Abstract:
A control system/method for controlling a vehicle drive-train system including an internal combustion engine, a transmission and a centrifugal clutch for drivingly coupling an engine output to a transmission input shaft. A system controller issues command output signals for controlling engine speed in order to prevent damage and/or overheating of the clutch during periods of prolonged operation of the clutch in a partially engaged state.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a vehicular transmission system utilizing a centrifugal master friction clutch. In particular, the present invention relates to an automated vehicular transmission system comprising an engine, a multiple ratio transmission, a centrifugally operated master friction clutch for drivingly coupling the engine to a transmission and a control unit for controlling fueling of the engine during prolonged operation of the centrifugal clutch in a partially engaged condition.  
         BACKGROUND OF THE INVENTION  
         [0002]    Automated mechanical transmission systems not requiring the vehicle driver or operator to operate the vehicle master clutch (so called “two-pedal systems”) are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,361,060, 4,936,428; 5,439,428; 5,634,867; 5,630,773; 5,960,916; and 5,947,847, the disclosures of which are incorporated herein by reference in their entirety. These systems are not totally satisfactory as separate clutch actuators, sensors and/or, electrical and/or fluid power (i.e., compressed air and/or hydraulic) connections thereto are required which adds to the expense of assembling and maintaining such systems.  
           [0003]    Centrifugally operated friction clutches are well known in the prior art and typically include an input member driven by a primer mover, usually an electric motor or internal combustion engine, and weights pivotable or rotatable with respect to the driving member which, upon rotation of the input member, will move radially outwardly under the effect of centrifugal force to cause the input member to frictionally engage an output member. Examples of centrifugally operated clutches may be seen by reference to U.S. Pat. Nos. 3,580,372; 3,580,372; 3,696,901; 5,437,356; 3,810,533; 4,819,779; 5,441,137; 5,730,269; and 4,610,343, the disclosures of which are incorporated herein by reference in their entirety.  
           [0004]    Vehicular transmission systems, especially for heavy-duty vehicles, utilizing centrifugal clutches permit a driver to hold the vehicle on a grade or encourage the vehicle to “creep” by increasing the speed of the engine to a point sufficient to partially engage the clutch. A drawback of this approach is that partially engaging the clutch for an extended period of time expedites wear of the friction materials and causes the clutch to develop a large amount of heat, both of which contribute to a reduction in the operative life of the clutch.  
           [0005]    A vehicular transmission system utilizing a centrifugal master clutch is disclosed in a pending U.S. patent application Ser. No. 09/814,494, filed Mar. 21, 2001, which is owned by the assignee of the present invention and is hereby incorporated by reference in its entirety. This reference discloses a control system and method of providing damage and/or overheating protection for a centrifugal clutch. Upon sensing a potential overheating problem, the control system reacts by increasing or decreasing the speed of the engine. If the engine speed is increased, the clutch will fully engage causing the driver to use a different method of maintaining the vehicle position. If the engine speed is decreased, the clutch will disengage requiring the driver to increase the throttle position to engage the clutch. While this method has proven to be effective in preventing damage and/or overheating of the clutch, the automatic engagement or disengagement of the clutch is undesirable for a driver.  
         SUMMARY OF THE INVENTION  
         [0006]    In accordance with an embodiment of the present invention, a control system and method of controlling a vehicular automated transmission system utilizing a centrifugal master friction clutch is provided. The inventive control system and method utilizes closed loop control to provide the clutch with protection from damage and/or overheating due to the clutch being operated in a partially engaged state.  
           [0007]    In a preferred embodiment, a vehicular automated transmission system is provided that includes an internal combustion engine having a flywheel, a multiple speed transmission having an input shaft and a centrifugal friction clutch drivingly connecting the engine flywheel to the input shaft. An engine controller having at least one mode of operation is utilized for controlling engine fueling to control at least the engine speed. The transmission system further includes a control unit for receiving input signals indicative of various vehicle operating conditions and processing the signals according to logic rules to issue command output signals to system actuators including at least the engine controller.  
           [0008]    The inventive control method comprises the step of first sensing vehicle operating conditions, such as, for example, vehicle acceleration or clutch temperature. Second, the control unit determines whether the clutch is being operated in a partially engaged state by comparing the sensed operating condition(s) to a predetermined reference value. Third, if it is determined that the clutch is being operated in the partially engaged state, the control unit issues an output signal to the engine controller commanding that the engine speed be repetitively increased and then decreased a predetermined amount. The increase and decrease of the engine speed causes the clutch to further engage and then disengage. The repetitive partial engagement and disengagement of clutch will not cause the vehicle to move, but will cause the vehicle to slightly shake warning the driver that clutch is being operated in a partially engaged state.  
           [0009]    Among other advantages, the inventive control system and method of controlling operation of a vehicular transmission system discourages the driver of a vehicle employing a centrifugal master friction clutch from operating the clutch in a partially engaged state for a prolonged period of time. Moreover, the inventive control system and method prevents the clutch from being automatically engaged or disengaged too quickly in the event the clutch is being operated in a partially engaged state.  
           [0010]    Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
         [0012]    [0012]FIG. 1 is a schematic illustration of a vehicular drive-train system using the centrifugal clutch and engine fuel control of the present invention.  
         [0013]    [0013]FIG. 2 is a schematic illustration, in graphical format, of the clamp force characteristics of the centrifugal clutch of the present invention at various engine speeds.  
         [0014]    [0014]FIG. 3 is a partial top view, in section, of the cover and centrifugal mechanism of the clutch of the present invention.  
         [0015]    [0015]FIG. 4 is a partial sectional view of the roller, ramp, and clamp force limiting spring mechanism utilized with the centrifugal mechanism.  
         [0016]    [0016]FIGS. 5A and 5B are partial sectional views illustrating the position of the flyweights in the fully radially inward clutch disengaged position and the fully radially outward clutch fully engaged position, respectively.  
         [0017]    [0017]FIG. 6 is a schematic partial sectional view of the present invention.  
         [0018]    [0018]FIG. 7 is a schematic illustration, in flowchart format, of the control logic of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Referring now to the drawings, the preferred embodiments of the present invention are described in detail. An at least partially automated vehicle drive-train system  20  utilizing the centrifugally operated master friction clutch of the present invention is schematically illustrated in FIG. 1. System  20  may be fully automated, as seen by way of example in U.S. Pat. No. 4,361,060, partially automated, as seen by way of example in U.S. Pat. Nos. 4,648,290 and 5,409,432, or manual with controller assist, as seen by way of example in U.S. Pat. Nos. 4,850,236; 5,582,558; 5,735,771; and 6,015,366.  
         [0020]    In system  20 , a multi-gear transmission  22  comprising a main transmission section  24 , that may or may not be connected in series with a splitter-type auxiliary transmission section  26 , is drivingly connected to an internal combustion engine  28 , such as a gasoline or diesel engine, by a centrifugal master friction clutch  30  of the present invention. Transmission  22 , by way of example, may be of the type well known in the prior art and sold by the assignee of this application, EATON CORPORATION, under the trademarks “Super-10” and “Lightning”, and may be seen in greater detail by reference to U.S. Pat. Nos. 4,754,665; 6,015,366; 5,370,013; 5,974,906; and 5,974,354, the disclosures of which are incorporated herein by reference in their entirety.  
         [0021]    Engine  28  includes a crankshaft  32 , which is attached to an input member  34  of centrifugal master friction clutch  30 . Input member  34  frictionally engages with, and disengages from, an output member  36 , which is attached to an input shaft  38  of transmission  22 . A transmission output shaft  40  extends from transmission  22  for driving connection to the vehicle drive wheels through a drive axle  41  or transfer case.  
         [0022]    The terms “engaged” and “disengaged” as used in connection with a master friction clutch refer to the capacity, or lack of capacity, respectively, of the clutch to transfer a significant amount of torque. Mere random contact of the friction surfaces, in the absence of at least a minimal clamping force, is not considered engagement.  
         [0023]    As may be seen from FIG. 1, centrifugal clutch  30  requires no external clutch actuator and is operated as a function of the rotational speed (ES) of the engine. Centrifugal clutch  30  also requires no connections to operating linkages, command signal inputs, power electronics and/or fluid power conduits. While the most economical application of the present invention is with a dry friction clutch, the present invention is also compatible with wet clutch technology.  
         [0024]    Vehicle drive-train system  20  further includes rotational speed sensors  42  for sensing engine rotational speed (ES),  44  for sensing input shaft rotational speed (IS), and  46  for sensing output shaft rotational speed (OS), and providing signals indicative thereof. A sensor  47  provides a signal THL indicative of throttle pedal position or of torque demand. The signal is usually a percentage (0% to 100%) of full throttle position. Engine  28  may be electronically controlled, including an electronic controller  48  communicating over an electronic data link (DL) operating under an industry standard protocol such as SAE J-1922, SAE J-1939, ISO 11898 or the like.  
         [0025]    An X-Y shift actuator  50 , which by way of example may be of the types illustrated in U.S. Pat. Nos. 5,481,170; 5,281,902; 4,899,609; and 4,821,590, may be provided for automated or shift-by-wire shifting of the transmission main section and/or auxiliary section. A shift selector  51  allows the vehicle driver to select a mode of operation and provides a signal GR T  indicative thereof. Alternately, a manually operated shift lever  52  having a shift knob  54  thereon may be provided. As is well known, shift lever  52  is manually manipulated in a known shift pattern for selective engagement and disengagement of various shift ratios. Shift knob  54  may be of the type described in aforementioned U.S. Pat. No. 5,957,001. Shift Knob  54  may include an intent to shift switch (not illustrated) by which the vehicle operator will request automatic engine fueling control to relieve torque lock and allow a shift to transmission neutral.  
         [0026]    System  20  further includes an electronic control unit  60  (“ECU”), preferably a microprocessor-based control unit of the type illustrated in U.S. Pat. Nos. 4,595,986; 4,361,065; and 5,335,566, the disclosures of which are incorporated herein by reference in their entirety. The ECU  60  receives input signals  64  and processes the same according to predetermined logic rules to issue command output signals  66  to system actuators, such as engine controller  48 , shift actuator  50 , and the like.  
         [0027]    As is known, to disengage a jaw clutch in a vehicular mechanical transmission, especially in a heavy-duty vehicle, it is necessary to relieve torque lock at the engaged jaw clutch. If opening the master friction clutch  30  is not desirable, torque lock can be relieved by fueling the engine to cause assumed zero drive-line torque and/or by forcing torque reversals, which will positively cause crossings of zero drive-line torque.  
         [0028]    Fully or partially automated mechanical transmission systems that, upon determining that a shift from a currently engaged ratio into neutral and then into a target ratio is desirable, will, while maintaining the vehicle master friction clutch engaged, initiate automatic fuel control to cause reduced torque across the jaw clutches to be disengaged, are also known in the prior art as may be seen by reference to above-mentioned U.S. Pat. Nos. 4,850,236; 5,582,558; 5,735,771; 5,775,639; 6,015,366; and 6,126,570. Shifting with the master clutch remaining engaged is preferred by many situations, as such shifts tend to be of a higher shift quality and/or cause less wear on the drive-line. These systems include systems that attempt to fuel the engine to achieve and maintain a zero drive-line torque, see U.S. Pat. No. 4,593,580, the disclosure of which is incorporated herein by reference in its entirety, and systems that fuel the engine to force one or more torque reversals, see U.S. Pat. No. 4,850,236. Upon sensing a transmission neutral condition, the clutch is maintained engaged and the engine speed commanded to a substantially synchronous speed for engaging a target gear ratio (ES=OSxGR T ).  
         [0029]    Control of engine torque to achieve a desired output or flywheel torque is known as and may be seen by reference U.S. Pat. No. 5,620,392, the disclosure of which is incorporated herein by reference in its entirety. Engine torque as used herein refers to a value indicative of an engine torque, usually gross engine torque, from which an output or flywheel torque may be calculated or estimated. The relationship of gross engine torque to flywheel torque is discussed in U.S. Pat. Nos. 5,509,867 and 5,490,063, the disclosures of which are incorporated herein by reference in their entirety.  
         [0030]    One or more engine torque&#39;s or torque limit values may be commanded on, or read from, an industry standard data link, DL, such as an SAE J-1922, SAE J-1939 or ISO11898 compliant datalink. By way of example, datalinks complying with SAE J1939 or similar protocol, allow the ECU  60  to issue commands over the datalink for the engine to be fueled in any one of several modes, such as (i) in accordance with the operators setting of the throttle, (ii) to achieve a commanded or target engine speed (ES=ES T ), (iii) to achieve a commanded or target engine torque (ET=ET T ) and (iv) to maintain engine speed and engine torque below limits (ES&lt;ES MAX  and ET&lt;ET MAX ). Many input/informational signals, such as engine speed (ES), engine torque (ET), and the like may also be carried by a datalink.  
         [0031]    A more detailed view of the structure of centrifugal clutch  30  may be seen by reference to FIGS.  3 - 6 . As is known, rotation of input portion  34  will cause clutch  30  to engage and drivingly connect an engine output member, usually an engine flywheel or the like, to transmission input shaft  38 . The clamping force (CF) and torque transfer capacity of clutch  30  is a function of the rotational speed (ES) of engine  28  and clutch input member  34 . Clutch  30  reaches incipient engagement at an engine speed (ES) greater than engine idle and fully engages at an engine speed lower than the engine speed at which a first upshift is required. Unlike normally closed master friction clutches that are normally engaged, clutch  20  is disengaged at lower engine speeds.  
         [0032]    To allow proper vehicle launch and dynamic shifting with the master clutch engaged, clutch  30  once fully engaged, should remain fully engaged at engine speeds greater than (i) the highest expected speed at which downshifts are initiated and (ii) the minimum expected engine speed after an upshift. Incipient engagement is the initial torque transfer contact of clutch friction surfaces as may be seen by reference to U.S. Pat. Nos. 4,646,891 and 6,022,295, the disclosures of which are incorporated herein by reference in their entirety.  
         [0033]    Referring to FIGS. 3 and 6 of the drawings, clutch  30  includes a clutch cover assembly  100 , a first friction plate  102 , an intermediate pressure plate  141 , and a second friction plate  106 . Cover assembly  100  and intermediate pressure plate  141  are mounted to the engine flywheel  136  via a mounting bracket (not illustrated) for rotation therewith and comprise the input portion  34  of clutch  30 . Friction plates  102  and  106  are typically splined to transmission input shaft  38  and comprise the output portion  36  of clutch  30 .  
         [0034]    Referring to FIGS.  3 - 5 B, cover assembly  100  includes four flyweights  110  that are pivotably mounted to cover assembly  100  at pivot pins  112 . A plurality of return springs  114  bias the flyweights  110  radially inwardly to rest on stops  116  (see FIG. 5A). A surface  118  of cover assembly  100  limits the radially outward movement of flyweights  110  (see FIG. 5B). As engine  28  and cover assembly  100  rotate, the effect of centrifugal force will cause the flyweights  110  to move against the biasing force of springs  114  from the position of FIG. 5A to the position of FIG. 5B. Flyweights  110  each carry one or more rollers  120  or functionally similar wedging member, which act between a reaction surface and a ramp to provide an axial clamping force for engaging the master friction clutch  30 .  
         [0035]    [0035]FIG. 6 is a schematic illustration of the operational members shown in fragments as rotating about a rotational axis  122  of transmission input shaft  38 . Rollers  120  of flyweights  110  are received between a substantially flat surface  124  of a fixed reaction plate  125  and a ramped surface  126  of an axially moveable ramp plate  128 . The ramp plate  128  acts on an axially movable main pressure plate  130  through a preloaded spring member  132 , such as a diaphragm spring, which limits the axial force applied to pressure plate  130  by ramp plate  128 . Main pressure plate  130  will apply a clamping force (CF) on the friction pads  134  of friction plates  102 ,  106  which are trapped between surface  130 A of the main pressure plate  130  and the intermediate pressure plate  141  and surface  136 A of the engine flywheel  136 . The hub portions  140  and  142  of the friction plates  102  and  106 , respectively, are adapted to be splined to input shaft  38  for rotation therewith while plates  125 ,  128 ,  130 , and  141  rotate with the engine flywheel  136 .  
         [0036]    At rest, one of rollers  120  will engage the recessed portion  146  of surface  126  and will not apply a leftward acting axial clamping force (CF) to friction pads  134 . As the roller  120  travels sufficiently radially outwardly and onto the ramped portion  148  of ramp surface  126 , an increasing axial clamping force is applied (see line  70  of FIG. 2). As the roller moves further radially outwardly onto the flat extended portion  150  of ramp surface  126 , the clamp force (CF) will remain at a capped value (see lines  74  and  76  of FIG. 2) as limited by spring member  132 . Applying force through a spring to limit the maximum force applied is known in the prior art as may be seen by reference to U.S. Pat. No. 5,901,823.  
         [0037]    A greater centrifugal force  152  is required to move rollers  120  up ramp portion  148  to flat portion  150  than is required to retain the rollers on flat portion  150  against the effect of a radially inward directed spring force  154  generated by return springs  114 . This accounts for the difference between the engine speed (ES) value at the initial maximum clamp force, point  72  of FIG. 2, and the release engine speed value, point  78  of FIG. 2. The relative masses of flyweights  110  and/or the spring rate of spring  114  may be modified to change the engine speed value at disengagement (point  78  of FIG. 2).  
         [0038]    As is known, to launch a heavy duty vehicle, less torque at the input shaft is required (for example, 600 to 900 lb.ft., depending on the grade) than to move the vehicle at high speeds. Typical heavy-duty vehicle diesel engines will have a maximum torque output of about 1400 to 2200 lb.ft. at a maximum torque RPM. For one embodiment of master friction clutch  30 , 1000 lbs. of clamp force will provide a torque capacity of about 600 to 700 lb.ft., while 4000 lbs. of clamp force will provide a torque capacity of 3000 lb.ft., which is well in excess of engine torque capacity and drive-line capacity and provides a large margin of safety when clutch  30  is in the capped clamp load condition (lines  74  and  76  of FIG. 2).  
         [0039]    At vehicle launch, i.e. starting the vehicle from stop, the clutch  30  should lock up at between about 750 RPM and 950 RPM, depending on whether the vehicle is starting on a steep grade or is in another high resistance condition. In the launch mode, the transition from disengagement to engagement of the centrifugal master clutch  30  is dependent upon increasing engine speed. One characteristic of a centrifugal clutch is that a driver of a vehicle is able to maintain the vehicle in a stopped position on a steep grade by operating the clutch in a partially engaged state known as “slipping” the clutch. A drawback to this approach is that prolonged “slipping” of the clutch develops a large amount of heat and the friction material is degraded, thereby reducing the life of the clutch. The control system and method of controlling a centrifugal master friction clutch according to the present invention is designed to discourage a driver from operating the clutch in a partially engaged state for a prolonged period of time.  
         [0040]    The control system comprises engine controller  48  and ECU  60 , which together function as a signaling device for commanding operation of engine  28 . The Engine controller  48  includes an output for selectively transmitting a command signal to engine  28  and engine  28  includes an input that selectively receives the command signal from engine controller  48 . Engine controller  48  further includes at least one mode of operation for controlling engine fueling to control at least the engine speed (ES).  
         [0041]    ECU  60  includes at least one input for receiving input signals and processing the signals according to logic rules to issue command output signals  66  to engine controller  48  when ECU  60  determines that clutch  30  is being operated in a partially engaged state for an excessive period of time. The command output signals  66  instruct engine controller  48  to generate at least one engine input signal having a predetermined amplitude and frequency that causes the engine speed to repetitively increase and decrease.  
         [0042]    Referring to FIG. 7 of the drawings, the control method of the present invention will be described in detail. As shown in step  300 , ECU  60  first senses at least one vehicle operating condition to determine whether clutch  30  is being operated in a partially engaged state. Constant slipping of clutch  30  may be sensed in several ways, such as, for example, sensing if vehicle acceleration is less than a reference value ((dos/dt)&lt;REF?), sensing a difference between engine speed (ES) and input shaft speed (IS), or by sensing or estimating a clutch temperature from sensed vehicle operating conditions, see U.S. Pat. No. 4,576,263, the disclosure of which is incorporated herein by reference in its entirety.  
         [0043]    Another method of determining whether clutch  30  is being operated in a partially engaged state utilizes the sensed engine speed, input shaft or output shaft speed and net engine torque to calculate the energy the clutch is absorbing. This method subtracts energy dissipated (in the form of heat) from the energy input into the clutch to determine the clutch output energy at any given period of time.  
         [0044]    ECU  60  compares the sensed operating condition(s) with a predetermined reference value of the sensed operating condition(s) to determine if clutch  30  is in a partially engaged state, as shown in steps  302  and  304 . For example, clutch  30  may be deemed to be operating in a partially engaged state if the measured clutch temperature exceeds a predetermined reference temperature. In another example, clutch  30  may be deemed to be operating in a partially engaged state if the difference between the energy inputted into clutch  30  and the energy dissipated by clutch  30  is less than a predetermined reference value.  
         [0045]    As shown in step  306 , upon sensing operation of clutch  30  in a partially engaged state for a time period (T E ) that exceeds a predetermined acceptable period of time (T REF ), such as, for example, five seconds, the ECU  60  warns the driver of excessive clutch slip, step  308 . In a preferred embodiment, the warning is provided in the form of at least one of an audible tone or a flashing light within the drivers range of vision, such as, for example, in the vehicle instrument panel. However, the form of the warning is not critical to the operation of the inventive control system permitting other warnings, such as a textual message on LCD display in the vehicle cabin, to fall within the scope of this invention. As shown in step  310 , the ECU  60  then pauses a predetermined period of time to allow the vehicle driver to comply with the warning before proceeding to the next step.  
         [0046]    Referring to steps  312  and  314 , continued, uninterrupted, operation of clutch  30  in a partially engaged state causes the ECU  60  to issue a command output signal  66  to engine controller  48  commanding the engine speed to repetitively increase and decrease, such as, for example, +/−10 RPM. In a preferred embodiment, engine controller  48  commands operation of engine  28  via a first engine input signal S n  comprising a sine wave having a predetermined amplitude and frequency. The increase and decrease in the engine speed causes clutch  30  to further engage and then disengage. The repetitive partial engagement and disengagement of clutch  30  does not cause the vehicle to move, but instead causes the vehicle to slightly shake warning the driver that clutch  30  is being operated in a partially engaged state beyond an acceptable period of time.  
         [0047]    Referring to steps  316 - 320 , if after an additional predetermined period of time clutch  30  is still being operated in a partially engaged state, ECU  60  will issue a command output signal  66  to engine controller  48  requiring it to increase the amplitude and/or frequency of the first engine input signal S n . Receipt of a second engine input signal S n+1  causes the engine speed to repetitively increase and decrease at a substantially higher RPM than the first engine input signal S n , such as, for example, +/−25 RPM. This larger swing in engine speed will cause the vehicle to shake more violently and may cause torque reversals in the drive-train. As shown in steps  322  and  324 , the process of increasing the amplitude and/or frequency of the engine input signal S n  is repeated until the driver ceases operation of clutch  30  in a partially engaged state.  
         [0048]    The inventive control system and method of controlling operation of a vehicular transmission system advantageously discourages the driver of a vehicle employing a centrifugal clutch from operating the clutch in a partially engaged state for a prolonged period of time. Moreover, the inventive control system and method prevents the clutch from being automatically engaged or disengaged too quickly in the event the clutch is being operated in a partially engaged state.  
         [0049]    Although certain preferred embodiments of the present invention have been described, the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention. A person of ordinary skill in the art will realize that certain modifications and variations will come within the teachings of this invention and that such variations and modifications are within its spirit and the scope as defined by the claims.