Abstract:
A method of engaging and disengaging transmission gears in a vehicle is provided. An intent switch is actuated for preparing the transmission to engage or disengage the transmission gears. An engine speed synchronization (ESS) controller processes an input torque parameter representing torque from an engine and an output torque parameter representing torque at a transmission output shaft. The input torque parameter may include such inputs as friction torque while the output torque parameter may include such inputs as vehicle torque load. The input torque parameter is adjusted to approximate the output torque parameter for achieving a zero torque load between the engine and transmission output shaft to facilitate engaging and disengaging transmission gears.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an engine control that breaks the torque lock typically found in a transmission with engaged gears, allowing the transmission to be moved to neutral without actuating the clutch. 
     Heavy vehicles, such as trucks have an engine driving the wheels of a vehicle through a multi-speed transmission. The transmission is moveable through several speed ratios at the control of a manual input switch. 
     A manual transmission typically slides a clutch collar relative to different gears to engage one of the gears. To complete a shift, the operator must first typically move the gear that is presently-engaged out of engagement to a “neutral” position. In some transmissions, the movement out of engagement is performed by a hydraulic piston. In the “neutral” position, the transmission does not engage any gear, and thus rotational drive is not transmitted to the transmission output shaft from the engine crank shaft. 
     This movement from an engaged position to a neutral position occurs while drive force from the engine is being transmitted. When the transmission is engaged and rotational drive is being transmitted from the engine to the transmission, there is a large torque load holding the gears and the clutch collar together at a particular axial position. This torque load makes it quite difficult for an operator, or the piston, to move the clutch collar out of engagement. This so-called “torque lock” typically makes it impossible to move a transmission to neutral without somehow reducing the torque load. To this end, vehicles with manual transmissions have historically been equipped with clutches. An operator actuates the clutch which breaks the coupling between the engine and the transmission. The torque load goes to zero, and the operator is able to move the gear out of engagement. 
     In the heavy vehicle industry, the operation historically necessary to complete a shift between gears is relatively complicated. Typically, a driver must actuate the clutch, and then begin modifying the engine speed through the accelerator to synchronize engine speed to a speed necessary for the next speed ratio to be engaged. At the same time, the operator must manually move the gear shift lever to engage the gear in the proper new gear. These procedures become more burdensome when a driver is rapidly shifting through several sequential gear changes. 
     Control devices have been developed which calculate the transmission output torque and the engine input torque and then adjust the engine input torque until it matches the transmission output torque. When the torques match, the torque load is zero and a shift may be made without clutching or manipulating the accelerator or brakes for a “clutchless” shift. 
     The calculations that the control device has typically processed to achieve this result have been rather complex, requiring the use of many inputs and processing space. Also the control devices sometimes cannot be integrated into the main engine controller, and as a result, the number of inputs available and the processor size is reduced. To this end, it is desirable to provide a more simplified calculation while maintaining or improving upon the accuracy produced by prior control devices. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The present invention provides a method of engaging and disengaging transmission gears in a vehicle. An intent switch is actuated for preparing the transmission to engage or disengage the transmission gears. A controller processes an input torque parameter representing torque from an engine and an output torque parameter representing torque at a transmission output shaft. The input torque parameter may include such inputs as friction torque while the output torque parameter may include such inputs as vehicle torque load. The input torque parameter is adjusted to approximate the output torque parameter for achieving a zero torque load between the engine and transmission output shaft to facilitate engaging and disengaging transmission gears. 
     Accordingly, the above method provides a simplified but accurate manner by which to obtain a zero torque load at the interface between the engine and transmission so that transmission shift may be effectuated without manipulating the accelerator, clutch, or brakes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1A is a schematic view of a drive system for a vehicle including a transmission; 
     FIG. 1B shows a transmission of the system in FIG. 1A in neutral; 
     FIG. 2 is a schematic view of the drive system in FIG. 1A in a vehicle; 
     FIG. 3 is a graph of the vehicle forces during a shift; and 
     FIG. 4 is a graph of the torque elimination feature of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A drive train for a vehicle is illustrated generally at  20  in FIG.  1 A. An engine  22  includes an electronic control unit  24  which controls the output speed of the engine. Control  24  will typically control the amount of fuel delivered to the engine to regulate the output speed and torque. Engine  22  has an output shaft  23  that passes through a clutch  26  to drive a multi-speed transmission  28 . The transmission  28  may be of any type known in the art. 
     A manual stick shift  30  is operable to shift the transmission  28  between any one of several speed ratios. Transmission  28  includes a gear  32  which is driven by the output of the engine  22  when the clutch  26  is closed to a transmission input shaft  27 . Gear  32  is coupled to an input shaft  27  which engages and drives a pair of gears  36  each mounted on a countershaft  37 . Only one gear  36  and countershaft  37  are shown. While a transmission is shown wherein one must move the stick shift, the invention does extend to manual transmissions wherein a piston and cylinder drive the gears after the operator requests a shift. 
     Countershaft  37  rotates several gears  38 , only two of which are shown. Gears  38  engage and rotate a plurality of gears  39  that are mounted to freely rotate on a main output shaft  40 . A shift yoke  42  slides a shift collar  44  as directed by the vehicle operator to change the speed ratio of the transmission  28 . In the illustrated transmission, collar  44  is internally splined to rotate with shaft  40 , but may slide axially along shaft  40 . Collar  44  also has external teeth  45  that are selectively received within an inner peripheral bore on a gear  39 . When the shift collar  44  is in the position shown in FIG. 1A, the teeth  45  engage the gear  39  such that the gear  39  rotates the collar  44 , and hence the shaft  40 . Thus, in the position shown in FIG. 1A, the engine drives the gear  32 , which drives gears  36  and counter-shafts  37 . The counter-shafts  37  drive the gears  38 , which drive the gears  39 . 
     Since the collar  44  is engaged to rotate with one gear  39 , then the shaft  40  will be rotated at a speed which is dependent on the gear reduction at the selected gear  39 . When one wishes to shift the transmission to another speed, another gear  39  is selected and engaged. By varying the gear reductions between the several gears  39 , transmission  28  is able to selectively achieve several distinct output speed ratios for shaft  40  relative to input from engine  22 . 
     In moving the collar  44  to shift to another speed ratio, the initial step is to move the teeth  45  out of engagement from the inner peripheral bore of the gear  39 . When the drive train  20  is transmitting rotation to the shaft  40  through the arrangement as shown in FIG. 1A, however, there is a high torque load on the connection between the teeth  45  and the gear  39  and between collar  44  and shaft  40 . This high torque load makes it difficult, if not impossible, to slide the collar  44  relative to the gear  39 . For this reason, vehicles have traditionally incorporated a clutch  26 . An operator who wishes to shift a transmission to a new speed, initially actuates the clutch. This breaks the torque transmission discussed above, and allows the operator to disengage the transmission and move to neutral. 
     As discussed above, the prior art allows an operator to shift the transmission to a new speed without operating the clutch. To achieve the ability to shift the gear without clutching a switch  48  is incorporated on the shift knob  30 . This switch  48  is utilized to request torque elimination or to eliminate the torque lock preventing sliding movement of the collar  44  from the position shown in FIG.  1 A. The collar  44  may be actuated by either the driver manipulating the shift knob or by a automatic shifting system utilizing hydraulic or pneumatic shifting mechanisms. 
     The present invention utilizes an engine speed synchronization (ESS) controller  50  to interconnect the switch  48  to the engine controller  24 . When an operator actuates switch  48 , a signal is sent to ESS controller  50  requesting a zero torque load on the connection between the engine  22  and transmission  28 . The ESS controller  50  obtains the input and output torques of the transmission and adjusts the input torque to match the output torque. 
     More specifically, the transmission input torque represents the engine output torque and is received from the engine controller  24 . The transmission output torque is a calculated value representing vehicle torque load that is based upon the calculations and assumption explained in more detail below. 
     As mentioned above, the present invention improves upon the prior art by utilizing the vehicle torque load and comparing the vehicle torque load to the friction torque from the engine. The friction torque is then changed until it closely approximates the vehicle torque and the torque at the engine/transmission interface equals zero. Vehicle torque load has not been used in the prior art to predict zero torque load for “clutchless” shifting. Utilizing vehicle torque load provides an effective and simplified means for accurately predicting zero torque. The above relationship may be represented by the following equation: 
     
       
         ZeroTorque=FrictionTorque+VehicleTorqueLoad+DitherTorque(optional). 
       
     
     The friction torque is the torque produced by the engine  22  and transmitted to the transmission  28  through clutch  26  at the transmission input shaft  27 . The friction torque is received by the ESS controller  50  from the engine controller  24  as an already processed value and is in not adjusted unless the parameter becomes stale or limits are exceeded. The friction torque value received takes parasitic losses into account and should accurately reflect the friction torque required to maintain the engine at a constant speed at the current RPM and with no torque produced at the transmission input. As mentioned above, the friction torque represents the torque being applied to the input shaft  27  of the transmission  28 . 
     Vehicle torque load is the torque applied at the transmission output shaft  40 . As stated earlier, it is the differential in torque between the transmission input  27  and output  40  shafts that creates torque lock. The vehicle torque load is highly dependent on the speed of the vehicle. However, it may be more desirable instead to use the overall gear ratio since the vehicle speed includes undesirable noise that is preferably filtered out. Overall gear ratio corresponds roughly with the vehicle speed. Using either vehicle speed or overall gear ratio, the vehicle torque load may be represented the equation 
     
       
         VehicleTorqueLoad=a+bx+cx 2 , 
       
     
     where x is either vehicle speed or overall gear ratio. Drag force, or the cx 2  term, is the most dominant portion of the equation, while the bx term corresponds to the less dominant inertial forces and the a term corresponds to the even less dominant drive forces. Vehicle torque load may also be represented by summing the torques being exerted on either side of the transmission at the input and output shafts, which is as follows: 
     
       
         VehicleForceLoad=(DriveForce−InertialForce−DragForce). 
       
     
     Vehicle force load can then be converted to vehicle torque load. 
     Drive forces include engine torque produced by the engine to propel the vehicle. Inertial forces include all the drive train inertias, such as engine, transmission, drive line, axle, and wheel inertias. Drag forces include the force produced by the vehicle&#39;s acceleration, aerodynamic drag, rolling resistance, and grade resistance and equation. These force loads may be represented by the equation            VehicleForceLoad   =           (           ActualEngineTorque   ×     OverallGearRatio   2     ×             DrivetrainEfficiency         )                  WheelRadius     -         [               (       I   eng     +     I   trans       )     ×     OverallGearRatio   2       +                   I   drive     ×     AxleRatio   2       +     I   wheels             ]     ×   a       WheelRadius   2       -     F   aero     -     F   rr     -     F   grade         ,                      where:                             I   eng     =     Engine   mass   moment   of   inertia               F   rr     =     Rolling   Resistance.                   I   trans     =     Transmission   mass   moment   of   inertia             a   =     Vehicle   Acceleration                   I   drive     =     Driveline/Axle   mass  moment   of  inertia               F   grade     =     Grade   Resistance                   F   aero     =     Aerodynamic   Drag                                                             
     The present invention may also be better understood by reference to FIG. 2 with the above variable indicated therein. A vehicle  60  is shown at  60  travelling up a slight incline. As can be appreciated by the above equations and FIG. 2, the engine must overcome all the inertial and drag forces to propel the vehicle. During operation of the vehicle, the variables that make up these forces are constantly changing and can be very difficult to determine accurately. Knowing the value of these variables is necessary so that the engine force may be adjusted to equal the actual inertial and drag forces the vehicle is experiencing in a given situation. Once engine force equals the inertial and drag forces combined, zero torque is achieved and the driver may effectuate a “clutchless” gear shift. 
     Calculating zero torque requires that many different variables be input into the processor and that processor size be sufficient to make the necessary calculations. Moreover, as previously mentioned, the values of many of the variables are difficult to obtain. The present invention uses certain assumptions to simplify the calculation while maintaining an acceptable degree of accuracy. Since the intent switch takes throttle control away from the driver thereby preventing any further acceleration of the vehicle, it may be assumed that the acceleration of the vehicle is zero and that the vehicle is coasting. This assumption simplifies the calculations required by the ESS controller by reducing the amount of information needed to accurately predict vehicle torque because the drive forces and inertial forces drop out of the above equation yielding:        VehicleTorqueLoad   =     -                      (       F   aero     +     F   rr     +     F   grade       )     ×   WheelRadius       OverallGearRatio   2       .                              
     As mentioned above, the vehicle speed may be used instead of the overall gear ratio, but overall gear ratio is preferred. 
     Referring now to FIG. 3, a graph of the vehicle velocity versus vehicle force is shown assuming zero acceleration on a level surface. Under these conditions the grade resistance and vehicle acceleration forces are zero. As seen by the graph, the aerodynamic resistance is the dominant force since it is highly dependent on vehicle velocity. Aerodynamic resistance data is determined for each vehicle in a testing facility and is embodied in a first table of vehicle test data for use by the ESS controller. Although assumed to be zero in the graph, grade resistance may be obtained from a second table of data which makes estimates based upon several factors such as throttle position and velocity. For example, if the engine is at wide open throttle and the increase in velocity is negligible then it is likely that the vehicle is traveling up an incline. Rolling resistance may be obtained from a third table of data which makes estimates based upon vehicle weight and the number of wheels bearing the vehicle&#39;s weight. As seen in FIG. 2, rolling resistance is generally constant. 
     For all the variables which are not derived from real time vehicle condition or information from tables of test data, an estimate is made to closely approximate the actual vehicle condition while minimizing the amount of dithering to achieve zero torque. 
     Referring to FIG. 4, the dither factor incorporates a variation of the input or engine torque above and below the predicted value of the vehicle torque load as discussed above. 
     Preferably, the dither value varies a small percentage of the predicted value both below and above the predicted value. Most preferably, the dither is incorporated into the engine fueling in a saw tooth fashion, such that the engine speed begins on one side of the predicted value, moving up from the greatest amount of dither to cross the predicted engine speed, and then continues on a single slope to the other extreme. The engine fueling then returns to the initial point such that the profile of the engine fueling has a ramp on a front end and then a direct downward component on the other end as shown in FIG.  4 . In this way, the profile will cross the actual zero torque value more frequently. 
     Preferably, the dither factor is only utilized when one gets close to the predicted value. As one alternative, a “blip” may be utilized immediately after receipt of the request for torque elimination. The blip would increase the torque load momentarily, then drop the torque load down to include the dither value and the transition towards the predicted zero torque value. This blip would assist in moving the system to a condition such that the zero torque value would not require a negative fueling. A negative fueling is of course not possible, and thus by utilizing the blip, the possibility of a negative fueling requirement may be eliminated. 
     Thus, an operator requests the torque elimination feature through button  48 . The ESS controller  50  makes the calculations based on the input and output parameters discussed above and instructs the engine controller  24  to vary the engine fueling as shown in FIG.  4 . The operator applies force to the manual stick shift  30 , attempting to move the collar  14  and disengage the gear. As the actual engine fueling saw tooth profile crosses the actual zero torque value, the operator will be able to disengage the collar. A signal is then sent to the controller  24  that the transmission is in neutral. Once a signal is received that the transmission is in neutral, control is either returned to the operator or an engine synchronization system as described generally in this application is then actuated to synchronize the speed to that which will be necessary at the next expected gear. 
     Modern engine controls can achieve the above-described control parameters very quickly. All of the above calculations and speed modifications can be performed in a fraction of a second. Further, because of the simplified calculation and fewer variables utilized by the present invention, the data may be processed more quickly using less processor space. Known transition rate algorithms are used to achieve the desired values of engine speed. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, more variables may be added back into the simplified vehicle torque load equation of the present invention to achieve more accuracy. Also, certain vehicle parameters may be measured in real time instead of obtained from test data and visa versa. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.