Vehicle and engine control system and method

An engine control system controls engine torque to transition through the transmission lash zone. The transmission lash zone is determined using speed ratio across the torque converter. When near the transmission lash zone, engine torque is adjusted at a predetermined rate until the system passes through the transmission lash zone. By limiting the change of torque in this way, driveability is improved and it is possible to quickly and reliably provide negative engine torque for braking.

FIELD OF THE INVENTION
 The present invention relates to a system and method to control an internal
 combustion engine coupled to a torque converter and in particular to
 adjusting engine output to improve drive feel.
 BACKGROUND OF THE INVENTION
 Internal combustion engines must be 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. In some cases, such as during normal driving
 conditions, the desired engine torque is calculated from the amount of
 depression of an accelerator pedal. In other conditions, such as idle
 speed control, the desired engine torque is calculated based on a speed
 error between actual engine speed and a desired engine speed. Some
 attempts have been made to use this torque control architecture to improve
 driveability during deceleration conditions, such as when a driver
 releases their foot to the minimum accelerator pedal position, known to
 those skilled in the art as a tip-out. During a tip-out, the driver is
 indicating a desire for reduced engine output.
 One system that attempts to use speed control during deceleration
 conditions operates the engine in such a way as to maintain constant
 engine speed during slow moving or stopped conditions. In this system, the
 engine is controlled to a constant speed taking into account the loading
 from the torque converter. The loading from the torque converter is
 calculated based on the engine speed and turbine speed. Engine speed can
 be controlled to a constant level during deceleration to adsorb energy
 from the vehicle and assists in vehicle braking. Further, as turbine speed
 increases, the desired engine speed is reduced to provide even more engine
 braking. Such a system is described in DE 4321413A1.
 The inventors herein have recognized a disadvantage with the above
 approach. In particular, when the accelerator pedal is released and
 subsequently engaged, the prior art system exhibits poor driveability due
 transmission gears lash. For example, when the engine transitions from
 exerting a positive torque to exerting a negative torque (or being
 driven), the gears in the transmission 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, or clunk, resulting in poor driveability and customer
 dissatisfaction. In other words, the engine first exerts a positive torque
 through the torque converter onto the transmission input gears to drive
 the vehicle. Then, when using the prior art approach during deceleration,
 the engine is driven by the torque from the transmission through the
 torque converter. The transition between these to modes is the point where
 the engine is producing exactly zero engine brake torque. Then, at this
 transition point, the gears in the transmission separate because of
 inevitable transmission gear lash. When the gears again make contact, they
 do so dynamically resulting in an undesirable impact.
 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
 experienced due to the transmission lash during the zero torque
 transition.
 SUMMARY OF THE INVENTION
 An object is to provide a method for determining when the vehicle is
 operating in or near the transmission lash zone.
 The above object is achieved and disadvantages of prior approaches overcome
 by a method for estimating when a vehicle is near a transmission lash
 zone, the vehicle having an internal combustion engine coupled to a
 transmission via a torque converter having a speed ratio from torque
 converter output speed to torque converter input speed, the method
 comprising the steps of: indicating when the speed ratio is within a
 predetermined range; and determining that the vehicle is near the
 transmission lash zone in response to said indication.
 An advantage of the present invention is that it is possible to make other
 engine control features aware that the vehicle is operating in a region
 where transmission gear separation may occur. Thus, other engine control
 features can take action to minimize effects of transmission gear
 separation.
 In another aspect of the present invention, an object is to provide an
 engine output control system for easing transitions through the
 transmission lash zone.
 The above object is achieved, and problems of prior approaches overcome, by
 a vehicle control method for a vehicle having an internal combustion
 engine coupled to a torque converter, the torque converter having a speed
 ratio from torque converter output speed to torque converter input speed,
 the torque converter coupled to a transmission, the method comprising the
 steps of: indicating when the speed ratio is within a predetermined range;
 and in response to said indication, adjusting an operating parameter to
 control a change in an engine output to be less than a preselected value.
 By using signals already available it is possible to provide a real-time
 estimate of the transmission lash zone, or zero torque point. With this
 information, it is then possible to transition through the transmission
 lash zone gently by controlling engine output so that "clunk" is minimized
 and fuel economy and emissions are optimized. In other words, the present
 invention utilizes the torque converter characteristics in the following
 way. Because these measurements are readily available, adjusting engine
 output according to the present invention near the transmission lash zone
 allows much improved drive feel since the effects of gear separation are
 minimized. Further, by using turbine speed and engine speed, effects from
 road grade, vehicle mass, temperature, and other factors are inherently
 considered without complexity or addition computation.
 An advantage of the above aspect of the invention is improved driveability.
 Another advantage of the above aspect of the invention is improved customer
 satisfaction.
 Yet another advantage of the above aspect of the invention is improved fuel
 economy.
 In yet another aspect of the present invention, the above objects are
 achieved and disadvantages of prior approaches overcome by a control
 method for a vehicle having an internal combustion engine coupled to a
 transmission via a torque converter having an input speed and an output
 speed, the method comprising the steps of: determining a speed ratio
 across the torque converter based on said input speed and said output
 speed; and controlling an engine operating parameter at a preselected rate
 when said speed ratio is within a predetermined range.
 By controlling an operating parameter in this way, it is possible to gently
 pass through the transmission lash zone, thereby improving driver comfort.
 An advantage of the above aspect of the present invention is improved drive
 comfort as a results of less severe transmission gear separation.
 Other objects, features and advantages of the present invention will be
 readily appreciated by the reader of this specification.

DESCRIPTION OF AN EMBODIMENT
 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 partially engaged, the torque
 converter is said to be in an unlocked state. Turbine shaft 17 is also
 known as transmission input shaft. Transmission 15 comprises an
 electronically controlled transmission with a plurality of selectable
 discrete gear ratios. Transmission 15 also comprises various other gears,
 such as, for example, a final drive ratio (not shown). Transmission 15 is
 also coupled to tire 19 via axle 21. Tire 19 interfaces the vehicle (not
 shown) to the road 23.
 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 transmission shaft torque, or engine shaft torque from
 torque sensor 121, 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.
 Referring now to FIG. 3, a routine for detecting deceleration conditions is
 described. First, in step 310, driver actuated pedal position (PP) is
 compared with calibratable item (PP_CT), which represents the pedal
 position at which the pedal is closed. In an alternate embodiment,
 calibratable item (PP_CT) represents the pedal position below which a
 tip-out is indicated.
 Alternatively, driver desired wheel torque, which is known to those skilled
 in the art to be a function of pedal position and vehicle speed, can be
 compared with a minimum desired wheel torque clip below which deceleration
 is desired. When the answer to step 310 is YES, then in step 312, both
 engine speed (N) and turbine speed (Wt) are read. In step 314, a
 determination is made as to whether engine speed is greater than turbine
 speed. When the answer to step 314 is YES, then deceleration conditions
 have been detected as shown in step 316.
 Referring now to FIG. 4, a routine for calculating a desired engine speed
 during deceleration conditions is described. First, in step 406, a
 determination is made as to whether deceleration conditions have been
 detected. When the answer to step 406 is YES, a determination is made in
 step 408 as to whether the torque converter is in and unlocked state. When
 the answer to step 408 is YES, engine speed (N) is read and turbine speed
 (Wt) is read from turbine speed sensor 119 in step 410. Then, in step 414
 the engine is controlled based on a speed ratio, SR as described later
 herein with particular reference to FIG. 5. Speed ratio is determined as
 (SR=Wt/N) based on the turbine speed and engine speed. In other words, in
 this example, torque converter input speed is engine speed and torque
 converter output speed is turbine speed. These speed may determined in
 various other ways, such as, for example, turbine speed can be determine
 from gear ratio and vehicle speed. Also note that the speed ratio may also
 be determined as (SRalt=N/Wt). Those skilled in the art will recognized
 that the present invention can be suitably reduced to practice in view of
 this disclosure using the speed ratio calculated in either way.
 Referring now to FIG. 5, a routine for controlling an engine output, engine
 torque in this case, is described. First, in step 510, speed ratio limit
 values (SR1, SR2) are determined based on engine operating conditions. In
 a preferred embodiment, these values are calculated based on vehicle speed
 and gear ratio using calibration functions. However, various other signals
 may be used. These limit values (SR1, SR2) represent the upper and lower
 speed ratio values between which engine torque change is limited. In other
 words, according to the present invention, limit values (SR1, SR2)
 represent the upper and lower speed ratio values between which the zero
 torque transition, or transmission lash zone transition, occurs.
 Continuing with FIG. 5, in step 511, a desired engine torque (Tdes) is
 determined using methods known to those skilled in the art. For example,
 desired engine torque may be determined based on a driver command,
 traction control, idle speed control, or various other methods. Also,
 desired engine torque can be either a desired indicated engine torque, or
 a desired engine brake torque. Then, in step 512, a determination is made
 as to whether speed ratio (SR) is within limit values (SR1, SR2). When the
 answer to step 512 is YES, then the engine torque change is limited as now
 described and it is determined that the vehicle is operating near the
 transmission lash zone, or zero torque point. In step 514, a determination
 is made as to whether desired engine torque change is greater than change
 limit R1. In particular, a determination is made as to whether the
 absolute value of desired engine torque change is greater than change
 limit R1. Change limit R1 is determined based on engine operating
 conditions such as, for example, engine speed, turbine speed, vehicle
 speed, gear ratio, or other variables. In a preferred embodiment, Change
 limit R1 is determined based on vehicle speed using a calibrated function.
 Also in a preferred embodiment, a rate of change of desired engine torque
 is determined based on current desired engine torque (Tdes.sub.i),
 previous filtered desired engine torque (Tdesf.sub.i -1) and sample time
 (Dt) as:
 ##EQU1##
 When, the answer to step 514 is YES, in step 516, current filtered desired
 engine torque (Tdesf.sub.i) is set equal to current desired engine torque
 (Tdes.sub.i). Otherwise, in step 518, current filtered desired engine
 torque (Tdesf.sub.i) is calculated based on previous filtered desired
 engine torque (Tdesf,.sub.i -1) and change limit R1 as:
 ##EQU2##
 The function (sgn) is known to those skilled in the art as the sign
 function, which produces a positive unity value when the parameter
 ##EQU3##
 is positive, and a negative unity when the parameter
 ##EQU4##
 is negative. Then, from either step 516 or 518, in step 520, actual engine
 torque is controlled to filtered desired engine torque (Tdesf.sub.i).
 Those skilled in the art will recognize various methods of controlling
 actual engine torque to a desired value, such as, for example, by
 adjusting throttle position, adjusting airflow, adjusting exhaust gas
 recirculation, adjusting ignition timing, adjusting cam timing, or
 adjusting fuel injection amount.
 Those skilled in the art will recognize various other methods, in view of
 this disclosure, for limiting an engine output change. According to the
 present invention, any method can be used for limiting the engine output
 change while in or near the transmission lash zone without departing from
 the spirit and scope of the invention. For example, in an alternate
 embodiment, engine speed change can be limited while in or near the
 transmission lash zone.
 Those skilled in the art will also recognize various other methods, in view
 of this disclosure, for filtering a parameter. For example, low pass
 filters, notch filters, and various other filters can be used to limit the
 amount of change of a parameter. In other words, desired engine torque can
 be low pass filtered when speed ratio (SR) is within limits (SR1, SR2).
 In an alternative embodiment, an engine control parameter, such as a
 throttle position, may be substituted for engine torque as described in
 FIG. 6. Referring now to FIG. 6, in step 610, speed ratio limit values
 (SR1, SR2) are determined based on engine operating conditions. Then, in
 step 611, a desired throttle position (TPdes) is determined using methods
 known to those skilled in the art. For example, desired throttle position
 may be determined based on a driver command, traction control, idle speed
 control, or various other methods. Then, in step 612, a determination is
 made as to whether speed ratio (SR) is within limit values (SR1, SR2).
 When the answer to step 612 is YES, then the throttle position change is
 limited as now described. In step 614, a determination is made as to
 whether desired throttle position change is greater than change limit R2.
 Change limit R2 is determined based on engine operating conditions such
 as, for example, engine speed, turbine speed, vehicle speed, gear ratio,
 or other variables. In a preferred embodiment, Change limit R2 is
 determined based on vehicle speed using a calibrated function. Also in a
 preferred embodiment, a rate of change of desired throttle position is
 determined based on current desired throttle position (TPdes.sub.i) and
 previous filtered desired throttle position (TPdesf.sub.i-1) as:
 ##EQU5##
 When, the answer to step 614 is YES, in step 616, current filtered desired
 throttle position (TPdesf.sub.i) is set equal to current desired throttle
 position (TPdes.sub.i). Otherwise, in step 618, current filtered desired
 throttle position (TPdesf.sub.i) is calculated based on previous filtered
 desired throttle position (TPdesf.sub.i-1) and change limit R2 as:
 ##EQU6##
 Then, from either step 616 or 618, in step 620, actual throttle position is
 controlled to filtered desired throttle position (TPdesf.sub.i). Those
 skilled in the art will recognize various methods of controlling actual
 throttle position to a desired value, such as, for example, by using a
 controller based on a throttle position error signal.
 Referring now to FIGS. 7A and 7B, these graphs shows an example of
 operation according to the present invention. In this example, upper and
 lower limit values are set to (SR2=1.05, SR1=0.95). FIG. 7A shows desired
 engine torque on the vertical axis and time on the horizontal axis. The
 dashed line shows desired engine torque and the solid line shows the
 filtered desired engine torque according to the present invention. At time
 t2, the speed ratio reaches limit value SR1. From this point, the desired
 engine torque is limited to change at a maximum rate of R1. Then, the
 speed ratio reaches limit value SR2 at time t2 and the filtered desired
 engine torque again equals the desired engine torque. FIG. 7B shows the
 corresponding transmission input shaft torque (which is equal to torque
 converter output shaft torque). As transmission input shaft torque passes
 through zero torque, or the transmission lash zone, torque is changing
 slow than it would otherwise be, and transmission gear separation effects
 are minimized.
 FIGS. 7A and 7B have shown an example of operation according to the present
 invention for tip-out conditions. However, those skilled in the art will
 recognize that the present invention as described can also be used to
 advantage during tip-in maneuvers, tip-out maneuvers, or both.
 In addition to the above control methods, other features can be performed.
 In particular, when at a speed ratio of substantially one, controller 12
 has determined that the engine drivetrain is producing substantially zero
 torque, as long as the torque converter is unlocked. Thus, if torque
 sensor 121 has a tendency to drift, it can be re-zeroed in response to an
 indication that the drivetrain is producing substantially zero torque.
 This concludes the description of the Preferred Embodiment. The reading of
 it by those skilled in the art would bring to mind many other alterations
 and modifications without departing from the spirit and scope of the
 invention. For example, if turbine speed is not measured, vehicle speed
 and gear ratio can be substituted without loss of function. Accordingly,
 it is intended that the scope of the invention be limited by the following
 claims.