BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is diagrammatic view of an exemplary vehicle powertrain including an electronic control module for controlling the operation of the engine in response to a driver demand signal, in accordance with the invention;
FIG. 2 is a flow chart illustrating the main steps of an exemplary method for determining when the manual transmission of a vehicle powertrain is placed “in gear” by the vehicle's driver and, further, when a transmission shift is otherwise deemed to be “in progress,” in accordance with aspects of the invention;
FIGS. 3A-3E are a first set of correlated plots of engine speed, vehicle speed, and the product of vehicle speed, the nominal gearset gear ratio, and the pinion factor; of the determined transmission shift-in progress flag; of the determined effective transmission gear ratio; of the detected driver demand signal, as represented by the output of a pedal position sensor; and of the unfiltered and filtered requested torque signals, all versus time;
FIG. 3F is an enlarged view within Circle 3F of FIG. 3E, again showing unfiltered and filtered requested torque signals versus time; and
FIGS. 4A-4D are a second set of correlated plots of the determined effective gear ratio and the tolerance band associated with the fourth gear ratio, the determined transmission shift-in progress flag, the driver demand signal, and the unfiltered and filtered requested torque signals, all versus time, during a single manual declutching event after the manual transmission has been operating in fourth gear.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the Drawings, FIG. 1 is a diagrammatic view of an exemplary powertrain 10 for a motor vehicle that includes an electronic control module (“controller 12”) for controlling the operation of an engine 14 based at least in part on a driver demand signal generated by an accelerator pedal position sensor 16, and a manual transmission 18 including several available gears by which the driver selectively couples the engine's output shaft to a driven vehicle wheel 20, either directly through a vehicle differential 22 coupling the transmission's output shaft 24 to the driven wheel's half-shaft 26 or, as seen in FIG. 1, indirectly through a driver-selectable reducing gearset of a transfer case 28. A suitable engine speed sensor 30 and at least on wheel speed sensor 32 generate respective signals from which the controller determines values N, V representative of the current engine speed and current vehicle speed, respectively.
FIG. 2 illustrates the main steps of an exemplary method 34, for use with a vehicle powertrain having a manual transmission such as the one illustrated diagrammatically in FIG. 1, to determine both when the driver has initiated a transmission gear shift (also referred to herein a “shift in progress”), and when the transmission 18 has either been shifted by the driver into a selected one of the transmission's several available gearsets, or has been placed “in neutral.”
As seen in FIG. 2, the exemplary method 34 includes determining, at step 36, the speed of the transmission's output shaft 24 based on a previously-stored value for the differential's pinion factor (or, in the case of an engaged transfer case operating with its “low” gearset, the resulting effective pinion factor Rp), and the current value V for the vehicle speed, as determined by the controller 12 based upon the signal generated by the wheel sensor 32. The method 34 further includes determining whether the resulting effective transmission gear ratio is within a predetermined tolerance of one of the known gear ratios for the transmission 18. While the invention contemplates use of any suitable tolerances, either fixed or variable, including different preferably-calibratable tolerances bracketing each nominal transmission gear ratio, by which to infer an “in-gear” or “shift in progress” state of the transmission 18, in a preferred method, the tolerances are conveniently defined as plus-or-minus five percent (±5%) of the nominal gear ratio for each of the transmission's gearsets. If is determined, at step 40, that the effective transmission gear ratio is not within the tolerance band defined around any predetermined transmission gear ratio, at step 46, the flag SHIFT_IN_PROGRESS is set to logical one (indicating that a transmission shift is, indeed, “in progress”). At step 50, the method includes filtering the torque request signal using the filter coefficient, for example, when the driver demand signal drops rapidly below a predetermined value corresponding to a relatively-low positive generated brake torque (as described further below), in order to reduce the likelihood of drivetrain “clunk.” While the invention contemplates filtering the torque request signal in any suitable manner, in the exemplary method 34, the filtered requested torque signal τR′ is calculated as follows:
τR′=Cƒ×τR+(1−C71)×τR′
wherein:
- τR is the unfiltered requested torque signal; and
- Cƒ is a previously-stored value for the filter coefficient ranging between zero and one, selected, for example, from several previously-stored values based on a determination of the previously “matched” gear.
Referring to the correlated set of plots of FIGS. 3A-3E, FIG. 3A is a plot of the engine speed N, the resulting vehicle speed V, and the product of vehicle speed V, nominal gearset gear ratio R1 through R4, and pinion factor Rp, all versus time t, as a vehicle driver “tips-in” and clutches the manual transmission 18 at time t0 to launch the vehicle in first gear (R1), then through several tip-outs and declutching/clutching events as the driver runs up through second (R2), third (R3), and, ultimately, into fourth gear (R4), at times t1 through t8. FIG. 3A also includes an overlying plot of vehicle velocity V, for reference purposes. FIG. 3B shows the set value of the determined flag SHIFT_IN_PROGRESS, as the driver declutches and clutches through the several transmission gears R1 through R4. FIG. 3C is a plot of the effective transmission gear ratio Re, calculated as the engine speed N divided by the product of the vehicle speed V and the pinion factor Rp (from which the currently-selected transmission gearset is identified, as further described in connection with FIG. 4A below), versus time t, the periodic plateaus, for example, between times t4 and t5, and again between times t6 and t7 clearly correlate to the full engagement of an identifiable transmission gearset (specifically, in second gear between times t4 and t5, and in third gear between times t6 and t7).
FIG. 3D is a plot of the driver demand signal, as represented by the output PPS of a pedal position sensor 16, from which the requested torque signal τR is generated. FIG. 3E, as well as enlarged FIG. 3F, shows the resulting generated torque request signal τR (in broken line) and a filtered requested torque signal τR′, each versus time t, illustrated the effect of the use of the filter coefficient Cƒin ordinarily smoothing the requested torque transitions to improve vehicle NVH. As best seen in FIG. 3F, in a preferred embodiment, the requested torque signal τR is filtered in response to a pedal tip-out only once the requested torque signal τR has dropped below a predetermined value τinit_fil, wherein the predetermined value τinit_fil is a calibratable value representative of a minimum positive generated brake torque that will take up the mechanical lash in the drivetrain. In this manner, the method 34 advantageously provides a rapid engine torque to changes in sensed driver demand while reducing the likelihood of drivetrain clunk in response to a close-pedal input.
Referring to FIGS. 4A-4D, during a single manual declutching event following a pedal tip-out when driving, for example, in fourth gear (R4), it will be seen that as the output signal PPS generated by the pedal position sensor 16 rapidly drops to a minimum value upon pedal tip-out at time t9, the generated requested torque signal τR (in broken line) is filtered using the appropriate calibratable filter coefficient corresponding to fourth gear to thereby provide a smoothed torque request signal τR′ (shown in solid line). However, at time t10, when the effective transmission ratio Re, as seen in FIG.4A, exceeds the upper value of the corresponding fourth-gear tolerance band (R4+ΔR, wherein ΔR is equal, for example, to five percent (5%) of the nominal fourth gear ratio R4), the controller 12 sets the filter coefficient to 1.0 to nullify or cancel signal smoothing, whreeupon the filtered requested torque signal τR drops immediately to its unfiltered (minimum) value τR to thereby reduce the potential for unintended engine speed flare. It will be appreciated that, by nullifying signal smoothing when a declutching event follows a throttle tip-out, the invention advantageously permits use of relatively-aggressive tip-out filtering of the requested torque signal τinit_fil, while otherwise avoiding the unintended engine speed or transient torque flares upon declutching.
Referring again to FIGS. 4A-4D, as the vehicle speed begins to drop after the declutching, the effective transmission gear ratio Re ultimately falls back into the fourth gear tolerance band at time t11, whereupon the controller 12 sets the flag SHIFT_IN_PROGRESS to logical zero, determines the selected gear (in this case, fourth gear), and sets the filter coefficient Cƒ back to the stored value corresponding to fourth gear. Then, at time t12, the effective transmission gear ratio Re ultimately falls below the lower value of the corresponding fourth-gear tolerance band (R4-ΔR), whereupon the controller 12 again sets the flag SHIFT_IN_PROGRESS to logical one and the filter coefficient Cƒ to 1.0.
In accordance with yet another aspect of the invention, the flag SHIFT_IN_PROGRESS can advantageously be used to identify when the transmission has been placed in a neutral state. By way of example only, and referring again to FIGS. 4A-4D, in the exemplary method 34, if the time period between time t10 and time t11 exceeds a predetermined minimum time period tmin, the controller 12 declares the transmission in a neutral state. While any suitable predetermined minimum time period tmin may be used, in the exemplary method 34, the controller 12 declares a neutral state if the flag SHIFT_IN_PROGRESS remains “high” for about two seconds (2 sec). While the identification of the neutral state can be used for any suitable purpose, in a preferred method, once neutral is declared. If the current engine speed is below a predetermined threshold (e.g., 2500 RPM), the controller 12 advantageously regards the transmission as remaining in neutral until both the driver “tips in” and the effective transmission ratio once again falls within a tolerance band corresponding to one of the transmissions gearsets. If the current engine speed is equal to or greater than the predetermined threshold, the controller 12 will permit an exit from neutral even when the pedal is in a closed position, for example, to accommodate engine downshifts when the vehicle is proceeding down a grade.
Additionally, in the exemplary method 34, the controller 12 advantageously modifies the requested torque signal as generated from the driver demand signal (as represented by the output PPS of the pedal position sensor 16) when the neutral transmission state has been declared. By way of example only, in the exemplary method 34, the controller 12 reduces the minimum value τmin for the requested torque signal when the transmission 18 is determined to be in a neutral state, to provide an additional assurance that the engine speed will appropriately drop to idle when in neutral. The invention further contemplates determining the minimum value τmin for the requested torque signal based upon the “matched” gear to similarly improve vehicle drivability.
Finally, the exemplary method 34 advantageously includes updating the stored value for the pinion factor (or, the effective pinion factor), as determined by the controller 12 based on the engine speed and the vehicle speed when the it has been otherwise determined that the transmission is operating in a specific gearset, most preferably, the transmission's top-gear-ratio gearset (as operation in the top-gear-ratio gearset is most readily differentiated from the transmission's neutral state). In this way, the exemplary method 34 takes advantage of the learned top-gear ratio of the engine speed to vehicle speed to thereby require only one unique calibration per transmission, and to thereby obviate the need for any axle- and tire-specific calibration. And, by using the effective transmission gear ratio to determine whether a transmission shift is in progress, the method of the invention can advantageously be employed in a vehicle powertrain that includes a transfer case, simply by determining the effective pinion factor that is achieved when the transfer case is switched into “low” gear.
While the above description constitutes the preferred embodiment, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims.
Patent Application
20070289400
