Patent Publication Number: US-7909732-B2

Title: Selectable drivetrain control for a vehicle

Description:
This application is a divisional of co-pending U.S. patent application Ser. No. 11/686,062, filed Mar. 14, 2007, the entire contents of which are hereby incorporated herein by reference thereto. 
    
    
     FIELD 
     The present invention relates generally to a selectable drivetrain control for a vehicle, in particular to a control to selectably set a transmission gear position, limit the displacement of a throttle and limit ignition timing while the vehicle&#39;s brake and accelerator pedals are simultaneously actuated. 
     BACKGROUND 
     A motor vehicle driver typically controls the speed of a conventional vehicle using foot pedals, which in a vehicle with an automatic transmission are the accelerator pedal and the brake pedal. Drivers will normally use the same foot to control both the accelerator pedal and the brake pedal. However, some drivers of automatic transmission vehicles use two feet, one to actuate the accelerator pedal and the other to actuate the brake pedal. This can result in simultaneous activation of both the vehicle brake and throttle. In certain situations a stall condition may occur due to simultaneous activation of both the brake and the throttle, subjecting the vehicle&#39;s drivetrain to significant stress. 
     Others have attempted to limit drivetrain stress due to simultaneous actuation of the vehicle&#39;s brake and accelerator pedals by reducing or limiting the throttle setting under such conditions, thereby limiting the amount of torque generated by the vehicle&#39;s engine and delivered to a transmission system. An example may be found in U.S. Pat. No. 6,125,315, issued to Kon, the contents of which are hereby incorporated herein by reference. The system disclosed by Kon limits the degree of opening of the throttle when a stall condition is detected, thereby reducing stress imposed on the vehicle&#39;s drivetrain. However, such systems do not address the unique stresses imposed upon a four-wheel drivetrain when a vehicle is operated such that the brake and accelerator pedals are actuated under road conditions wherein some, but not all, of the wheels lose traction. 
     For example, many vehicles are now equipped with an “on-demand” four-wheel drive transmission system wherein a varying amount of torque is provided to each axle in order to maintain traction under varying road conditions. One of the most severe of these road conditions occurs when the wheels of one axle of the vehicle lose traction due to, for example, ice or snow while the wheels of the other axle retain traction. When launching the vehicle from a stalled state under these conditions a large amount of torque is transferred to the axle having traction due to the lack of traction in the other axle, thereby imposing significant stress upon the drivetrain. However, if a vehicle under the same conditions is equipped with a vehicle stability control system the amount of torque transferred to the axle having traction may be reduced because the vehicle stability system limits and compensates for a loss of traction in the other axle by reducing engine power and applying brake intervention to reduce wheel slip on low traction surfaces. This reduction of wheel slip reduces the amount of torque transferred to the axle having traction, thereby reducing stress on the drivetrain. 
     It would be desirable to utilize a vehicle&#39;s traction control system in conjunction with a throttle limiting system in order to tailor the operating performance of the vehicle under stall launch conditions wherein the brake and throttle are activated simultaneously. Such a system would be particularly useful for increasing the operating performance of an on-demand four-wheel drive transmission under varying road conditions while still protecting the drivetrain from damage. 
     SUMMARY 
     The present invention utilizes the engagement status of a vehicle stability/traction control system to establish the operational parameters of the vehicle&#39;s drivetrain when the brake and accelerator pedals are simultaneously actuated. In a first “performance” configuration, when the vehicle stability/traction control is engaged by the driver and the brake and accelerator are simultaneously actuated, the vehicle&#39;s transmission is automatically placed into first gear and the vehicle&#39;s throttle is automatically set to a predetermined reduced setting. Conversely, in a second “preservation” configuration, when the vehicle stability/traction control is disengaged by the driver and the brake and accelerator pedals are simultaneously actuated, the transmission is placed into second gear while the throttle is set to a predetermined reduced setting that is lower than that of the “performance” configuration. 
     One aspect of the present invention is a selectable drivetrain control for a vehicle. The drivetrain control includes a controller configured to receive input signals and issue predetermined output command signals corresponding to the status of the input signals. A first sensor is configured to provide an input signal to the controller relating to the actuation status of a brake pedal. A second sensor is configured to provide an input signal to the controller relating to the actuation status of an accelerator pedal. A stability control selector is configured to provide an input signal to the controller relating to the engagement status of a stability control system of the vehicle. A drivetrain is configured to receive output command signals from the controller. The controller issues output command signals to the drivetrain to control the operational characteristics of the drivetrain, responsive to the engagement status of the stability control system while the brake and accelerator pedals are simultaneously actuated. 
     Another aspect of the present invention is a method for controlling the operational characteristics of a drivetrain of a vehicle. The method includes the steps of monitoring the actuation status of a brake pedal, an accelerator pedal and a stability control system of the vehicle. While both the brake pedal and accelerator pedal are simultaneously actuated and the stability control system is not engaged, a throttle of an engine of the drivetrain is set to a first predetermined position. An engine ignition timing advance is set to a position corresponding to the first throttle position. A first gear setting of a transmission of the drivetrain is also selected. While both the brake pedal and accelerator pedal are simultaneously actuated and the stability control system is engaged, the throttle is set to a second predetermined position. Furthermore, the ignition timing advance is set to a position corresponding to the second throttle position. Lastly, a second transmission gear setting is selected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the inventive embodiments will become apparent to those skilled in the art to which the embodiments relate from reading the specification and claims with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram showing the general arrangement of a relevant portion of a vehicle drivetrain control system according to an embodiment of the present invention; 
         FIG. 2  is a flow diagram showing operational steps associated with the system of  FIG. 1 ; 
         FIG. 3A  is a graph of throttle response versus depression of an accelerator pedal with respect to time for a first condition of the system of  FIG. 1 ; 
         FIG. 3B  is a graph of engine ignition timing advance with respect to time for a first condition of the system of  FIG. 1 ; 
         FIG. 3C  is a graph of brake pedal actuation state with respect to time for a first condition of the system of  FIG. 1 ; 
         FIG. 3D  is a graph of transmission gear setting with respect to time for a first condition of the system of  FIG. 1 ; 
         FIG. 4A  is a graph of throttle response versus depression of an accelerator pedal with respect to time for a second condition of the system of  FIG. 1 ; 
         FIG. 4B  is a graph of engine ignition timing advance with respect to time for a second condition of the system of  FIG. 1 ; 
         FIG. 4C  is a graph of brake pedal actuation state with respect to time for a second condition of the system of  FIG. 1 ; and 
         FIG. 4D  is a graph of transmission gear setting with respect to time for a second condition of the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A schematic block diagram showing the general arrangement of a relevant portion of a drivetrain control system  10  for a vehicle according to an embodiment of the present invention is shown in  FIG. 1 . System  10  comprises a controller  12  configured to control the operation of a drivetrain  14  coupled thereto. Drivetrain  14  includes in pertinent part a transmission gear selector  16  that is coupled to an automatic transmission  18 . Drivetrain  14  further includes a throttle position actuator  20  and an ignition timing control  22 , each coupled to an engine  24 . 
     Controller  12  receives status signals from any or all of a brake pedal state sensor  26 , an accelerator pedal state sensor  28 , and a stability control selector  30 , and controls the operation of system  10  in a predetermined manner. Example control tasks for controller  12  may include, without limitation, providing predetermined output command signals to any or all of transmission gear selector  16 , throttle position actuator  20  and ignition timing control  22 , the command signals corresponding to the condition of the status signals. Controller  12  may also detect fault conditions with the components of system  10  and/or interconnections thereof. Non-limiting example fault conditions may include internal faults within controller  12 , open or shorted electrical connections, low input power supply voltage to system  10 , and predetermined fault conditions present in any or all of transmission gear selector  16 , throttle position actuator  20  ignition timing control  22 , brake pedal state sensor  26 , accelerator pedal state sensor  28  and stability control selector  30 . Controller  12  may be configured using conventional analog or digital electronic circuitry or a combination thereof, and may utilize conventional memory devices such as magnetic, electronic and optical memory storage devices containing a predetermined set of instructions, such as a computer program. 
     Transmission gear selector  16  may be any type of device suitable for receiving an electrical gear selection command signal from controller  12  and selecting a corresponding gear setting of automatic transmission  18 . Example devices include, without limitation, actuators, clutches, solenoids, relays and electro-hydraulic cylinders. Transmission gear selectors are well-known in the art and thus will not be detailed further herein. 
     Transmission  18  may be any conventional type of automatic transmission configured to transmit power from engine  24  to a set of drive wheels (not shown) including, without limitation, a front-wheel drive transmission, rear-wheel drive transmission, a selectable four-wheel drive transmission, an all-wheel drive transmission and an on-demand four-wheel drive transmission. Such transmissions are well-known in the art and thus will not be detailed further herein. 
     Throttle position actuator  20  may be any conventional type of device suitable for receiving an electrical throttle command signal from controller  12  and setting an air/fuel mixture of a fuel supply for engine  24  to a predetermined flow quantity and mixture ratio corresponding in a predetermined manner to the electrical throttle command, resulting in a predetermined engine speed. Example throttle position controls include, without limitation, electro-mechanical actuators, electro-hydraulic cylinders, and relays. Throttle position actuators are well-known in the art and thus will not be detailed further herein. 
     Ignition timing control  22  may be any conventional type of device suitable for receiving an electrical timing control signal from controller  12  and setting the timing of the ignition system of engine  24  to a predetermined advance corresponding to the throttle position of the engine. Example ignition timing controls include actuators, relays and valves suitable for controlling any or all of a mechanical, vacuum, or electronic ignition control of engine  24 . Ignition timing and advance controls are well-known in the art and thus will not be detailed further herein. 
     Engine  24  may be any type of engine now known or later developed that generates motive power for a vehicle. Examples include, without limitation, internal combustion (IC) engines, hybrid electric-IC engines and electric motors. 
     Brake pedal state sensor  26  provides a status signal to controller  12  as to whether or not a brake pedal  32  of the vehicle is being actuated by the driver. Brake pedal state sensor  26  may be any type of conventional mechanical or electrical encoder, transducer or switch. Brake pedal state sensor  26  may be powered by controller  12 , or may be separately powered. The status signal provided to controller  12  by brake pedal state sensor  26  may be any form of digital or analog electrical signal compatible with the controller. 
     Accelerator pedal state sensor  28  provides a status signal to controller  12  as to whether or not an accelerator pedal  34  of the vehicle is being actuated by the driver. Accelerator pedal state sensor  28  may be any type of conventional mechanical or electrical encoder, transducer or switch. Accelerator pedal state sensor  28  may be powered by controller  12 , or may be separately powered. The status signal provided to controller  12  by accelerator pedal state sensor  28  may be any form of digital or analog electrical signal compatible with the controller. 
     Stability control selector  30  is a control, such as a switch actuable by the driver of the vehicle to enable or disable a stability control system of the vehicle. Stability control selector  30  is typically located within convenient reach of the driver, on the dashboard or the gear selector lever. Alternatively, stability control selector  30  may be a conventional sensing device configured to monitor the stability control system and provide to controller  12  a status signal indicating whether or not the stability control system is engaged. The stability control system, when engaged by actuation of stability control selector  30 , automatically detects when the vehicle has deviated from the driver&#39;s steered direction and compensates for oversteering, understeering and instability by selectively braking individual wheels and/or reducing engine torque to bring the vehicle back on course. Such systems are well-known in the art and are commonly termed as “dynamic stability control,” “stability control program” and “electronic stability control,” among others. 
     With reference now to  FIGS. 1 ,  2  and  3 A- 3 D in combination, the operation of system  10  will now be described. The operation of system  10  begins at step s 100 , controller  12  first checking brake pedal state sensor  26  at step s 102  to determine whether brake pedal  32  is being depressed (i.e., actuated) by the driver of the vehicle. If brake pedal  32  is depressed ( FIG. 3C ), controller  12  checks accelerator pedal state sensor  28  at step s 104  to determine whether accelerator pedal  34  is also being depressed (i.e., actuated) by the driver. If accelerator pedal  34  is also being depressed ( FIG. 3A ), controller  12  checks stability control selector  30  at step s 106  to determine whether the stability control system is engaged. 
     If stability control selector  30  indicates that the stability control system is not engaged, as at s 108 , drivetrain protection steps s 110 , s 112  and s 114  are executed. Controller  12  issues output commands to throttle position actuator  20  at step s 110  to set the actuator  20  (and, accordingly, engine  24 ) to a predetermined minimum throttle condition ( FIG. 3A ). Controller  12  also issues commands to ignition timing control  22  to set the ignition advance to a predetermined minimum advance setting corresponding to the predetermined minimum setting of throttle position actuator  20 . Controller  12  likewise issues commands to transmission gear selector  16  to place transmission  18  into a predetermined intermediate gear setting, such as second gear ( FIG. 3D ). In this configuration, even if the driver fully depresses accelerator pedal  34  while actuating brake pedal  32  as indicated by  FIGS. 3A and 3C , the amount of torque developed by engine  24  is at a predetermined minimal value as indicated by the throttle position ( FIG. 3A ) and ignition timing advance ( FIG. 3B ). These conditions continue while brake pedal  32  and accelerator pedal  34  are simultaneously depressed, thereby protecting transmission  18  and engine  24  from high stress levels that could result in excess wear or damage thereto. 
     When brake pedal  34  is released at a subsequent time “T1” ( FIG. 3C ), controller  12  responds at step s 115  by issuing commands to transmission gear selector  16  to place transmission  16  into first gear ( FIG. 3D ). Furthermore, controller  12  issues normal-operation restoration commands to throttle position actuator  20  and ignition timing control  22  to allow for a ramp-up of engine  24  throttle ( FIG. 3A ) and ignition timing advance ( FIG. 3B ), providing for a gradual increase in drivetrain  14  output to amount that corresponds in a predetermined manner to the position of accelerator pedal  34 . Normal throttle, ignition timing and transmission gear selection of drivetrain  14  are then maintained and steps s 100 , s 102 , s 104  and s 115  are repeated while brake pedal  32  and accelerator pedal  34  are not simultaneously actuated. 
     If both the brake and accelerator pedals  32 ,  34  are actuated at steps s 102 , s 104  and if stability control selector  30  indicates that the stability control system is engaged, as at s 116 , drivetrain performance limiting steps s 118 , s 120  and s 122  are executed as illustrated by reference to FIGS.  1  and  4 A- 4 D. Controller  12  issues commands to throttle position actuator  20  at step s 118  to set actuator  20  (and, accordingly, engine  24 ) to a predetermined maximum throttle condition corresponding to the position of accelerator pedal  34 . ( FIG. 4A ). Controller  12  also issues commands to ignition timing control  22  to set the ignition advance to a predetermined maximum-limit advance setting corresponding to a predetermined maximum setting of throttle position actuator  20 . Controller  12  likewise issues commands to transmission gear selector  16  to place transmission  18  into a predetermined low gear setting, such as first gear ( FIG. 4D ). In this configuration the throttle position and ignition timing of engine  24  are limited by system  10  to the predetermined maximum-limit value, thereby providing drivetrain  14  with a greater amount of torque for greater vehicle performance than is available when stability control selector  30  is OFF. This may be desirable under certain adverse conditions, such as freeing the vehicle when mired in snow or mud. 
     When brake pedal  34  is released (i.e., de-actuated) at a subsequent time “T2” ( FIG. 4C ), controller  12  responds at step s 115  by issuing normal-operation restoration commands to throttle position actuator  20  and ignition timing control  22  to allow for an increase in engine  24  throttle ( FIG. 4A ) and ignition timing advance ( FIG. 4B ), providing for an increase in drivetrain  14  output from the maximum-limit setting to an amount that corresponds in a predetermined manner to the position of accelerator pedal  34 . Normal throttle, ignition timing and transmission gear selection of drivetrain  14  are then maintained and steps s 100 , s 102 , s 104  and s 115  are repeated while brake pedal  32  and accelerator pedal  34  are not simultaneously actuated. 
     It should be noted that the predetermined maximum-limit throttle and ignition advance settings for the conditions of steps s 118 , s 120 , s 122  shown in  FIGS. 4A and 4B  are not necessarily equal to the maximum settings that can be obtained when brake pedal  32  and accelerator pedal  34  are not simultaneously depressed. For example, in some embodiments of the present invention the predetermined maximum-limit throttle setting and maximum-limit ignition advance timing may be significantly less than the maximum settings available for engine  24  under normal vehicle operating conditions wherein brake pedal  32  and accelerator pedal  34  are not simultaneously actuated. The predetermined maximum-limits for the throttle setting and ignition advance timing are preferably established such that a greater amount of power is transmitted to the drive wheels of the vehicle than the drivetrain protection mode steps s 110 , s 112 , s 114  while still providing a measure of protection against damage or excessive wearing of drivetrain  14 . 
     The process of  FIG. 2  ends at s 124 . The process may be repeated as desired, as indicated by s 126 . 
     While this invention has been shown and described with respect to a detailed embodiment thereof, it will be understood by those skilled in the art that changes in form and detail thereof may be made without departing from the scope of the claims of the invention.