range of equal speeds, for example, and whether the speeds are greater than a synchronous speed, for example. If not, the routine continues to 318 where a requested torque increase may be provided by a throttle increase and an advance of ignition timing (if the current timing is retarded from a maximum torque timing, for example).
Otherwise, if the answer is YES to 314, the routine continues to 316 to determine whether torque increase rate limiting is selected based on operating conditions. For example, the routine may determine whether to limit a rate of torque increase during the lash zone to reduce a potential impact caused by such lash as noted herein. If so, the routine continues to 320 to limit torque increase by retarding ignition timing while still increasing airflow by increasing the throttle angle, for example. In this way, it is possible to limit torque increase during transitions through the lash zone via spark retard, yet by continuing an increase in airflow without the limitation such as in prior approaches, the torque can be even more rapidly increased once through the lash zone. Such operation is illustrated in more detail in the prophetic example of FIG. 4.
Specifically, FIG. 4 shows an example response to a driver tip-in where the powertrain output torque transitions from negative to positive, as shown by the top graph. The lash zone, or approximately zero torque transmission location is illustrated with the dashed horizontal line, where the lower dotted line indicates an example speed ratio threshold (e.g., torque converter input speed is 0.95 of torque converter output speed) and the upper dotted line indicates an example speed ratio threshold (e.g., torque converter input speed is 1.05 of torque converter output speed). Below the powertrain output torque the graph illustrates driver pedal position (APP) and then throttle position (TP) of an electronically controlled throttle plate. Below throttle position the graph illustrates ignition timing, and specifically timing relative to a maximum torque timing (mbt), where spark timing below the mbt line represents retard from mbt. Finally, the bottom illustration shows the airflow response.
FIG. 4 shows three example response, with the first (A) illustrating a tip-in with no mitigation in ignition timing or airflow, and thus the most likely to cause objectionable clunk; the second (B) illustrating a tip-in with a limitation of engine torque via the throttle, or airflow, which may be used to reduce the effect of clunk; and the third (C) illustrating compensation via coordination of throttle and spark in accordance with FIG. 3.
In the first response (A), neither engine torque, nor throttle, nor spark, are used to rate-limit the powertrain output during the transition through the lash zone. Thus, clunk may be experienced under some conditions; however a quick response is experienced by the driver.
In the second response (B), throttle position is used to rate limit torque increase during the transition. Once through the lash zone, the throttle can then continue to increase unrestricted to deliver the driver requested torque. However, while the limiting may reduce clunk, driver response may be reduced by the delay in delivering airflow, due to the combination of manifold dynamics, throttle dynamics, and the rate limiting. In other words, as shown by FIG. 4, the torque response in B is permanently delayed from A.
In the third response (C), coordination of throttle position and spark retard are used to transition through the lash zone, while still providing acceptable response. As shown by FIG. 4, while there is a period of delay in response when transitioning through the lash zone, the torque response of C is able to “catch up” to the torque response of A. By using spark retard during the transition, while allowing airflow to continue to rise substantially un-restricted, it is possible to both reduce clunk, and maintain driver performance over a longer scale.
Returning to 320, the level to which engine torque can be managed or reduced relative to requested output may be dependent on operating conditions, in one embodiment. For example, an allowable rate of increase in engine torque may be based on various factors, such as based on information that relates to status and conditions of the engine and vehicle indicative of whether and to what extent clunk can affect drive feel, and the extent rate limiting requested engine torque may reduce vehicle response. In particular, in one example, the routine utilizes the sensed accelerator pedal position (PP), the torque converter speed ratio, the vehicle speed, and the ratio of vehicle speed to engine speed. In one example, the allowable rate of increase may be determined as a four dimensional function of the pedal position, speed ratio, vehicle speed, and engine speed to vehicle speed ratio.
Concluding the discussion of FIG. 3, if the answer to 314 or 316 is no, the routine continues to 318 in this example.
Referring now to FIG. 5, an alternative embodiment illustrated via a state diagram is shown. Specifically, each block shows a control logic state, with transitions amount the states shown by lines, where the direction of the transition is indicated with an arrow. Further the blocks indicate their state value (e.g., block 510 is STATE 0, as indicated by the mode parameter tq_tim_mode). Further, each block indicates potential states to which the control may transition via the numbers in parenthesis.
Block 510 shows STATE 0, in which control logic for making engine adjustments for transitioning through the lash zone in response to a tip-in are not activated. Specifically, the logic is disarmed, and the system is at part pedal (e.g., the driver is partly tipped in) waiting for a tip-out. Further, there is currently no adjustment to engine throttle angle or ignition timing (SAI). As indicated in the parenthesis, from block 510, the control may transition to either STATE 1, or stay in STATE 0.
512 shows a transition from STATE 0 to STATE 1, which may be based on several alternative conditions. A first transition condition is based on torque converter slip, in either an overrunning or non-overrunning condition. Specifically, if negative slip and a low torque request (i.e., less than a threshold value TQ_ARM) are detected, the state transitions. A second transition condition is independent of slip, but rather based on a low actual torque (i.e., less than a threshold value TQ_ARM) being detected. Additional parameters may also be considered in this transition, including whether the gear command is greater than a minimum gear or the turbine speed (calculated via a turbine speed sensor or an estimated turbine speed from gear ratio and vehicle speed), and whether a transmission shift is in progress and a flag has been set to disable the torque management through the transition when a shift is in progress. In one example, when a shift is in progress, the transition is not enabled. In one particular example, in response to a non-slip condition and when the transmission is in gear and the estimated engine torque is below a threshold (TQ_ARM), the transition may be performed because driveline torque is determined to be negative.
Note that a non-slip condition may refer to conditions where a torque converter is locked, or only partially transmits torque through a partially locked condition. Further, it may refer to a manual transmission in a fixed gear, for example. In still another example, a non-slip condition may be detected as illustrated in FIG. 8.
514 shows a transition from STATE 1 to STATE 0, which may occur based on slip for either an overrunning or non-overrunning condition in which the routine identifies whether the powertrain has reached a positive slip value (e.g., torque converter input speed greater than torque converter output speed, or whether the transmission is in neutral or disabled. Alternatively, the transition may occur independent of slip based on whether the powertrain has reached a positive actual torque (i.e., greater than a threshold value TQ_DISARM). Again, additional parameters may also be considered in this transition, including whether the gear command is less than a minimum gear or the turbine speed (calculated via a turbine speed sensor or an estimated turbine speed from gear ratio and vehicle speed) with hysteresis, and whether a transmission shift is in progress and a flag has been set to disable the torque management through the transition when a shift is in progress. In one example, when a shift is in progress, the transition is enabled. In one particular example, in response to a non-slip condition and when the transmission is in gear and the estimated engine torque is above a threshold (TQ_DISARM), the transition to STATE 0 occurs because driveline torque is determined to no longer be negative.
Block 516 shows STATE 1, in which control logic prepares for a tip-in. In this case, the control logic for making adjustments during a transition to a driver tip-in through the lash zone is armed, and the routine is waiting for a tip-in to occur. Further, there is currently no additional lash-based adjustment to engine throttle angle or ignition timing (SAI) in this state. As indicated in the parenthesis, from block 516, the control may transition to either STATES 3, 2, or 0. While in STATE 1, the vehicle powertrain torque levels at the driver axle are low or negative, depending on operating conditions.
518 shows a transition from STATE 1 to STATE 2 based on whether a significant positive torque request (i.e., desired torque increases past a threshold level) is detected. Further, 520 shows a transition from STATE 2 to STATE 1 based on whether a torque request has dropped (i.e., below a lower threshold) and is below a torque control level. In one embodiment, the threshold for driver demand torque to transition to STATE 2 may be based on the current estimate of engine brake torque if a non-slip condition is detected. 522 shows a transition from STATE 1 to STATE 3 which may be based on slip in either an overrunning or non-overrunning condition, such as based on whether the torque converter speed ratios have entered a range of lash values, such as between 0.95 and 1.05. In this case, the system can be determined to have begun a transition through lash region based on slip. Alternatively, the transition may be independent of slip, such as based on whether actual torque becomes greater than a threshold. In one embodiment, during a non-slip condition and when the driver pedal is applied or speed control is active, when driver demanded torque is increasing sufficiently past a threshold, and when the estimated engine torque is above a threshold (TQ_TRG), the transition from STATE 1 to STATE 3 is performed because engine torque is indicating a tip-in may be in progress that is about to cross lash.
Block 524 shows STATE 2, in which control logic increases engine torque. In this case, the control logic detects a positive torque request that may produce clunk, and calculates a limited airflow increase as the lash region is approached. Specifically, a throttle position of the electronically controlled throttle is clipped. Also in STATE 2, the airflow, or throttle torque, limit may be unconditionally ramped up from the initial value where the ramp is conditional based on engine acceleration for a slipping driveline, when such a slip is present. As indicated in the parenthesis, from block 524, the control may transition to either STATES 4, 3, 1, or 0.
526 shows a transition from STATE 2 to STATE 3 which may be non-slip based via a exceeding a timer. Alternatively, the transition may be slip based in either an overrunning or non-overrunning condition based on whether the powertrain has begun to transition through lash region based on torque converter speeds, e.g., has the ratio of torque converter input speed to torque converter output speed risen above a threshold value (e.g., 0.95). Still further, the transition can be non-slip based, such as whether the powertrain has begun to transition through the lash region based on actual engine torque. In one embodiment, during non-slip conditions and when the system has been in STATE 2 for greater than a calibratible amount of time, the transition to STATE 3 is performed to reduce driver perceived hesitation. In another embodiment, during non-slip conditions and when the estimated engine torque is above a threshold (TQ_TRG), the routine transitions to STATE 3 because engine torque indicates the driveline is about to cross lash.
528 shows a transition from STATE 2 to STATE 4 which may be based on torque converter slip values and a timer value (e.g., exceeding a threshold time in STATE 2). Further, 530 shows a transition from STATE 2 to STATE 0 which also may be based on torque converter slip values and a timer value (e.g., exceeding a threshold time in STATE 2).
Block 532 shows STATE 3, in which control logic holds or rate-limits engine and/or powertrain torque. In this case, the control logic adjusts spark timing (e.g., ignition timing retard from maximum torque timing) and optionally throttle position to clip engine torque and/or acceleration using a torque rate limit to reduce clunk through the lash zone. In one embodiment, the initial spark level in this state may be determined as a function of gear or gear ratio during non-slipping conditions.
As indicated in the parenthesis, from block 532, the control may transition to either STATES 4, or 0. For a torque converter where the converter clutch capacity is small enough to allow enough slip such that engine acceleration is clearly related to engine torque and converter hydraulic torque as the dominant dynamics (instead of converter clutch torque), this clipping, holding or rate-limiting of can be conditional based on engine acceleration or slip feedback.
The limitation of electronic throttle position in STATE 2 and spark timing in STATE 3 may be performed differently depending on whether slip-based or non-slip based conditions are present. For example, non-slip based conditions may be present when a torque converter is at least partially locked, when a manual transmission is present, etc. Further, during such non-slip conditions, the spark torque limit and throttle torque limit may be unconditionally ramped up as a function of a desired ramp time, a final spark advance ramp target (TQE_SAI_HLD) and commanded gear and the level of driver demand, where the ramping may be conditional on engine acceleration for a slipping driveline.
534 shows a transition from STATE 3 to STATE 4, which may be based on slip in either an overrunning or non-overrunning condition, such as based on whether the torque converter speed ratios have exited a range of lash values, such as between 0.95 and 1.05 (i.e., whether the powertrain has completed a transition through the lash region based on torque converter speeds, e.g., has the ratio of torque converter input speed to torque converter output speed risen above a threshold value, such as 1.05). The transition may also be triggered independent of slip, and the determination of completing the transition may be based on whether actual torque is greater than a threshold value. Still further, the transition may be triggered by whether a downshift of the transmission gears is in progress, or whether a timer value has been exceeded for a threshold time in STATE 3. In one embodiment, during non-slip conditions, the spark torque command in STATE 3 may be unconditionally ramped toward a target value over a desired period of time. When the target torque of this ramp is reached, the system transitions to STATE 4 to ramp out the remainder of the torque as the lash should have been traversed.
536 shows a transition from STATE 3 to STATE 0 based on whether a torque request returned to a lower torque value and the pedal is in a closed position before a transition through the lash zone is completed, or the transmission is in neutral or disabled. Any of these conditions will thus cause the routine to transition to STATE 0.
Block 538 shows STATE 4, in which control logic ramps in torque increases after completing a transition through the lash zone. Specifically, the limits on spark timing and throttle (if any) are ramped out to make the torque output available to provide the desired driver response. This can be done rapidly or more smoothly, depending on operating conditions, for example. As indicated in the parenthesis, from block 538, the control may transition to STATE 0.
540 shows the only transition from STATE 4, specifically, a transition from STATE 4 to STATE 0. The transition of 540 may be triggered when the ramping of throttle and spark timing is completed (e.g., when ignition timing retard has ramped out), or when a timer for being in STATE 4 has exceeded a threshold.
As previously noted above, the transition diagram of FIG. 5 illustrates an example routine that may be used to control operation through the lash zone to both reduce clunk while still providing a rapid driver response. Further, in this example, both slip based and non-slip based conditions may be used to achieve robust operation over a variety of operation conditions, such as either a locked or unlocked torque converter, manual transmissions, etc.
Further, in one or more of the above states (and in one embodiment in all states), the airflow control and/or the spark control can be subject to overrides based on driver input (pedal position, rate, or some combination) so that as the driver demand increases the system responsiveness can also increase. See, for example, the driver override as illustrated in FIG. 9. Further, in one, some, or all states, the torque, airflow and spark limiting can be subject to overrides based on commanded transmission downshifts and downshifts that are ‘in progress’ (ratio is changing) to bring engine torque up quickly to enable the transmission to make a smooth and responsive shift. For example, torque, airflow and spark limiting can be subject to overrides in all states if a downshift commanded based on driver demand is detected. See, for example, the shift override of FIG. 10 which may be performed in STATE 2, and/or the downshift override of FIG. 11 which may be performed in STATE 3. Finally, transitions between modes, or the timing or use of some limiting states are responsive to driver demand downshifts in progress (transmission ratio starting to change), and slip based transitions may be disabled during any non-slipping conditions.
Referring now to FIG. 6, it shows a timing diagram corresponding to the operation of FIG. 5. Specifically, it shows the response to a driver tip-in during various STATES, or modes, and illustrates adjustments to both throttle position and ignition timing. In the graph, the following labels are used: L2 is the initial mode 2 torque command level for throttle and spark, L3 is the initial mode 3 torque command level for spark, R2 is the rate of increase in the throttle and spark torque commands during mode 2, R3a is the rate of increase in the throttle command during mode 3 (note that the throttle command does not step down like the spark command), R3b is the rate of increase for spark in mode 3, and R4a and R4b are similar to R3a and R3b. The graph also illustrates the airflow holding timer (tq_desem_hld_tmr) which counts up during time TM5, and the torque multiplier (tq_desam_mul) which counts down during time TM6. Finally, it shows the enable flag (tq_desem_ena) indicating that the above control logic is active.
Referring now to FIG. 7, another example of system operation is illustrated in which coordinated throttle and spark adjustments are provided to manage driveline lash transition. Specifically, the plot shows the coordinated way that engine airflow is used to accelerate the engine up to turbine speed at maximum spark, then spark is retarded to slow engine acceleration through the driveline lash zone and then torque is again increased rapidly via spark and airflow after lash has been crossed.
The top graph of FIG. 7 shows turbine speed (torque converter output speed) in solid and engine speed (torque converter input speed) in dashed. Further, the bottom graph shows engine airflow in solid and absolute spark advance in dashed. The x-axis of both graphs shows time in seconds. While this example is based on vehicle data, it represents only one example transition, and as noted herein, various alternatives are possible.
During the initial vehicle operation (around 710), the fuel injectors are cut-out (e.g., deactivated). While in this particular example the system incorporates injector cut-out during deceleration or driver tip-out conditions, injector cut-out may also be eliminated. Further, during the initial operation, the torque converter slip (turbine speed−engine speed) is controlled to approximately −50 rpm, e.g., via a lock-up clutch, number of cylinders active, etc. Then, around 712, engine airflow is increased, injectors are activated, and the spark angle is maintained at approximately mbt, in response to a driver tip-in. Then, around 714, a small slip across the torque converter is maintained until the lash zone is crossed via airflow and spark retard control. Around 716, airflow is further increased for good torque response, with spark retarded as needed to hold engine speed through the lash zone and then increase torque quickly. Finally, around 718, the transmission control (e.g., clutch duty cycle) allows the converter to slip as engine torque is increased.
Referring now to FIG. 8, a routine is described for detecting a non-slip condition of the vehicle's powertrain and/or transmission. First, in 810 the routine calculates the absolute value of the difference between the engine speed and a synchronous turbine speed. Next, in 812, the routine determines whether the transmission reports that the torque converter is in an open or at least partially open condition. If the answer to step 812 is no, the routine continues to 814 to determine whether the absolute value of the slip across the torque converter is less than a threshold. If the answer to 812 is yes, or if the answer to 814 is no, the routine continues 816 to clear a non-slip timer. If the answer to 814 is yes, the routine continues 818 to increment the non-slip timer by a Δ time value.
From either 818 or 816 the routine continues to 820 to determine whether or not the non-slip timer is greater than the threshold value or whether the transmission of the vehicle is a manual transmission or other non-slip transmission. If the answer to 820 is no, the routine continues to 822 to indicate a slip condition has been detected. Otherwise, the routine continues to 824 to indicate that a non-slip condition has been detected.
Referring now to FIG. 9, an example driver initiated override for adjusting torque threshold values and transitioning between the STATES of FIG. 5 is shown. The routine of FIG. 9 may be used in one or more of STATES 2, 3, and/or 4. First, in 910, the routine calculates an override torque parameter (OVERRIDE_TORQUE) as a function of various parameters including one or more of pedal position, pedal position rate of change, and/or driver torque demand. Next, in 912, the routine determines the override torque is greater than the torque limit for the lash crossing during nonoverride conditions. If so, the routine uses the override torque command in 914, and if not the routine uses the unmodified torque limit for the lash crossing in 916. In this way, it is possible to provide smooth torque control during transitions through the lash zone while at the same time providing rapid torque response when requested by the driver irrespective of transitions through the lash zone.
Referring now to FIG. 10, an override due to transmission shifting to be performed in STATE 2, is described. First, in 1010, the routine determines whether the transmission controller has commanded a transmission downshift after entry into STATE 2. If so, the routine continues to 1012, where the routine determines whether the downshift command override torque is greater than the torque limit for the lash crossing under the current conditions. If so, the routine continues to 1016 to use the downshift command override torque value in performing the transitions of FIG. 5. Otherwise, when either the answer at 1010 or 1012 is no, the routine continues to 1014 to use the unmodified torque limit for the lash crossing in the transitions of FIG. 5. In this way, it is possible to adjust throttle and/or spark modifications to control engine torque transitioning through the lash zone differently depending on whether a transmission shift, such as a downshift, has recently occurred or is in progress.
Referring now to FIG. 11, an additional transmission downshift override routine is described to be performed in STATE 3 of FIG. 5. First, in 1110, the routine determines whether a downshift has started such as whether the absolute value of the instantaneous transmission gear ratio minus the initial gear transmission ratio is greater than a threshold value (X). If so, the routine continues to 1114 to transition to STATE 4. Otherwise, the routine continues from 1110 to 1112 to determine whether a downshift command override torque is greater than the torque limit for lash crossing, similar to that of 1012. If so, the routine continues to 1118, to use the downshift command override torque command value for the control and/or transitions in the routine of FIG. 5. Otherwise, when the answer to 1112 is no, the routine continues 1116 to perform unmodified torque limiting in STATE 3.
Again, in this way, it is possible to account for transmission shifts, such as downshifts, that are about to occur or are occurring in performing transitions and spark/throttle torque control during transitions through the gear lash zone of FIG. 5.
As will be appreciated by one of ordinary skill in the art, the specific routines and block diagrams described below in the flowcharts may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the disclosure, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, these Figures graphically represent code to be programmed into the computer readable storage medium in controller 12.
It will be appreciated that the configurations and embodiments disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above valve can be applied in a variety of areas, including various types of engines, such as V-6, I-4, I-6, V-12, opposed 4, and other engine types.
The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

## Claims

1. A method for a vehicle powertrain with an engine and a transmission having a clutch, comprising:
transitioning through a lash region of the transmission during clutch slipping conditions in response to a driver tip-in, including first retarding ignition timing past maximum torque timing while continually increasing engine airflow until torque converter input speed is greater than torque converter output speed, and then advancing ignition timing from the retarded timing while continuing to increase engine airflow.

2. The method of claim 1 wherein said retarding and advancing of ignition timing is based on an amount of clutch slipping.

3. The method of claim 2 wherein said clutch is a torque converter clutch.

4. The method of claim 3 wherein said clutch slipping is present when said torque converter is un-locked.

5. The method of claim 4 wherein said ignition timing is adjusted based on a gear ratio of the transmission.

6. The method of claim 4 wherein said lash region is detected based on at least one of torque converter speeds and estimated engine torque.

7. A vehicle control method for a vehicle having a powertrain with an internal combustion engine and a transmission having a torque converter clutch, comprising:
transitioning through a lash region of the transmission during torque converter clutch slipping conditions in response to a driver tip-in; and
during the transition, first retarding ignition timing past maximum torque timing while increasing engine airflow and while torque converter output speed is greater than torque converter input speed, and then second, advancing ignition timing from the retarded timing while continuing to increase engine airflow and while the torque converter output speed is less than the torque converter input speed, said retarding and advancing of ignition timing based on an amount of torque converter clutch slipping.