Abstract:
A system for controlling the engagement and disengagement of one or more clutches that are adapted to operatively connect an engine and an automatic transmission. The system including a control device for determining if a negative torque condition exists and to provide an output or signal to decrease the rotational speed of said engine in response to the determination of the existence of a negative torque condition.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally relates to an automatic transmission system and in particular to an automatic transmission system capable of providing improved fuel economy in connection with a negative torque condition.  
       BACKGROUND  
       [0002]     A factor that effects a vehicle&#39;s fuel efficiency is the load experienced by the engine. If the engine experiences a high load, or runs at high revolutions per minute, fuel efficiency typically is reduced. On the other hand, if the engine is unloaded, or runs at a relatively lower number of revolutions per minute, the fuel efficiency commonly improves.  
         [0003]     The load experienced by the engine may be directly related to the associated gear ratio in which the transmission is operating. Too high a numerical gear ratio may cause the engine to run too fast and fail to operate at a desired level of fuel efficiency. Conversely, an extremely low numerical gear ratio may adversely affect vehicle performance characteristics, including acceleration and ease of operation. Accordingly, communication between the engine and the transmission in determining the load experienced by the engine and determining a desired or proper gear ratio can improve fuel efficiency.  
       SUMMARY  
       [0004]     A system for controlling the engagement and disengagement of one or more clutches that are adapted to operatively connect an engine and an automatic transmission. The system including a control system for determining if a negative torque condition exists and to provide an output or signal to decrease the rotational speed of said engine in response to the determination of the existence of a negative torque condition.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a functional block diagram of a vehicle powertrain system, including an automatic transmission, according to an embodiment of the invention.  
         [0006]      FIG. 2  is a graph of an engine speed curve that generally illustrates a speed curve when the engine is in a loaded condition and a neutral condition.  
         [0007]      FIG. 3  is a gear selection graph according to an embodiment of the invention in which gear selection ranges are associated with throttle position and vehicle speed.  
         [0008]      FIG. 4  is a functional flow chart of a powertrain response according to an embodiment of the invention.  
         [0009]      FIG. 5  is a graph generally illustrating a disengagement and pre-engagement of a clutch during a negative torque condition. 
     
    
     DETAILED DESCRIPTION  
       [0010]     Referring to  FIG. 1 , a schematic illustration of an exemplary powertrain system  5  is shown. The powertrain system  5  includes an engine  10  having an output shaft  12  and an automatic transmission  14  having an input shaft  16  and an output shaft  18 . Positioned between engine output shaft  12  and transmission input shaft  16  is a torque converter  20 . Torque converter  20  may further include an impellor, a turbine and a stator. The output shaft  18  is commonly in communication with a differential assembly  22 , which in turn provides torque to a plurality of wheels  24 .  
         [0011]     The automatic transmission  14  may be a continuously variable transmission, such as a belt driven transmission, or may a fixed ratio transmission, such as a planetary transmission, or may be a step-change transmission, with an automated clutch and automated gear changes. Thus, it can be appreciated that the invention is not limited by the design, or type, of automatic transmission. The automatic transmission  14  may include a plurality of clutches that are capable of being engaged and disengaged, or vented, to connect and/or disconnect the output shaft  12  of the engine  10  with the input shaft  16  of the automatic transmission  14 , respectively.  
         [0012]     The engine  10  may be in communication with an engine controller  28  and the transmission  14  may be in communication with a transmission controller  30 , either or both which may be integrated into or be provided in communication with a control module or control device  32 , such as a computer module, a powertrain control module (PCM), or the like. While the invention is described below as having an engine controller  28  and a transmission controller  30  that together form or function as part of a control device, it can be appreciated that the invention may be practiced with engine  10  and the transmission  14  in direct communication with a control device  32  that functions as or includes (or integrates) an engine controller and/or a transmission controller, thereby eliminating the need for a separate engine controller  28  and/or a separate transmission controller  30 .  
         [0013]     In the illustrated embodiment, the control device  32  receives powertrain operating conditions from various sensors and can communicate outputs control signals to the engine  10  and the transmission  14 . The sensors providing input to the control device (shown in the illustrated embodiment in the form of a PCM) may include, without limitation, an engine speed sensor (not shown), a turbine output shaft sensor (not shown), an accelerator pedal input sensor  34 , and/or a vehicle speed sensor (not shown). An engine speed sensor may detect, for example, revolutions of an engine output shaft  12  and may provide or generate a signal indicative of the detected engine revolutions per minute (Ne). A turbine output shaft sensor may detect, for example, revolutions of a turbine output shaft and provide or generate a signal indicative of the detected revolutions per minute (Nt). An accelerator pedal input sensor (e.g., sensor  34 ) may detect, for example, the degree of depression or position of an accelerator pedal and provide or generate a signal indicative of the detected accelerator pedal position. Further, a vehicle speed sensor may detect, for example, the speed at which the vehicle is currently traveling and provide or generate a signal indicative of a detected speed.  
         [0014]     The control device  32  or the engine controller  28  may further include an electronic throttle control  36 . The throttle control  36  is capable of detecting, for example, the position or degree of opening of an engine throttle or throttle pedal position and providing or generating a signal indicative of detected throttle opening and/or throttle position.  
         [0015]     The control device  32  or the transmission controller  30  may regulate, or control, the engagement and disengagement of one or more clutches  26  (which are only generically identified in connection with  FIG. 1 ) based upon input or signals received from an electronic throttle control  36  and a vehicle speed sensor. It is to be understood that the invention is not limited to a specific clutch configuration, including that generally set forth in connection with  FIG. 1 .  
         [0016]     Referring to  FIG. 3 , the selection, or determination, of a desired or appropriate gear for the transmission  14  may be determined based upon signals or information provided concerning throttle opening/position and vehicle speed. In turn, the gear selection will, at least in part, determine which combination of clutches  26  should be engaged or disengaged with respect to the transmission  14 . Four gears are represented in  FIG. 3 . However, it can be appreciated that the system is not limited to three gears and may be practiced by including more or less gears.  
         [0017]     The engine controller  28  and the transmission controller  30  may be configured for direct communication between each other. For instance, if the transmission  14  is in neutral, i.e., the clutches  26  are disengaged or vented, the transmission controller  30  may provide a signal to the engine controller  28  signaling that the transmission  14  is not loaded, or that a lower torque requirement may be present or occurring. In turn, the engine controller  28  may provide a signal to the engine  10  to reduce engine speed, or run at a lower number of revolutions per minute (rpm), which can result in fuel savings.  
         [0018]     In contrast, if the transmission  14  is in gear, i.e. the clutches  26  are engaged, the transmission controller  30  may provide a signal to the engine controller  28  signaling that the transmission  14  is loaded, or that an increased torque requirement may be present or occurring. In turn, the engine controller  28  may provide a signal to the engine  10  to increase or ramp up the engine speed or rpm.  FIG. 2  illustrates a general example of an engine speed curve in accordance with an embodiment of the invention. The illustrated graph depicts an engine speed curve through a period of time in which the engine  10  is loaded, i.e., running at X rpm, and when the engine  10  is unloaded, or in a neutral condition.  
         [0019]     In certain situations, the powertrain system  5  may experience a negative torque condition. A negative torque condition may occur, for example, when the engine  10  is not producing an overall positive torque within the powertrain system  5 , when the turbine is revolving at a higher rate than the impeller within the torque converter  20 , or when the turbine is revolving at a higher rate than the engine  10 , i.e. when the transmission  14  is attempting to drive the engine  10 . By way of example, and without limitation, a negative torque condition may be present when the following conditions exist: 
        (1) the engine&#39;s revolutions per minute is less than the turbine&#39;s revolutions per minute plus a constant (Ne&lt;Nt+a constant); and     (2) the electronic throttle control sensor senses a throttle opening less than a given number of degrees (e.g., 2 degrees (thr&lt;2°)); and     (3) the above conditions are present for a select or predetermined time, for example, 1.3 seconds. 
 
 Such a situation may occur, for instance, when the operator of a vehicle requests a deceleration of the vehicle by engaging the brakes, or by initiating a neutral coast down situation by removing or reducing pressure on the accelerator pedal. When such a situation occurs, the engine  10  may be running at a higher rpm than necessary based upon the torque output of the transmission. Accordingly, the engine&#39;s rpm may be reduced to help improve associated fuel efficiency. 
       
 
         [0023]     Referring now to  FIGS. 4 and 5 , a flowchart illustrates a response by the powertrain system  5  to a negative torque condition which, among other things, may improve the fuel efficiency of the powertrain system  5 . In the illustrated embodiment of the response, a control device  32  (or its functional equivalent) determines if a negative torque condition is or may be occurring based upon signals provided by or received from an engine controller  28  and a transmission controller  30  (step S 1 ). If it is determined that a negative torque condition is not present or occurring, the powertrain system  5  may continue as it is currently operating, the clutches  26  engaged to the transmission  14  remain engaged (step S 2 ) and the system returns or loops back to the initial inquiry (step S 1 ).  
         [0024]     Conversely, if the control device  32  (or its functional equivalent) determines that a negative torque condition is present, then the control device  32  provides a signal to the transmission controller  30  to initiate the release, or venting, of the engaged clutches  26  (step S 3 ). Once the transmission controller  30  receives the signal from the control device  32 , all clutches  26  engaged to the transmission  14  can be vented, or disengaged (step S 4 ). When all clutches  26  are vented, the transmission  14  is in neutral gear condition.  
         [0025]     The control device  32  then may continue to analyze current vehicle operating conditions, including vehicle speed and throttle position, to determine which clutches  26  should or would be desirably engaged once the negative torque condition is canceled or no longer exists. Once the control device  32  has determined which clutch combination is appropriate, a select or predetermined amount of pressure may be provided to at least one of the clutches  26  in preparation for the engagement of the appropriate clutch configuration once the negative torque condition has passed or no longer exists (step S 5 ). For instance, the select or predetermined amount of pressure may be slightly less than the pressure necessary to keep the clutch(es) from slipping, or may be a percentage of the total pressure applied to the clutch(es) during engagement.  
         [0026]     Referring to  FIG. 5 , a graph is presented that generally illustrates the pressure applied or removed from the clutches during steps S 4  and S 5 . As illustrated, during step S 4 , pressure is removed from the engaged clutches such that the clutches may slip, or become disengaged. Once that occurs, during step S 5 , pressure is applied to at least one clutch so that once the negative torque condition is abated or removed and only a minimal amount of pressure may be necessary to engage the clutch. Applying the select or predetermined amount of pressure to one of the clutches  26  typically reduces the amount of time necessary for clutches  26  to engage the transmission  14  once the negative torque condition is no longer present. As a result, the transmission  14  may transition more smoothly from neutral to a loaded or in-gear condition.  
         [0027]     Once the negative torque condition is canceled or no longer exists, the appropriate clutches  26  may be engaged to the transmission  14  and a signal may be provided by the transmission controller  30  to the engine controller  28  to increase engine speed accordingly. For instance, the negative torque condition may be canceled by a driver when an accelerator pedal is depressed to increase the vehicle&#39;s acceleration. In another example, the negative torque condition may be canceled automatically if the control device  32  senses that vehicle speed is increasing despite the prior application of brakes. In a further example, if the control device  32  senses that vehicle acceleration is changing beyond a select or predetermined rate, the clutches may be automatically engaged to the transmission for safety purposes. Either of the foregoing situations could be present if the vehicle is heading down a hill or slope.  
         [0028]     The present invention has been particularly shown and described with reference to the foregoing embodiments, which are merely illustrative of the best modes for carrying out the invention. It should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.