Abstract:
A method for controlling a vehicle on an uphill incline includes automatically shifting a transmission to first gear, automatically stopping the engine, using wheel torque to maintain a one-way clutch engaged and to hold a transmission component against rotation, preventing vehicle rollback by automatically engaging a target gear and tying-up the transmission automatically restarting the engine, and automatically reengaging first gear.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to the control of a vehicle stopped on a hill, particularly to holding the vehicle against unintended rolling. 
         [0003]    2. Description of the Prior Art 
         [0004]    In micro hybrid vehicles where engine is shut down when the vehicle is stopped it is desirable to prevent the vehicle from rolling backwards when vehicle is on an uphill grade. This is particularly critical when the brake pedal is released but the engine is in the process of starting up and has not developed full torque. 
         [0005]    At the same time when the vehicle is stopped on a downhill slope it is not necessary to inhibit vehicle motion since it is common driver expectation to see vehicle rolling on the downgrade road when brakes are released. 
         [0006]    In some existing art this is accomplished through a hill hold system in which the wheel brakes are applied. These systems require grade detection, which can be challenging due to various electronic noise factors such as temperature and time drift of the grade sensor signal, and various failure modes when the sensor information is not available to the brake system. 
         [0007]    Some brake hill hold systems also require an electric pump to create either hydraulic pressure or vacuum, which maintain excessive brake pressure once the brake pedal is released. This pump depletes the vehicle battery and thus reduces potential fuel economy benefit. 
       SUMMARY OF THE INVENTION 
       [0008]    A method for controlling a vehicle on an uphill incline includes automatically shifting a transmission to first gear, automatically stopping the engine, using wheel torque to maintain a one-way clutch engaged and to hold a transmission component against rotation, preventing vehicle rollback by automatically engaging a target gear and tying-up the transmission automatically while restarting the engine, and automatically reengaging first gear. 
         [0009]    No brake intervention is required to maintain hill hold eliminating potential need for the brake vacuum supply or for the electric brake pump. 
         [0010]    Also no grade sensor, such as a tilt detection sensor, is required for the execution of the hill hold, thereby reducing the cost of the system and improving reliability. 
         [0011]    The control does not require a roll back signal or any additional controller functionality but rather relies on the directional properties of a one-way clutch. 
         [0012]    The control is robust and works very well even on very small grades. 
         [0013]    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 
         [0014]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a schematic diagram of an automatic transmission; 
           [0016]      FIG. 2  is chart showing for each gear the applied and released states of the friction control elements of the transmission of  FIG. 1 ; and 
           [0017]      FIG. 3  is a graph show the variation of various vehicle parameters as the control is performed. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Referring now to the drawings, there is illustrated in  FIG. 1  the kinematic arrangement of an automatic transmission  8 . A torque converter  10  includes an impeller wheel  12  connected to the crankshaft  14  of an internal combustion engine, a bladed turbine wheel  16 , and a bladed stator wheel  18 . The impeller, stator and turbine wheels define a toroidal fluid flow circuit, whereby the impeller  12  is hydrokinetically connected to the turbine  16 . The stator  18  is supported rotatably on a stationary stator shaft, and an overrunning brake  20  anchors the stator to the shaft to prevent rotation of the stator in a direction opposite the direction of rotation of the impeller, although free-wheeling motion in the opposite direction is permitted. 
         [0019]    The torque converter  10  includes a lockup clutch  22  located within the torque converter impeller housing  23 . When clutch  22  is engaged, the turbine  16  and impeller  12  are mechanically connected to a transmission input shaft  24 ; when clutch  22  is disengaged, the turbine  16  and impeller  12  are hydrokinetically connected and mechanically disconnected. Fluid contained in the torque converter  10  is supplied from the output of an oil pump assembly and is returned to an oil sump, to which an inlet of the pump is connected hydraulically. 
         [0020]    Transmission  8  is enclosed in a transmission housing  25 , which is fixed against rotation to the vehicle structure. The input  24  is driven by the engine through torque converter  10 . An output  27  is driveably connected to the vehicle&#39;s wheels, preferably through a differential mechanism and a set of transfer gears (not shown). 
         [0021]    The transmission  8  includes three epicyclic gearsets  26 ,  28 ,  30 . The first gearset  26  includes a first sun gear  32 , first ring gear  34 , first carrier  36 , and a first set of planet pinions  38 , supported for rotation on carrier  36  and meshing with first sun gear  32  and first ring gear  34 . Ring gear  34  is secured to carrier  36  and output  27 . 
         [0022]    The second gearset  28  includes a second sun gear  40 , second ring gear  42 , second carrier  44 , and a set of planet pinions  46 , supported for rotation on second carrier  44 . Sun gear  40  is secured to input  24 . The output  27  is supported on bearings  46  and secured to a final drive pinion  48 , which transmits torque to the ring gear (not shown) of a differential mechanism  50 . Each of the vehicle wheels  80 ,  82  is driveably connected to an output of the differential mechanism  50 . 
         [0023]    The third gearset  30  includes a sun gear  52 , ring gear  54 , carrier  56 , and a first set of planet pinions  58 , supported for rotation on carrier  56  and meshing with sun gear  52  and ring gear  54 . 
         [0024]    Transmission  8  includes two hydraulically actuated clutches  60 ,  62  and three hydraulically actuated brakes  64 ,  66 ,  68 . The hydraulically actuated clutches and brakes are sometimes referred to as friction elements or control elements. A clutch  60  selectively opens and closes a drive connection between input  24  to carrier  36  and ring gear  42 . A clutch  62  selectively opens and closes a drive connection between sun gear  32  and input  26 . A brake  64  alternately releases and holds sun gear  32  against rotation. A brake  66  alternately releases and holds carrier  36  and ring gear  42  against rotation. A brake  68  alternately releases and holds sun gear  52  against rotation. 
         [0025]    Clutches  60 ,  62  and brakes  64 ,  66 ,  68  include plates, which are connected by a spline to a first member, and friction discs, which are connected by a spline to a second member, the plates and discs being interleaved. When hydraulic pressure is applied to a servo that actuates a control element, its plates and discs are forced together into mutual frictional contact, thereby increasing the torque transmitting capacity of the control element and driveably connecting the first and second members. When hydraulic pressure is vented from the servo, the control element transmits no torque, allowing the first and second members to rotate independently. 
         [0026]    Although clutches  60 ,  62  and brakes  64 ,  66 ,  68  have been illustrated and described as hydraulically actuated multi-plate clutches and brakes, the invention may be practiced with alternate types of releasable connections including but not limited to dog clutches and brakes, controllable one way clutches and brakes, magnetically actuated clutches and brakes, or electrically actuated clutches and brakes. 
         [0027]    A mechanical one-way clutch (OWC)  70  includes an outer race  72 , secured to the housing  25 ; an inner race  74 , secured to carrier  36 ; and an element  74  that alternately engages the races  72 ,  74  and produces a drive connection between the races in one rotary direction. OWC  70  overruns or disengages, thereby releasing the inner race  74  for free rotation in the opposite direction. In this way, OWC  70  holds sun gear  42  and carrier  36  against rotation in one rotary direction and releases them to rotate freely in the opposite rotary direction. OWC  70  is arranged in parallel with brake  66  between carrier  36  and housing  25 . 
         [0028]    As the table of  FIG. 2  shows, first gear is produced by engaging brake  68 . OWC  70  is engaged. When brake  66  is engaged, first gear has engine braking; when brake  66  is disengaged, first gear does not have the engine braking. 
         [0029]    Second gear is produced by concurrently engaging brakes  64  and  68 . OWC  70  overruns in each of the forward gears other than first gear. Third gear is produced by concurrently engaging brake  68  and clutch  62 . Fourth gear is produced by concurrently engaging brake  68  and clutch  60 . Fifth gear is produced by engaging clutches  60  and  62 . Sixth gear is produced by concurrently engaging brake  64  and clutch  60 . Reverse gear is produced by concurrently engaging brake  66  and clutch  62 . 
         [0030]    When the vehicle is stopped in first gear on a hill having positive slope, negative wheel torque produced by the weight of the vehicle is transmitted from wheels  80 ,  82  through the final drive mechanism  84  and transmission gearing, toward the input  24  and engine.  FIG. 3  shows wheel brake pressure  90  increasing as the brake pedal is applied and engine speed  92  decreasing when the engine is turned off automatically by an electronic engine control unit (ECU)  94  at  95 . This wheel torque locks OWC  70 , causing it to produce a drive connection between carrier  36  and housing  25  and a torsion reaction to the negative wheel torque. 
         [0031]    If under these conditions, transmission  8  shifts from the current gear, first gear, to another gear, the target gear, while the vehicle is stopped in first gear with the engine off on a hill having positive slope, as might occur in response to a commands from an electronic transmission control unit (TCU)  93 , the state of engagement of clutches  60 ,  62  and brakes  64 ,  66 ,  68  corresponding to the target gear and the locked OWC  70  will cause transmission  8  to tie-up and will stop the vehicle from rolling backwards on the uphill incline. 
         [0032]    Under these conditions,  FIG. 3  shows an upshift at  96  to third gear, in which clutch  62  and brake  68  are engaged, OWC remains engage and brake  66  becomes disengaged. Due to the concurrent engagement of OWC  70 , clutch  62  and brake  68 , transmission  8  becomes tied-up, thereby preventing the vehicle from rolling backward down the hill. 
         [0033]    Because of the directional properties of OWC  70 , the transmission is not tied-up when the vehicle is stopped on a hill with negative slope. Instead the positive wheel torque produced by the weight of the vehicle unlocks OWC  70 . 
         [0034]      FIG. 3  shows that the vehicle operator having released the wheel brakes at  98 , and the engine having been restarted automatically at  100  by the ECU  94 . At  102 , the transmission is shifted into first gear, thereby engaging brakes  66  and  68 . Engine torque propels the vehicle forward preventing rollback  104  on the uphill grade. 
         [0035]    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.