Abstract:
A method for controlling wheel-hop in a vehicle driveline includes detecting that a wheel-hop condition occurs upon determining an amplitude and frequency of speed oscillations of a component that transmits power to wheels of the driveline, engaging a transmission friction clutch that transmits torque in the driveline between an engine and the wheels, and modulating requested engine torque.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to the driveline of a motor vehicle, and is independent of the driven wheel configuration. For example, the motor vehicle driveline may be front wheel drive, rear wheel drive and/or all wheel drive, with or without locking differential axle(s). The invention relates more particularly to detecting and controlling wheel-hop through detection, measurement, monitoring and automatic transmission one-way clutch protection. 
         [0003]    2. Description of the Prior Art 
         [0004]    Wheel hop is an objectionable operating condition that occurs in the driveline of a motor vehicle. It is known that driveline torsional oscillations excite the vehicle at a characteristic frequency, the natural frequency of the system. Wheel hop is apparent when the driven wheels oscillate torsionally due to the driven wheels being in frictional contact with a road surface followed by the wheels losing contact (sometimes referred to as stick and slip). During a wheel hop condition, the vehicle&#39;s suspension system often oscillates torsionally producing vertical and angular displacements (sometimes referred to as wrap-up). 
         [0005]    The resulting periodic driveline impact loads generated by wheel hop can potentially exceed the design limitations of many of the driveline components. 
         [0006]    A need exists in the industry for a reliable, repetitive technique to detect, measure, monitor and protect the principal driveline components, including the automatic transmission and its internal components from damage and to avoid performance problems caused by wheel hop. 
       SUMMARY OF THE INVENTION 
       [0007]    A method for controlling wheel-hop in a vehicle driveline includes detecting that a wheel-hop condition occurs by determining an amplitude and frequency of speed oscillations of a component that transmits power to the wheels of the driveline, engaging a transmission friction clutch that transmits torque in the driveline between an engine and the wheels, and modulating requested engine torque. 
         [0008]    The friction clutch is hydraulically actuated and arranged in parallel with a one-way clutch in the driveline between the engine and the wheels. If the speed amplitude is greater than a reference speed amplitude, engine output torque transmitted to the wheels is reduced. 
         [0009]    The method protects the driveline components against torsional impact loading, improves durability of the transmission&#39;s components, and preserves the calibration benefits of non-synchronous shift events in the transmission. 
         [0010]    The method supports a control system strategy embedded in the automobile&#39;s powertrain control module, which can continuously detect, measure, monitor and protect the automatic transmission from adverse load conditions produce by wheel hop. 
         [0011]    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 
         [0012]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a top view of a motor vehicle driveline that includes a transmission, transfer case, front and rear drive shafts, and shafts extending to front wheels and rear wheels; 
           [0014]      FIG. 2  is diagram showing the logic flow of an algorithm that controls wheel hop; and 
           [0015]      FIG. 3  is a graph that shows representative speed signal oscillations produced by an output shaft speed sensor. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    With reference now to the drawings and particularly to  FIG. 1 , the powertrain  8  of a motor vehicle, to which the present invention can be applied, includes front wheels  10  and rear wheels  12 , a power transmission  14  for producing multiple forward speed ratios and reverse drive, an engine  15  driveably connected to the transmission, and a transfer case  16 , which continuously driveably connects the transmission output  17  to a rear drive shaft  18 . The transfer case  16  selectively connects the transmission output to both the front drive shaft  20  and rear drive shaft  18  when a four-wheel drive mode of operation is selected, either manually or electronically. 
         [0017]    The rear drive shaft  18  transmits power to a rear differential mechanism  22 , from which power is transmitted differentially to the rear wheels  12  through axle shafts  24 ,  26 , which are contained within a differential housing. Often the rear differential mechanism  22  is a locking differential, which under certain conditions secures the rear axle shafts  24 ,  26  mutually preventing differential drive to the rear wheels  12 . The front wheels  10  are driveably connected to right-hand and left-hand half-shafts  32 ,  34 , to which power is transmitted from the front drive shaft  20  through a front differential mechanism  36 . 
         [0018]    The transfer case assembly  16  continually transmits rotating power to the rear driveshaft  18  and rear wheels  12 , which is the primary power path. The transfer case  16  intermittently transmits rotating power through a transfer clutch and a chain mechanism  38  to the front driveshaft  20  and the front wheels  10 , which is the secondary power path. A transfer clutch, located in the transfer case  16 , is actuated and engaged to transmit power to the front driveshaft  20 . When the transfer clutch is disengaged, power is transmitted from the transmission output  17  only to the rear wheels  12 . 
         [0019]    An electronic controller for controlling operation of the engine  15 , transmission  14  and transfer case  16  comprises a microprocessor  56 , accessible through a communication network  58  to electronic memory including RAM  60 , ROM  62  and KAM  63 . An output shaft speed (OSS) sensor  50  produces a continuous electronic signal representing the variation with time of the amplitude of the speed of the transmission output shaft  17 . The speed signal is carried on line  52  to the input port  54  of the controller  56 . A signal representing the position of an accelerator pedal  66 , i.e. the degree to which the pedal is depressed, produced by sensor  68  is carried on line  70  to the controller&#39;s input port  54 . 
         [0020]    Transmission  14  includes a hydraulically-actuated friction clutch  72  and a one-way clutch  74  arranged in parallel with clutch  72 . When the transmission produces certain forward gear ratios, such as first gear, and reverse drive, rotating power is transmitted through the one-way clutch  74  to the transmission output  17 . 
         [0021]    The output port  76  of controller  56  transmits various output signals, one output signal carried on line  78  to a solenoid-actuated valve that alternately engages and disengages clutch  72 ; another signal carried on line  82 , which operates to control the magnitude of torque produced by engine  15 ; and multiple signals, which control operation of transmission  14  in its various speed ratios. 
         [0022]    The controller&#39;s ROM  64  contains an algorithm  90 , whose steps are illustrated in  FIG. 2 , which detects, controls, and modulates or eliminates wheel hop. At step  92  a test is made to determine whether certain conditions indicative of wheel hop are present. Those entry conditions include vehicle speed below a reference speed, the transmission  14  operating in a suitable gear, preferably first or second forward gear or reverse gear. 
         [0023]    If the result of test  92  is logically false, the algorithm  90  re-executes the test at step  92 . When the result of test  92  is logically true, the algorithm acquires data produced by the OSS sensor  50  data before advancing to step  102 . While the algorithm is executing its other steps, step  94 - 100  are continually, repetitively executed and the new data are updated in RAM  62 . 
         [0024]    At step  94 , a sample is taken from the signal produced by OSS sensor  50  to determine the maximum current oscillating speed of the OSS. At step  96 , the sampled amplitude and frequency of the OSS are determined. At step  98  the minimum OSS is determined from the sampled oscillating OSS signal. 
         [0025]      FIG. 3  is a graph that shows representative speed signal oscillations produced by the OSS sensor  50 . The first oscillation  104  has a first peak  106  and a second peak  108 . Similarly, the second oscillation  110  has a first peak  112  and a second peak  114 . The occurrence of double peaks can affect accuracy of data from which the signal&#39;s period, frequency and amplitude are determined. 
         [0026]    To improve accuracy of the frequency data, the algorithm establishes a calibratable reference decrease in amplitude  116  that must occur during the current oscillation following each of the peak amplitudes  106 ,  108 . When the reference decrease in amplitude  116  occurs, the immediately preceding peak is determined to be the maximum amplitude for the subject oscillation. 
         [0027]    The occurrence of double peaks can cause a large variation in the period length  118 ,  119  and the corresponding frequency that can be determined from the OSS speed signal  50 . To improve accuracy of the frequency data, the algorithm determines the period length from the same amplitude of either consecutive falling edges  120 ,  122  or consecutive rising edges  124 ,  126 , and calculates the frequency from the period length, so determined. 
         [0028]    At step  100 , a sample is taken from the signal produced by OSS sensor  50  to determine the current amplitude and frequency of the oscillating speed of the OSS as described with reference to  FIG. 3 . 
         [0029]    At step  102  a test is made to determine whether the OSS amplitude and frequency are within corresponding empirically-determined reference ranges for the subject vehicle driveline. If test  102  returns true, it indicates that oscillations of the signal produced by the OSS sensor  50  have characteristics indicative of the presence of wheel hop in the subject vehicle driveline such as amplitude, sustained cyclicality, and periodicity. The frequency of the speed signal should be within an acceptable range of the resonant torsional frequency of the subject vehicle&#39;s driveline. In a known example, that frequency range is between six and ten Hz. 
         [0030]    If the result of test  102  is true, a wheel hop oscillation counter is incremented at step  130 . If the result of test  102  is false, a wheel hop oscillation counter is decremented at step  132 . 
         [0031]    At step  134  a test is made to determine whether the current number or count of wheel hop oscillations is sufficient to conclude that a wheel hop event is occurring. If the result of test  134  is false, a test is made at  136  to determine whether conditions permitting an exit from the algorithm  90  are met. If so, execution of the algorithm terminates at step  140 . 
         [0032]    If the result of test  134  is true, at step  140  the controller causes clutch  72  to engage, thereby modulating torsional oscillations in the one-way clutch  74  and the vehicle&#39;s driveline. 
         [0033]    At step  142 , an indicator representing a change in endurance or service life of the driveline components due to the wheel hop oscillations is determined with reference to the amplitudes of the OSS signal  50  and the number of wheel hop oscillations that have occurred during the current event. Controller  56  stores the indicator in KAM  63 . 
         [0034]    At step  144  a test is made to determine whether the OSS amplitude is high enough relative to an empirically-determined reference amplitude to risk damage to the driveline components. If the result of test  144  is false, control passes to step  136 . 
         [0035]    If the result of test  144  is true, at  146  controller  56  adjusts an engine operating parameter to reduce or eliminate wheel hop. The adjusted engine operating parameter may include any engine output torque, engine airflow, engine throttle position, engine ignition timing and engine air-fuel ratio, or any combination of these parameters. Thereafter, control passes to test  136 . 
         [0036]    The exit conditions tested at step  136  include the vehicle speed being greater than a reference exit vehicle speed, accelerator pedal position being less than a reference exit pedal position for longer than a reference period, and a sustained reduction in OSS speed signal amplitude for longer than a reference period. 
         [0037]    If the result of test  136  is false, control returns to steps  94 - 100 . 
         [0038]    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.