Abstract:
An automatic clutch control method and system includes steps for controlling a vehicle master clutch to prevent the clutch from destructively overheating due to excessive slipping. A heat buildup value is determined from various engine operating parameters, such as output torque, engine speed, and input shaft speed. The heat buildup value can be increased or decreased depending on the various engine operating parameters. A signal generating device is responsive to the heat buildup value exceeding a first predetermined heat buildup limit to generate a clutch protection output signal effective to cause the clutch to be operated in an aggressive mode of operation to fully engage the clutch at a faster rate. The signal generating device is also response to the heat build value exceeding a second predetermined heat buildup limit and slow vehicle speed to generate a clutch protection output signal effective to cause the clutch to be operated in a fully disengaged mode of operation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to clutch controls for automatically controlling the engagement and disengagement of transmission master clutches, and more particularly relates to clutch controls for master clutches utilized with mechanical transmissions, in particular with automatic mechanical transmission systems, which simulate the current clutch operating surface temperatures and automatically operate the clutch in response to a simulated temperature greater than a predetermined limit. 
     BACKGROUND OF THE INVENTION 
     Automatic mechanical transmission systems and the automatic controls for the master clutches thereof are known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,478,851; 3,752,284; 4,019,614; 4,038,889; 4,081,065 and 4,361,061, the disclosures of which are hereby incorporated by reference. 
     Briefly, in such automatic mechanical transmissions systems, various drive line operations include the supply of fuel to the engine, the engagement and disengagement of the master clutch, the shifting of the transmission and the operation of other devices such as input or output shaft brakes are automatically controlled by a control system, including a central processing unit, based upon certain measured, sensed and/or calculated input parameters. Typically, the input parameters include engine speed, throttle position, transmission input and/or output shaft speed, vehicle speed, current engaged gear ratio, application of the brakes and the like. The term throttle position is utilized to signify the position or setting of any operator controlled device for controlling the supply of fuel to an engine. 
     Referring specifically to the automatic clutch control, in a vehicle equipped with an automatic mechanical transmission, during normal operation, when starting from at rest or operating at a very low speed, the master friction clutch is modulated between fully disengaged and fully engaged conditions, i.e. is partially engaged, according to certain input parameters, to maintain the engine speed at a set value above idle speed and/or to achieve smooth starts. Typically, the set value is throttle position modulated to provide appropriate starting torque and the clutch is moved toward engagement and disengagement, respectively, as the engine speed increases above and falls below, respectively, the set value. 
     In another system, as described in U.S. Pat. No. 4,081,065, the clutch is modulated in accordance with throttle position, engine speed and engine acceleration. 
     While the above automatic mechanical transmission systems are considered to be highly advantageous, they are not totally satisfactory as, in certain start up conditions when the vehicle does not have sufficient torque in the selected gear to move the vehicle load or the vehicle does not have sufficient traction to move the load, the operator may allow the clutch to remain in the partially engaged (i.e. slipping) position for an excessive period of time which may result in excessive heat buildup in the clutch and damage thereto. Such conditions can occur in starts up a steep grade and/or in mud, sand or snow. 
     Clutch control systems utilizing temperature sensors, such as bi-metalic reed devices and the like, located in the clutch are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,072,220 and 4,199,048, the disclosures of which are hereby incorporated by reference. Automatic clutch controls having means to simulate heat buildup by monitoring throttle position and slip are known as may be seen by reference to above-mentioned U.S. Pat. No. 4,081,065. 
     In another automated clutch control system, as described in U.S. Pat. No. 4,576,263, the clutch is modulated in accordance with throttle position, engine speed and engine acceleration by simulating clutch temperature utilizing sensed and/or calculated inputs. 
     The prior art systems for monitoring and/or simulating clutch temperature to prevent heat related damage thereto are not totally satisfactory as the systems did not provide adequate automatic response to sensed conditions. They also did not interact with related automatic mechanical transmission system parameters. They often utilized relatively complicated, unreliable and/or expensive sensors which were difficult and/or expensive to produce, assemble and/or maintain. Further, the prior art systems did not measure temperature at the operating (i.e. friction) surfaces or simulate clutch heating and clutch cooling conditions to accurately simulate current clutch temperature and/or based each temperature simulation from a fixed starting point not related to a constantly maintained current temperature simulation. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the drawbacks of prior art have been overcome or minimized by providing a heat dissipation prediction method of controlling heat buildup in the clutch to protect the clutch from excessive wear and/or damage resulting from heat buildup at the friction surfaces during excessively long and/or repeated clutch slipping operations. Such undesireable clutch slipping operations can be caused to occur by inexperienced, unskilled and/or inattentive operator attempts to start the vehicle under unsuitable traction conditions, attempting to start the vehicle with insufficient torque in the selected gear ratio (often associated with attempting to start a heavy loaded vehicle up a steep grade) and/or driver riding the throttle to maintain a vehicle stationary on a hill. 
     The heat dissipation prediction method comprises the steps of determining a heat buildup value based on an engine operating parameter, comparing the heat buildup value with a first predetermined heat buildup limit, comparing the heat buildup value with a second predetermined heat buildup limit, and setting an operating mode of the clutch based on the heat buildup value. 
     The heat buildup value will be increased or decreased based on comparing the various operating parameters with a baseline threshold and a baseline slip. The clutch will be caused to engage more rapidly in an aggressive mode of operation to cease slip related heat buildup when the heat buildup value is greater than a first predetermined heat buildup limit. When the heat buildup value exceeds a second predetermined heat buildup limit and the vehicle speed is slow, the clutch will be caused to rapidly disengage in a fully disengage mode of operation. Thus, the clutch will be caused to become fully disengaged or more rapidly engaged based on the heat buildup value. 
     Accordingly, it is an intent of the present invention to provide an automatic clutch control system for determining a heat buildup value from sensed and/or calculated inputs and for operating the clutch to minimize or prevent excessive wear and/or damage thereto resulting from slip related temperature buildup. 
     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 
     FIG. 1 is a schematic illustration, in block diagram format, of an automated mechanical transmission system utilizing the integral gear life monitor system of the invention. 
     FIG. 2 is a flow chart of the heat dissipation method of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is schematically illustrated in FIG. 1 an at least partially automated mechanical transmission system  10  intended for vehicular use. The automated transmission system  10  includes a fuel-controlled engine  12  (such as a well-known diesel engine or the like), a multiple-speed, change-gear transmission  14 , and a non-positive coupling  16  (such as a friction master clutch) drivingly interposed between the engine and the input shaft  18  of the transmission. The transmission  14  may be of the compound type comprising a main transmission section connected in series with a splitter- and/or range-type auxiliary section. Transmissions of this type, especially as used with heavy-duty vehicles, typically have 6, 7, 8, 9, 10, 12, 13, 16 or 18 forward speeds. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 5,390,561 and 5,737,978, the disclosures of which are incorporated herein by reference. 
     A transmission output shaft  20  extends outwardly from the transmission  14  and is drivingly connected with the vehicle drive axles  22 , usually by means of a prop shaft  24 . The illustrated master friction clutch  16  includes a driving portion  16 A connected to the engine crankshaft/flywheel and a driven portion  16 B coupled to the transmission input shaft  18  and adapted to frictionally engage the driving portion  16 A. See U.S. Pat. Nos. 5,634,541, 5,450,934 and 5,908,100, herein incorporated by reference. An upshift brake  26  (also known as an input shaft brake or inertia brake) may be used for selectively decelerating the rotational speed of the input shaft  18  for more rapid upshifting, as is well known. Input shaft or upshift brakes are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,655,407 and 5,713,445, herein incorporated by reference. A microprocessor-based electronic control unit (or ECU)  28  is provided for receiving input signals  30  and for processing same in accordance with predetermined logic rules to issue command output signals  32  to various system actuators and the like. Microprocessor-based controllers of this type are well known, and an example thereof may be seen by reference to U.S. Pat. No. 4,595,986, herein incorporated by reference. 
     System  10  includes a rotational speed sensor  34  for sensing rotational speed of the engine and providing an output signal (ES) indicative thereof, a rotational speed sensor  36  for sensing the rotational speed of the input shaft  18  and providing an output signal (IS) indicative thereof, a torque sensor  37  for sensing the torque of the input shaft  18  and providing an output signal (IT), and a rotational speed sensor  38  for sensing the rotational speed of the output shaft  20  and providing an output signal (OS) indicative thereof. A sensor  40  may be provided for sensing the displacement of the throttle pedal and providing an output signal (THL) indicative thereof. A shift control console  42  may be provided for allowing the operator to select an operating mode of the transmission system and for providing an output signal (GR T ) indicative thereof. 
     As is known, if the clutch is engaged, the rotational speed of the engine may be determined from the speed of the input shaft and/or the speed of the output shaft and the engaged transmission ratio (ES=IS=OS*GR T ). 
     System  10  also may include sensors  44  and  46  for sensing operation of the vehicle foot brake (also called service brake) and engine brakes, respectively, and for providing signals FB and EB, respectively, indicative thereof. 
     The master clutch  16  may be controlled by a clutch pedal  48  or by a clutch actuator  50  responding to output signals from the ECU  28 . 
     Alternatively, an actuator responsive to control output signals may be provided, which may be overridden by operation of the manual clutch pedal. In the preferred embodiment, the clutch is manually controlled and used only to launch and stop the vehicle (see U.S. Pat. Nos. 4,850,236; 5,272,939 and 5,425,689, herein incorporated by reference). The transmission  14  may include a transmission actuator  52 , which responds to output signals from the ECU  28  and/or which sends input signals to the ECU  28  indicative of the selected position thereof. Shift mechanisms of this type, often of the so-called X-Y shifter type, are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,305,240 and 5,219,391, herein incorporated by reference. Actuator  52  may shift the main and/or auxiliary section of transmission  14 . The engaged and disengaged (i.e., “not engaged”) condition of clutch  16  may be sensed by a position sensor  16 C or may be determined by comparing the speeds of the engine (ES) and the input shaft (IS). 
     Fueling of the engine is preferably controlled by an electronic engine controller  54 , which accepts command signals from and/or provides input signals to the ECU  28 . Preferably, the engine controller  54  will communicate with an industry standard data link DL which conforms to well-known industry protocols such as SAE J1922, SAE J1939 and/or ISO 11898. The ECU  28  may be incorporated within the engine controller  54 . 
     In addition, the ECU  28  may be electrically coupled to the input sensor  36  and the output sensor  38  to receive input speed (IS) and the output speed (OS) signals, respectively. It will be appreciated that the invention is not limited by the ECU  28  receiving signals from the input and output sensors of the transmission, and that the invention can be practiced by the ECU  28  receiving signals from any rotating component of interest in the vehicle driveline. 
     Referring now to FIG. 2, there is illustrated a method for controlling clutch heat buildup based on one or more engine operating parameters, such as engine torque output (IT), engine input shaft speed (IS) and engine speed (ES) in accordance with the invention. Initially, the method of the invention begins at Step (S 2 . 1 ). Then, the ECU  28  determines if two conditions are satisfied: 1) if the torque output (IT) is greater than a baseline threshold value, and 2) if the engine speed (ES) is greater than the input shaft speed (IS) plus a baseline slip value (S 2 . 2 ). The baseline threshold value can be a minimum amount of torque required to cause clutch heating, for example, approximately 35 ft-lbs. The baseline slip value can be a minimum slip required to cause clutch heating, for example, approximately 50 RPM. 
     If the above two conditions are satisfied, then a Heat Buildup Value in the form of a numerical value is increased (S 2 . 3 ) by the ECU  28  as follows:          New                 Heat                 Buildup                 Value     =       Old                 Heat                 Buildup                 Value     +       [       (       engine                 speed     -     input                 shaft                 speed       )     *   torque                 output     ]       Calibration                 Value                                
     where, 
     Calibration Value is a scaling offset value that allows for a predetermined amount of heat buildup in the clutch to occur. The Calibration Value is a function of the heat sink capability of the clutch and is a function of clutch design (materials used, and the like). The Calibration Value can be determined by one skilled in the art by taking empirical measurements of clutch temperature as a function of time for a desired engine RPM, torque output and clutch slippage (%). 
     In a preferred embodiment, the Heat Buildup Value is a numerical constant value that varies linearly as a function of time. However, it is envisioned that the Heat Buildup Value can also take into consideration other engine variables, such as clutch temperature, clutch wear, and the like, so as to vary non-linearly as a function of time. 
     If the above two conditions are not satisfied, then the Heat Buildup Value is decreased (S 2 . 4 ) by the ECU  28  as follows: 
     
       
         Heat Buildup Value=Heat Buildup Value/Dissipation Rate Value≧0 
       
     
     where, 
     Dissipation Rate Value is a scaling offset that allows for a predetermined amount of clutch heat dissipation to occur. The Dissipation Rate Value can be determined by empirical measurements by one skilled in the art in a manner similar to the Calibration Value. 
     Next, the ECU  28  will determine if the Heat Buildup Value is greater than a first predetermined heat buildup limit (S 2 . 5 ). If so, then the ECU  28  will set clutch engagement/disengagement to an “Aggressive” operating mode (S 2 . 6 ). The “Aggressive” operating mode will cause the ECU  28  to engage or disengage the clutch at a faster rate than the rate of clutch engagement/disengagement prior to the “Aggressive” operating mode, thereby minimizing the amount of time the clutch slips and further heat buildup in the clutch. 
     Then, the ECU  28  will determine if the Heat Buildup Value is greater than a second predetermined heat buildup limit and the output speed (OS) is less than a preset value (S 2 . 7 ). Preferably, the second heat buildup limit is greater in value than the first predetermined heat buildup limit. The preset value may be set to a vehicle speed at which the vehicle is almost stopped, for example, 1-2 MPH. If so, then the ECU  28  will set clutch engagement/disengagement to a “Full Disengage” operating mode (S 2 . 8 ). The “Full Disengage” operating mode will cause the ECU  28  to fully disengage the clutch to minimize the amount of time the clutch slips, thereby minimizing further heat buildup in the clutch. The process continues to Step S 2 . 4  and decreases the Heat Buildup Value until clutch engagement can resume. Then, the determination system ends (S 2 . 9 ). 
     As described above, the method of the invention determines a Heat Buildup Value based on engine torque output, engine and input shaft speeds to predict clutch temperature and take preventive measures in the event that the clutch may become overheated and possibly damaged. An alternative embodiment of the method of the invention may comprise an additional step prior to Step S 2 . 5  to allow the clutch to cool down even further until the Heat Buildup Value is less than a predetermined restart heat buildup limit in order to allow normal engage/disengage of the clutch to occur. The restart heat buildup limit can be empirically determined and is preferably less than the first predetermined heat buildup limit. 
     Preferred embodiments of the present invention have been disclosed. A person of ordinary skill in the art would realize, however, that certain modifications would come within the teachings of this invention. Therefore, the following claims should be studied to determine the true scope and content of the invention.