Abstract:
An improved control method/system for controlling engine speed (ES) of an electronically controlled engine ( 12 ) communicating over an industry standard data link. If the difference between engine speed and target engine speed exceeds a reference value ((ES−ES TARGET )&gt;REF?), then the engine is commanded to operate in a torque control mode or a speed- and torque-limiting mode ( 64 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to automatic control of engine speed in a fully or partially automated vehicular transmission system including an electronically controlled engine, preferably communicating over an electronic data link and allowing control in at least a speed-limiting mode and in a torque-limiting mode. In particular, the present invention relates to control of engine speed for such systems when a relatively large decrease in engine speed is required, typically when synchronizing for an upshift. 
     2. Description of the Prior Art 
     Fully and partially automated mechanical transmission systems intended for medium- and heavy-duty vehicular use are well 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; 5,582,558; 5,735,771; 5,755,639; 5,797,110; 5,894,758 and 5,904,635, the disclosures of which are incorporated herein by reference. Such systems typically involve some automatic control of engine speed to synchronize for engaging a target gear ratio. 
     The current fully or partially automated transmission systems may include an electronically controlled engine having control logic conforming to and/or communicating over an electronic data link conforming to an industry standard protocol, such as SAE J-1922, SAE J-1939, ISO 11898 or the like. U.S. Pat. Nos. 5,457,633 and 5,738,606 are illustrative of such electronically controlled internal combustion (usually diesel) engines. 
     Such systems have an engine speed mode of operation wherein the engine is controlled to achieve a target engine speed. In heavy-duty diesel engines, the engines are programmed to respond to engine speed mode commands by fueling the engine to achieve the target engine speed in a smooth, ramped manner. 
     The prior art systems are subject to improvement, as when commanding a relatively large decrease in engine speed in the speed control mode of operation, usually during a single or skip upshift, a longer-than-desirable time may be required to achieve the target engine speed. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the drawbacks of the prior art are minimized or overcome by shortening the time required to achieve a relatively large decrease in engine speed to a target engine speed. 
     The foregoing is accomplished by operating in a torque control mode requesting a low torque, preferably zero torque, not in a speed control mode, when a significant decrease in engine speed is required. For the electronically controlled heavy-and medium-duty diesel engines produced by engine manufacturers, when in the torque control mode and when defueling to reduce torque, engine speed will decrease in an unmodulated manner according to the “decay rate” of the engine. 
     Accordingly, it is an object of the present invention to provide an improved engine speed control when substantial decreases in engine speed are required, such as in upshifts, which will decrease the time required to reach the desired engine speed. 
     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 a vehicular automated mechanical transmission system of the type with which the improved engine speed control of the present invention is particularly advantageously utilized. 
     FIG. 2 is a graphical representation of the rate of decrease in engine speed in a speed control mode versus a torque control mode of a typical heavy-duty diesel engine operating under an industry standard data link protocol such as SAE J-1922 or SAE J-1939. 
     FIG. 3 is a schematic illustration, in flow chart format, of the engine speed control of the present invention. 
     FIG. 4 is a schematic illustration, in flow chart format, of an alternate embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A typical vehicular powertrain  10  for a land vehicle, such as a heavy-duty or medium-duty truck, is schematically illustrated in FIG.  1 . The powertrain  10  includes a well-known diesel engine  12  and a multiple-speed, change-gear mechanical transmission  14  drivingly connected to the engine by means of a master friction clutch  16  and having an output shaft  18  connected to a final drive (such as a drive axle)  20 , by means of a prop shaft  22  and universal joints. The crankshaft  24  of the engine drives the input elements  26  of the master clutch  16 , which are frictionally engageable to and disengageable from output elements  28  carried by the transmission input shaft  30 . A manual  32  or automatic  34  control controls the engagement and disengagement of the master friction clutch  16 . Transmission  14  is preferably a 9-to-18-forward-speed transmission controlled by a manual shift lever  36  or an automatically controlled X-Y shifter  38  acting on a shift bar housing or shift shaft mechanism. 
     Transmission  14  is preferably a compound-type transmission of the range, splitter or combined range-and-splitter type, as may be seen in greater detail by reference to U.S. Pat. Nos. 4,754,665 and 5,390,561, the disclosures of which are incorporated herein by reference. Preferably, transmission  14  is of the mechanical type in which speed ratios are engaged and disengaged by means of engaging and disengaging one or more jaw clutches, which are preferably but not necessarily of the non-synchronized type. 
     A throttle pedal monitor assembly  40  monitors the position or displacement of the throttle pedal  42  and provides a signal (THL) indicative thereof. The engine includes a controller, preferably a microprocessor-based controller  44 , which communicates over an electronic data link and is effective to fuel the engine in accordance with commands over the data link. Typically, commands will request fueling to match operator throttle settings or to achieve a required engine speed and/or provide a maximum output (ie., flywheel) torque. 
     A microprocessor-based system controller  46  receives input signals  48  from the throttle pedal position sensor  40 , the transmission shift actuator  38 , signal GRT, from the driver command console  50 , signal ES indicative of engine speed from sensor  52 , signal IS from input shaft speed sensor  54 , and/or signal OS from output shaft speed sensor  56 . The input signals also may include a signal from the clutch actuator  34  indicative of the engaged or disengaged condition of master clutch  16  and/or the transmission operator  38 . X-Y shift mechanisms and shift position sensors may be seen by reference to U.S. Pat. Nos. 5,729,110 and 5,743,143. The system controller will process these input signals in accordance with predetermined logic rules to issue command output signals  58  to various system actuators, including the engine controller  44 . In certain systems, ECU  46  may be integral with the engine controller  44 . 
     As is well known, electronically controlled, heavy-duty diesel engines conforming to industry standard protocols such as SAE J-1922 and/or SAE J-1939 will receive and obey commands to operate in at least four different modes: 
     (1) a mode wherein engine fueling is under control of the vehicle operator and the engine will be fueled in accordance with the operator&#39;s positioning of the throttle pedal  42 ; 
     (2) an engine speed control mode wherein the engine will be fueled to achieve a commanded engine speed; 
     (3) a torque control mode wherein the engine will be fueled such that engine torque will achieve a requested maximum engine torque; and 
     (4) a speed- and torque-limiting mode wherein the engine is fueled such that engine speed and engine torque will not exceed requested maximum values thereof. 
     Torque usually is requested as a percentage of the maximum rated gross, output or other torque rating of the engine. 
     To complete a desired single or skip upshift by engaging non-synchronized jaw clutches, it is required that the engine speed be lowered to a substantially synchronous value (ES TARGET =(OX×GR T )±X). See, for example, U.S. Pat. No. 5,682,790, the disclosure of which is incorporated herein by reference. 
     In the prior art automated mechanical transmission systems, when it was necessary to significantly reduce engine speed to synchronize for engaging an upshift target gear ratio, the engine was commanded to operate in the engine speed control mode to achieve the target engine speed (ES=ES TARGET ). The engine then would implement the governor control required to reach this desired speed. The engine deceleration rate that occurs is dependent upon the engine manufacturer&#39;s implementation of the speed control mode and can sometimes be undesirably slow, as the implementation attempts to smoothly ramp to the target engine speed. “Ramped” is used to mean a modulated rate of deceleration less than the rate of unmodulated engine deceleration. Line  62  in FIG. 2 schematically illustrates a typical response in the engine speed control mode to decrease engine speed to the desired engine speed to engage the target gear ratio. 
     According to the present invention, Applicants have discovered that when a significant decrease in engine speed is required, by using the torque control mode or the speed- and torque-limiting mode and requesting that maximum torque to set to a relatively low value (such as zero torque), the engine will decelerate toward the desired engine speed as quickly as possible without any attempt by the engine controller to smoothly ramp the value. This will assure that the maximum engine deceleration rate is obtained and shorten the time to complete an upshift. Line  64  in FIG. 2 schematically illustrates engine speed in the torque control mode with a zero torque command. A similar line would be seen in the speed- and torque-limiting mode of operation. As the speeds of the engaging jaw clutch members pass through synchronous, the jaw clutch members will engage. This is especially true for engaging splitter clutches, which do require precision to engage. FIG. 3 is a schematic illustration, in flow chart format, of the upshift engine speed control method of the present invention. This is less desirable, as the system may cause engine speed to “chase” torsional vibrations in the driveline. 
     In another alternative mode, illustrated in FIG. 4, whenever current engine speed exceeds target engine speed (ES&gt;ES TARGET ), operation in the torque control mode or the speed- and torque-limiting mode may be commanded. 
     Alternatively, as engine speed approaches within a relatively narrow band (about ±10-20 RPM) of the target synchronous speed  66 , the engine then may be commanded to operate in the engine speed control mode and to achieve the exact target engine speed. 
     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 detailed are possible without departing from the spirit and scope of the invention as hereinafter claimed.