Abstract:
A powertrain system ( 10 ) control for controlling engine ( 12 ) output torque as a function of engaged ratio of a transmission ( 14 ). Separate torque limits, A, B, C, D, respectively, are set for start ratios, intermediate ratios, direct ratio and overdrive ratios. The torque limits are set such that A&lt;B&lt;C&gt;D and B&lt;D.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control for a vehicular powertrain comprising a fuel-controlled engine and a multiple-ratio drivetrain, including a multiple-speed transmission and a single- or mulitple-speed drive axle assembly. In particular, the present invention relates to a powertrain control wherein the maximum output torque of the engine is limited as a function of engaged drivetrain ratio. 
     2. Description of the Prior Art 
     Vehicular drivetrains including multiple-speed transmissions, usually compound transmissions, or simple transmissions coupled with multiple-speed axles, having 7, 9, 10, 13, 16, 18 or more forward speed ratios, are well known in the prior art, especially for heavy-duty vehicles, as may be seen by reference to U.S. Pat. Nos. 5,370,013; 5,527,237 and 4,754,665, the disclosures of which are incorporated herein by reference. 
     Control systems and methods for calculating engine output torque (also called “flywheel torque”) are known in the prior art, as may be seen by reference to U.S. Pat. No. 5,509,867, the disclosure of which is incorporated herein by reference. 
     Automated and manual transmission systems wherein engine output torque is controlled and/or limited as a function of engaged gear ratio and/or vehicle speed are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,477,827; 5,797,110; 5,457,633; 4,889,014; 5,738,606; 5,679,096 and 5,876,302, the disclosures of which are incorporated herein by reference. As is known, modern vehicular powertrains usually include electronically controlled engines, which may be controlled as to engine speed and/or engine torque. By way of example, according to the SAE J-1939 data link protocol, commands may be issued to the engine for fueling of the engine in accordance with (a) driver&#39;s fuel demand, (b) a requested engine speed, (c) a requested engine torque and/or (d) a requested maximum engine torque and/or engine speed. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved control system/method for a vehicular powertrain is provided, which will tend to maximize vehicle performance while protecting the drivetrain from possible damage and/or undue wear caused by allowing excessive torque to be applied thereto under certain vehicle operating conditions. The foregoing is accomplished by limiting engine output torque to a first maximum value when the drivetrain is in a start ratio condition, by limiting engine output torque to a second maximum value when the drivetrain is in an intermediate ratio (the second maximum value being greater than the first maximum value), allowing engine torque to equal a third maximum value greater than the second maximum value when the transmission is in a direct drive or 1:1 ratio, and allowing engine torque to equal a fourth maximum value when the transmission is in an overdrive ratio condition (the fourth maximum value being less than the third maximum value but greater than the second maximum value). 
     Accordingly, it is an object of the present invention to provide a new and improved engine output torque control for a vehicular drivetrain system, preferably a vehicular powertrain system including a transmission having a direct drive ratio. 
    
    
     This and other objects and advantages of the present invention will become apparent from a reading of the 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 powertrain system including an automated mechanical transmission system. 
     FIGS. 2A and 2B are charts illustrating the drive ratios and allowable drivetrain input torques for a typical heavy-duty vehicle powertrain system including a drivetrain having, respectively, a 7-speed and an 18-speed overdrive transmission. 
     FIG. 3 is a flow chart representation of the control of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A vehicular powertrain system  10  of the type advantageously utilizing the control of the present invention may be seen by reference to FIG.  1 . For purposes of illustration, system  10  is an automated mechanical transmission system including a fuel-controlled internal combustion engine  12  (such as a well-known diesel engine or the like), a multiple-speed mechanical transmission  14 , and a non-positive coupling  16  for drivingly coupling the engine  12  to the transmission  14 . Typically, non-positive coupling  16  will be a torque converter or a friction master clutch. The transmission  14  further includes an output shaft  20  for driving the vehicle drive axles  22 . The drive axles may be of the single-speed or mulitple-speed type. 
     Transmission  14  may be of the known mechanical type utilizing positive jaw clutches to engage and disengage selected gears to shafts for changing the ratio of input shaft rotational speed (IS) to output shaft rotational speed (OS). Transmissions of this type may be seen by reference to U.S. Pat. Nos. 4,764,665; 5,385,056; 5,390,561 and 5,416,698. 
     System  10  may include a plurality of sensors for providing input signals  24  to a microprocessor-based control unit  26 , which will process the input signals according to logic rules to generate command output signals  28  to various system actuators. 
     Speed sensors  30 ,  32  and  34  may be provided to provide input signals to the controller indicative of engine speed (ES), transmission input shaft speed (IS), and transmission output shaft speed (OS), respectively. A sensor  36  may be provided to provide an input signal indicative of the operator setting of the throttle pedal. A driver control console  38  is provided to allow the operator to select a transmission mode and to provide an input signal, GR, indicative thereof to the controller  26 . 
     An engine controller  40 , preferably microprocessor-based, may be provided for controlling fueling of the engine and for providing information to a data link, DL, indicative of the operating parameters of the engine. Preferably, the data link will comply with a known protocol, such as SAE J-1939 or the like. An actuator  42  may be provided for operating the non-positive coupling  16 . A transmission actuator  44  may be provided for operating the transmission  14  and for providing signals indicative of the engaged gear ratio and/or other transmission operating parameters. Engaged ratio also may be calculated by comparing the rotational speeds of the input and output shafts. 
     As used in this application, and as commonly used in the vehicular industry, the term “powertrain” will refer to the engine  12 , coupling  16 , transmission  14  and drive axles  12 , while the term “drivetrain” will refer to the coupling  16 , the transmission  14  and the axles  22 . 
     Transmission  14  is illustrated as an  18 -forward-speed transmission having a direct drive (1:1.00) ratio and two overdrive ratios (see FIG.  2 B). As is well known, in the direct drive ratio, the shafts are directly coupled and torque is not applied to the gears; accordingly, a much higher torque may be applied to the transmission in direct drive without damaging or causing excessive wear to the gears. It also is known that the higher rotational speeds associated with overdrive (i.e., ratios wherein output shaft rotational speed exceeds input shaft rotational speed) allows a higher input torque to be applied to the transmission than in greater than 1:1.00 reduction ratios without risking damage and/or undue wear. 
     According to the present invention, engine torque is limited to one of four maximum values according to the sensed or expected engaged ratio. FIG. 2A illustrates the application of the present invention to a 7-speed overdrive transmission. 
     In the start ratios, usually 1st through 6th in an 18-speed transmission, engine output torque is limited to a first maximum value (A). In the intermediate ratios, usually 7th through 15th in an 18-speed transmission, engine output torque is limited to a second maximum value (B). In direct, engine output torque is limited to a third maximum value (C). Value C may equal the maximum output of the engine. In overdrive ratios, 17th and 18th in the illustrated transmission, engine torque is limited to a fourth maximum value (D). 
     The maximum torque values are related as follows: 
     A&lt;B&lt;C&gt;D and 
     B&lt;D 
     Typical values of the maximum torque references are seen in FIGS. 2A and 2B, which are provided by way of example. In FIG. 2B, values for an RTLO 18918B transmission (available from Eaton Corporation, assignee of this application) and a typical heavy-duty vehicle diesel engine are provided. 
     FIG. 3 is a flow chart representation of the control of the present invention. 
     Torque values A, B, C and/or D may be ranges of values and/or may be subdivided. 
     Although the present invention has been described with a certain degree of particularity, it is understood that various modifications are possible without departing from the spirit and scope of the invention as hereinafter claimed.