Abstract:
A control system/method to minimize unwanted upshifts in an automated mechanical transmission system (12). Upshifts are prohibited unless throttle position (THL) has achieved a substantially steady-state value (|(d/dt(THL))|&lt;REF-1) or a speed value (ES, IS, OS) exceeds a reference (OS&lt;REF-2).

Description:
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 at least certain upshifts are commanded only at substantially steady-state throttle conditions to minimize the occurrence of unwanted upshifts. 
     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. 
     A problem not addressed by the prior art shift logic involves unwanted upshifting which occasionally occurred if the vehicle operator is rapidly changing throttle demand position. 
     Present demand-based shift point algorithms use instantaneous demand to determine the shift point speeds. In cases of steady-state or slowly varying demand, this provides logical shifting responses to the driver&#39;s demands, the shift point is pushed higher for heavy demand and lower for light demand. However, in the case of demand which is changing relatively quickly, this strategy can create shifts which do not follow with what the driver is trying to do. 
     If the driver is on the throttle but below the upshift point associated with his particular demand and then comes off the throttle, an upshift can be triggered with the present shift strategy as the demand transitions toward 0%. In this case, the driver may have intended to slow down, but the system upshifted. In another case, if the driver is off the throttle and then gets on it, an upshift can be triggered as demand increases. The driver may have wanted more power, but again, the system upshifted. In both cases, responding to a transitory demand level caused the system to upshift when the situation might have been better handled by remaining in place. 
     As a note, for setting downshift points, the prior art shift point strategy works logically based upon instantaneous demand. Increasing throttle is more likely to produce a downshift to provide more power, and decreasing throttle is more likely to hold the present gear for better fuel economy. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a new and improved automated change-gear shift control, including improved upshift control logic, is provided. 
     This is accomplished by providing logic rules whereby, under at least certain operating conditions and/or operator actions, the normally utilized upshift schedule is modified to prevent unwanted upshifts. By way of example, at relatively low transmission output shaft or engine speeds, upshifts are not commanded until operator-set throttle pedal position becomes relatively steady. 
     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 illustrating the drawbacks of the prior art. 
     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, 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- or greater forward speed design. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 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 a 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/dt(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 is provided for controlling operation of the master clutch, and a transmission operator 48 is provided to control shifting of the transmission. 
     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, &#34;D&#34; on selector 30), upshifts and downshifts are commanded according to a &#34;shift schedule&#34; or &#34;shift point profile,&#34; a prior art 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 top-gear upshift shift point profile for a heavy-duty vehicle having a diesel engine and a 10-to-12-forward-speed mechanical transmission. Throttle position, also referred to as driver demand, is plotted against a speed (such as output shaft or engine rotational speed). 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 prior art upshift shift logic, an instantaneous crossing of line 60 from area A to area B would immediately result in an upshift being commanded. 
     The prior art demand-based shift point algorithms use instantaneous demand to determine the shift point speeds. In cases of steady-state or slowly varying demand, this provides logical shifting responses to the driver&#39;s demands, the shift point is pushed higher for heavy demand and lower for light demand. However, in the case of demand which is changing relatively quickly, this strategy can create shifts which do not follow with what the driver is trying to do. 
     If the driver is on the throttle but below the upshift point associated with his particular demand (point 62) and then comes off the throttle, an upshift can be triggered (point 64) with the present shift strategy as the demand transitions toward 0% (point 66). In this case, the driver may have intended to slow down, but the system upshifted. In another case, if the driver is off the throttle (point 68) and then gets on it, an upshift can be triggered as demand increases (point 70). The driver may have wanted more power (point 72), but again, the system upshifted. In both cases, responding to a transitory demand level caused the system to upshift when the situation might have been better handled by remaining in place, i.e., not upshifting. 
     To minimize such overshifting, the shift logic of the present invention prohibits commanded upshifts until the operator has positioned the throttle pedal in a relatively stable, steady-state condition. This is sensed by the throttle pedal position remaining in an relatively small band of values (within a 5% band, by way of example) and/or the rate of change of throttle position with respect to time being lower than a reference value (|(d/dt(THL))|&lt;REF-1). If these conditions are met, upshifts may be commanded in accordance with the position of the current operating condition relative to the shift point profile of FIG. 2. 
     As may be seen, if speed is in excess of a certain value (REF-2), such as represented by line 74, the logic of the present invention is not necessary, as continued increasing or decreasing of demand will not cause a crossing and recrossing of shift point profile line 60. 
     As a note, for setting downshift points, the prior art shift point strategy works logically based upon instantaneous demand. Increasing throttle is more likely to produce a downshift to provide more power, and decreasing throttle is more likely to hold the present gear for better fuel economy. 
     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.