Abstract:
A control system/method to initiate upshifts in an automated mechanical transmission system ( 12 ). Upshifts are normally initiated on the basis of sensed throttle position (THL) or demand. In certain situation upshifts are initiated on the basis of sensed or calculated engine torque.

Description:
RELATED APPLICATIONS 
     This application is related to copending U.S. Ser. No. 09/145,316 filed Aug. 31, 1998 pending and assigned to EATON CORPORATION, assignee of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improved shift logic for an automated vehicular mechanical transmission system. In particular, the present invention relates to a control method/system having logic rules whereby in the automatic shifting mode, upshifts are initiated normally as a function of throttle position (demand) but, under certain conditions, are initiated as a function of engine torque and not of throttle position (demand). 
     2. Description of the Prior Art 
     Fully and partially automated vehicular mechanical transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4,850,236; 5,109,721; 5,393,276; 5,409,432 and 5,425,284, the disclosures of which are incorporated herein by reference. Such transmissions having an automatic shift mode typically base shift decisions upon shift point profiles or shift schedules, which often are graphically represented on a graph of throttle position (demand) versus engine, output shaft or vehicle speed. It is known to temporarily modify these shift profiles in view of various sensed vehicle operating conditions to modify vehicle performance, for antihunt purposes or the like. Examples of such shift logic may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802; 4,852,006; 4,916,979; 5,053,963 and 5,406,861, the disclosures of which are incorporated herein by reference. 
     While the prior art systems which based upshift decisions on demand usually responded to the driver&#39;s intent in most situations, a problem not addressed by the prior art shift logic involves systems which will cause engine torque to be significantly restricted, regardless of throttle position, under certain operating conditions. These systems include all-speed governors, road-speed governors (when maximum ground speed is being approached), gear-down protection, etc. When these systems are active to significantly restrict engine torque regardless of a relative high throttle position, basing upshift decisions on demand will delay upshifting, usually in opposition to the driver&#39;s intent. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a new and improved automated change-gear shift control, including improved upshift initiation control logic, is provided. 
     This is accomplished by providing logic rules whereby, under at least certain operating conditions, the normally utilized, demand-based upshift schedule is replaced by an engine torque-based upshift schedule. By way of example, if the actual torque being developed by the engine is less than of predetermined percentage (such as, for example, 25-50%) of the torque being requested by the throttle position, then upshift initiation decisions will be based on engine torque rather than on demand. 
     Accordingly, it is an object of the present invention to provide a new and improved automated change-gear transmission shift control system/method. 
     This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an at least partially automated vehicular mechanical transmission system utilizing the control logic of the present invention. 
     FIG. 2 is a schematic illustration, in graphical format, of a traditional shift schedule. 
     FIG. 3 is a schematic illustration, in flow chart format, of the upshift control logic of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a vehicle powertrain  10  including an at least partially automated mechanical transmission system  12  utilizing the upshift control logic of the present invention. Powertrain  10  includes an internal combustion engine  14  (such as a gasoline or diesel engine), a master clutch  16  having an input  16 A member and an output  16 B member, a mechanical transmission  18 , and a drive axle assembly  20  driven by propeller shaft  21 . While the present invention is particularly well suited for medium- and heavy-duty vehicles, it is not so limited. 
     Transmission  18  may be of a standard 5-, 6-, 7-, 9-, 10-, 12-, 18- or greater forward speed design. Examples of such transmissions may be seen by reference to U.S. Pats. No. 4,373,403; 4,754,665; and 5,390,561, the disclosures of which are incorporated herein by reference. 
     The automated transmission system  12  preferably will include microprocessor-based controller  22  for receiving various input signals  24  and processing same according to logic rules to issue command output signals  26  to various system actuators. Controllers of this type are known, as may be seen by reference to aforementioned U.S. Pat. Nos. 4,361,060 and 4,595,986. 
     A throttle position sensor  28  provides a signal THL indicative of operator-set throttle position or demand level, a shift selector  30  provides a signal GRS indicative of selected transmission operating mode and/or of a request for an up- or downshift for a currently engaged ratio, speed sensors  32 ,  34  and  36  provide signals ES, IS and OS, respectively, indicative of the rotational speed of the engine crank shaft  38 , the transmission input shaft  40  and the transmission output shaft  42 , respectively. Preferably, the sensors will sense, or the controller will calculate, a value d/d(THL) indicative of the rate of change with respect to time of throttle pedal position or driver&#39;s demand. 
     An engine controller  44  is provided for controlling speed or torque of the engine, a clutch actuator  46  may be provided for controlling operation of the master clutch, and a transmission operator  48  is provided to control shifting of the transmission. Alternatively, the clutch may be utilized only for starting and stopping the vehicle and may be controlled by a manual clutch pedal  49 . An upshift brake  41 , preferably under control of ECU  22 , also may be provided. 
     The ECU  22  may be separate or integral with the engine controller  44 . The various controllers, sensors and/or actuators may communicate over a data bus conforming to an industry standard protocol, such as SAE J-1939 or the like. 
     Suitable sensors and actuators are known to those of ordinary skill in the art and examples thereof, not intended to be limiting, may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,873,881; 4,974,468; 5,135,218; 5,279,172; 5,305,240; 5,323,669; 5,408,898; 5,441,137, 5,445,126; 5,448,483 and 5,481,170. 
     As is known, in automated transmission systems of this type, when operating in an automatic shifting mode (such as, for a non-limiting example, “D” on selector  30 ), upshifts and downshifts are commanded according to a “shift schedule” or “shift point profile,” a typical version of which is illustrated in FIG.  2 . Shift schedules, or the functional equivalents thereof, typically are stored in the memories of the controllers  22 . The present invention also is applicable to those transmission systems wherein only the upper ratios are automated. 
     FIG. 2 is a typical upshift shift point profile for a heavy-duty vehicle having a diesel engine governed to 2100 RPM and a 10-to- 12-forward-speed mechanical transmission. In the prior art, throttle position, also referred to as driver demand, is plotted on the horizontal axis against a speed (such as output shaft or, usually, engine rotational speed) on the vertical axis. Line  60  is the upshift point profile and divides the chart into two operating areas, area A where no upshift is required, and area B where upshifts are required. According to the upshift logic, crossing of line  60  from area A to area B will result in an upshift (single or multiple) being commanded. 
     In the prior art, the demand is expressed as a throttle pedal position in percentage of displacement from non-displaced to fully displace. The percentage also may be a related value calculated from the data link (DL), such as the “Driver Demand Engine Percent Torque” available on SAW J-1939 data links or the like. 
     The prior art used demand-based shift point algorithms, as such logic normally provides good correlation to driver (or cruise control) intentions. However, with certain types of engine controls, such as all-speed governors, road-speed governors and gear-down protection devices, the torque actually supplied by the engine may be considerably less than the torque demanded by the throttle position. In such cases, basing upshift decisions on throttle position (i.e., demand) will result in delayed upshifting which is likely to be contrary to the driver&#39;s intentions. 
     Accordingly, if the actual engine torque (a parameter such as gross engine torque or flywheel torque, see U.S. Pat. No. 5,582,069) to considerably less than the torque associated with the driver&#39;s demand, this is an indication that a system is actually ramping back torque independently of the throttle pedal position (THL). 
     According to the present invention, upon sensing that engine torque is substantially limited (for example, if actual engine torque/demanded torque is less than a reference value (REF equal to about 20-50%)), then upshift points will be based upon the actual engine torque. 
     For example, referring to FIG. 2, if the operator has full throttle displacement but the engine is being limited to 50% of its maximum torque at a given engine speed, using demand-based upshift logic will result in an upshift point at about 62, while using a torque-based upshift logic will result in an upshift point at about 64. 
     Switching to torque-modulated upshift logic also require that transmission input shaft speed (IS) be somewhat less (for example, at least 50 RPM less) than the rated engine speed (2100 RPM). 
     FIG. 3 is a flow chart representation of the shift logic modification of the present invention. 
     Accordingly, it may be seen that a new and improved control system/method for upshifting has been provided. 
     Although the present invention has been described with a certain degree of particularity, it is understood that the description of the preferred embodiment is by way of example only and that numerous changes to form and detail are possible without departing from the spirit and scope of the invention as hereinafter claimed.