Abstract:
A method for controlling a clutch driveably connected to an engine and vehicle wheels includes stopping fuel supply to an engine cylinder, provided a misfire occurs in the cylinder, producing slip across the clutch, resuming fuel supply to the engine cylinder, provided engine speed and engine load remain below reference limits, and adjusting a state of the clutch without reference to engine misfiring.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a method for controlling slip of a toque convertor bypass clutch such that the clutch dampens powertrain vibrations caused by engine misfiring. 
     2. Description of the Prior Art 
     Spark ignition gasoline engines sometimes have engine misfires. Government regulations allow the fuel supply to the misfiring cylinders to be shut off to prevent high emissions output and potential thermal damage to the catalyst emissions system. Government regulations also require that a malfunction light be illuminated when engine misfiring occurs. 
     Depending on the number of engine cylinders that are misfiring and the number of cylinders shut off during failure mode management (FMM), the engine and vehicle can shake from the uneven torque pulses by only operating a portion of the total cylinders. 
     Operating with excessive shake or under poor noise, vibration and harshness (NVH) conditions is to be avoided. 
     SUMMARY OF THE INVENTION 
     A method for controlling a clutch driveably connected to an engine and vehicle wheels includes stopping fuel supply to an engine cylinder, provided a misfire occurs in the cylinder, producing slip across the clutch, resuming fuel supply to the engine cylinder, provided engine speed and engine load remain below reference limits, and adjusting a state of the clutch without reference to engine misfiring. 
     The method allows NVH damping, whereas leaving the torque convertor bypass clutch fully engaged or locked mode transmits undesirable vibration to the driveline. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram showing a torque converter located in a vehicle powertrain; and 
         FIG. 2  is logic flow diagram of a control algorithm. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the cross-sectional view seen in  FIG. 2 , numeral  10  designates a hydrokinetic torque converter and numeral  12  designates a compound planetary gear unit. The torque converter  10  and gear unit  12  are located in a transmission housing  13 . 
     The torque converter  10  includes a bladed impeller  16 , a bladed turbine  18 , and a bladed stator  20 . Stator  20  is mounted on a one-way brake  32  and is supported by stationary turbine sleeve shaft  34 . 
     The converter elements  16 ,  18  and  20  form a toroidal fluid flow path in known fashion, whereby impeller torque is multiplied hydrokinetically to produce a turbine torque that is distributed through turbine hub  22  to the turbine shaft  24 . The impeller  16  is enclosed within an impeller housing  26 , which is bolted to the crankshaft  28  an internal combustion engine  29 . The bolts are located at the hub of a drive plate  30 , the latter being secured to the outer periphery of the impeller housing  26 . Engine  29  includes multiple cylinders  36 ,  37 ,  38 ,  39 . 
     A torque converter bypass clutch  42  includes a clutch plate  44  adapted to engage the adjacent wall of the impeller housing  26 . Plate  44  is secured to turbine hub  22  by means of a damper assembly  46 . Fluid is distributed radially outward through the space between the clutch plate  44  and the adjacent wall of the impeller housing when the clutch is disengaged. The torque converter  10  at that time acts as an open converter and is capable of multiplying torque hydrokinetically. Fluid is supplied continuously to the toroidal cavity of the converter and the pressure thus developed applies the clutch by engaging the clutch plate  44  against the adjacent frictions surface of the impeller housing. The radial outward flow through the space between the plate  44  and the adjacent wall of the impeller housing is interrupted when the clutch is applied. 
     The transmission output  50  is driveably connected to the driven wheels  52 ,  53  of the vehicle. 
     During FMM, opening the torque convertor clutch  42  or controlling slip across the torque convertor clutch  42  partially decouples (creates a viscous damper) between the engine  29  and the wheels  52 . Either opening clutch  42  or controlling its slip ratio as a function of the number of firing cylinders of engine  29  allows damping of torsional vibration from the engine  29  through the driveline and stops the vehicle shaking and poor vehicle NVH. 
     The logic flow diagram  60  of  FIG. 2  represents an algorithm for controlling bypass clutch  42 . At step  62 , on-board diagnostics detects a high rate of engine misfiring, greater than a limit rate that would damage a catalytic converter on-board the vehicle. Various techniques for determining engine misfiring includes crankshaft-based acceleration that measures acceleration input to the crankshaft from each cylinder torque pulse This can&#39;t happen if convertor is locked, spark plug ionization, and use of an in-cylinder pressure transducer whose pressure signal can be used to detect misfiring. 
     At step  64 , an engine misfire monitor invokes failure mode mitigation such as fuel cut-off to any of the misfiring cylinders of engine  29 , open-loop air fuel control and limiting engine load and torque output by the engine. 
     At step  66 , a test is made to determine whether fuel cut-off to at least one of the engine cylinders has occurred. If the result of test  66  is logically false, at step  68  execution of the algorithm ends. 
     If the result of test  66  is true, at step  70  a desired slip across bypass clutch  42  is determined as a function of such variable that may include the number of cylinders to which fuel is shut-off, the relation between cylinder firing sequence and the shut-off cylinders, engine speed, engine load, the current gear in which transmission gear unit  12  is operating, temperature of automatic transmission fluid (ATF) in gear unit  12 , etc. For example, the desired slip across clutch  42  would be greater if the misfiring cylinders were consecutive in the firing order rather than if such cylinders were separated mutually in the firing order. 
     At step  72  a controller that controls the engaged, disengaged and slipping state of clutch  42  arbitrates the relative importance of the desired slip produced at step  70  with other converter clutch slip requests  74  in support of gear shift events, transmission component production, etc. 
     At step  76 , the controller of clutch  42  produces a signal representing the arbitrated clutch slip limit. In response to that signal, a solenoid actuates a valve, which produces hydraulic pressure in the torque converter corresponding to the magnitude of the clutch slip limit. 
     At step  78 , a test is made to determine whether a first timer, which counts up during a first period, has expired, the first period preferably having a length of 30 seconds immediately following the beginning of engine misfiring. If the result of test  78  is logically false, at step  80  that timer is incremented to the length of the first period, and control returns to step  70  awaiting expiration of the first timer. 
     When the result of test  78  is true, at step  82  the first timer is latched at the time limit of the first timer. 
     At step  84 , a test is made to determine whether engine speed and engine load have decreased to acceptable magnitudes that would allow unlatching the failure mode mitigation actions. If the result of test  84  is false, at step  86  a second timer is reset to zero awaiting a tip-out event, and control returns to step  70 . 
     If the result of test  84  is true, at step  88  a test is made to determine whether the second timer has expired. Preferably the second timer is set to a few seconds only. If the result of test  88  is false, at step  90  a second timer is incremented awaiting the second timer to expire, and control returns to step  70 . 
     If the result of test  88  is true, indicating that engine speed and load have reduced to lower magnitudes and remained low for at least the length of the reference period of the second timer, at step  92  fuel supply to the cut-off engine cylinders is restored, the state of bypass clutch  42  is reestablished and produced without reference to engine misfiring, and execution of the algorithm ends. 
     Steps  84 ,  86 ,  88  and  90  comprise a period during which the clutch controller awaits engine operating conditions to return to acceptable levels before resupplying fuel to the misfiring cylinders of engine  29 . 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.