Abstract:
A vehicle having a chassis, an engine supported by the chassis, a clutch assembly and a controller. The clutch assembly contains a clutch that is coupled to the engine. The controller executes a method to protect the clutch, the method including the steps of calculating, comparing and derating. The calculating step includes calculating the amount of energy being absorbed by the clutch. The comparing step compares the amount of energy to a predetermined limit. The derating step derates the engine dependent upon whether the amount of energy exceeded the predetermined limit in the comparing step.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an engine with a clutch attached thereto, and, more particularly, to an engine/clutch combination with a clutch protection method and apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    A power source, such as an engine is often connected to a clutch assembly, which allows for the selective engagement and disengagement of rotating power from the power source to a load. Often the engine is connected by way of the clutch to a transmission, for example in a vehicle. Clutches typically are employed in devices which have two rotating shafts. One shaft is typically connected to the power unit and the other shaft provides the output power to the transmission or load. The clutch connects the two shafts so that they may be locked together and spin at the same speed when they are in an engaged position and the shafts may spin at different speeds when the clutch is disengaged. Clutches typically depend upon a frictional interface between a plate connected to one shaft and a plate connected to another shaft with the clutch often having a surface with a known frictional coefficient that is durable enough to withstand the demands of the power transfer through the clutch assembly. Organic and ceramic frictional materials are typically used. 
         [0003]    There are dry clutches and wet clutches with the dry clutch being, as the name implies, literally dry. A wet clutch is immersed in a fluid that functions as a cooling and lubricating fluid and it keeps the surfaces clean giving smooth performance and longer life of the clutch assembly. Wet clutches lose some energy to the liquid, which then allows for cooling of the clutch. Since the surfaces of a wet clutch can he somewhat slippery the stacking of multiple clutch discs are often used to compensate for the lower coefficient of friction to help eliminate any slippage under power when the clutch disks are engaged. 
         [0004]    There is a safety clutch also known as a slip clutch that allows a rotating shaft to slip when a higher than normal resistance is encountered in the machine application. For example, a safety clutch may be employed in a grass mower so that the safety clutch will yield in the event that a blade hits an immovable object to thereby prevent damage to the mower. 
         [0005]    What is needed in the art is a clutch system that detects potential degraded performance in the clutch and takes steps to protect the clutch in an effective manner. 
       SUMMARY 
       [0006]    The present invention provides a method of protecting a clutch assembly in a vehicle including the steps of calculating an amount of energy absorbed by a clutch, comparing the energy to a predetermined limit, and derating an engine coupled to the clutch. The engine being derated dependent upon whether the amount of energy exceeds a predetermined limit in the comparing step. 
         [0007]    The invention in another form is directed to a vehicle having a chassis, an engine supported by the chassis, a clutch assembly and a controller. The clutch assembly contains a clutch that is coupled to the engine. The controller executes a method to protect the clutch, the method including the steps of calculating, comparing and derating. The calculating step includes calculating the amount of energy being absorbed by the clutch. The comparing step compares the amount of energy to a predetermined limit. The derating step derates the engine dependent upon whether the amount of energy exceeded the predetermined limit in the comparing step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0009]      FIG. 1  is a schematical top view of an embodiment of the clutch system of the present invention utilized by a power transfer apparatus as part of a vehicle; and 
           [0010]      FIG. 2  is a schematical view of an embodiment of the method employed by the clutch protection system of  FIG. 1 . 
       
    
    
       [0011]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0012]    Referring now to the drawings, and more particularly to  FIG. 1 , there is illustrated a vehicle  10  having a power system  12  that is connected to various parts of vehicle  10 . Power system  12  is situated on a chassis  14  of vehicle  10 . Power system  12  includes an engine  16 , a clutch assembly  18  having a clutch  20  and a clutch cooling system  22 . Connected to clutch assembly  18  is a load  24 . Load  24  represents any load that is being driven by engine  16  by way of clutch assembly  18 , including a transmission that may immediately follow and be connected to clutch assembly  18 . Engine  16  may be an internal combustion engine such as a diesel engine and with the use of the present invention, engine  16  may be a high power engine while clutch assembly  18  may be a clutch assembly  18  that would normally not be associated with engine  16  except for the ability of the present invention to protect clutch assembly  18  and thereby power system  12 . 
         [0013]    Additionally associated with power system  12  is a controller  26  that interacts with engine control unit  28 , shaft speed sensor  30 , shaft speed sensor  32  and a load sensor  34 . Additionally controller  36  interfaces with clutch cooling system  22 . The term interface is broadly applied and includes providing information to and receiving information from various interconnections. Controller  26  is illustrated as a separate device but it may be incorporated into engine control unit  28  or be separately positioned on chassis  14  or be associated directly with clutch assembly  18 . Controller  26  and the methods carried out therein may be carried out in a digital, analog or a combination of digital and analog electrical embodiments. Further, it is also anticipated that the present method may be carried out with fluidic logic or other fluidic control systems. For the sake of clarity it will be assumed that controller  26  is an electrical digital controller. Controller  26  has a processing system as well as memory for the storage of data and programming steps including the steps of method  100  illustrated in  FIG. 2 . 
         [0014]    Now, additionally referring to  FIG. 2  there is illustrated a method  100  for explanation of an embodiment of the present invention. Method  100  includes using information coming from an engine speed sensor at step  102  and more specifically the speed of the shaft coming from engine  16  which is sensed by shaft speed sensor  30 . The output speed of the top shaft transferring power from clutch assembly  18  is measured by shaft speed sensor  32 , which takes place at step  104 . The input speed measured at step  102  and the output speed measured at step  104  are compared to result in a clutch slip speed at step  106 . The clutch slip speed is a calculated value and may be the difference between the input speed at step  102  and the output speed at step  104  to thereby compute the clutch slip speed of step  106 . Controller  26  receives the clutch pressure at step  108  which is measured by a sensor in clutch assembly  18 . The clutch pressure is combined with the pressure to torque coefficient, illustrated at step  110 , the combination of the clutch pressure From step  108  having the pressure to torque coefficient from step  110  applied thereto results in the clutch torque at step  112 . Mathematical elements associated therewith may be a multiplication between the clutch pressure obtained at step  108  and the use of the coefficient from step  110 . The pressure to torque coefficient is a constant that is determined by the geometry or the clutch such as the size of the plates and the number of plates in the clutch assembly  18 . 
         [0015]    The clutch slip speed from step  106  and the clutch torque from step  112  are combined mathematically, for example by way of multiplication; the result is the instantaneous clutch power at step  114 . This is a calculation of the power absorbed by clutch assembly  18  and is not being transmitted by way of the output shaft. Instantaneous clutch power is a measure of power being absorbed potentially by the fluid of a wet clutch assembly. 
         [0016]    The clutch solenoid in clutch assembly  18  is either activated or not activated, either under the control of controller  26  or as detected by a sensor detecting the activation of the clutch solenoid at step  116 . If the clutch solenoid is on, as detected in step  118 , then method  100  proceeds to step  122  where a high cooling condition of clutch assembly  18  is being undertaken. If the clutch solenoid is detected as not being on, at step  118 , then low cooling is the mode of operation as illustrated by step  120 . Information as to whether clutch cooling system  22  is active at a low or high level is combined with the instantaneous clutch power from step  114  to result in the overall calculation of the clutch energy being absorbed by clutch assembly  18  at step  124 . The instantaneous clutch power and the effect of cooling system  22  is integrated over time to calculate the absorbed clutch energy at step  124 . This calculation is a cumulative calculation such as integration or as digital numeric integration of data values arrived at over short time intervals, such as 100 msec time intervals. This calculated absorbed energy of clutch assembly  18  is then compared to a predetermined value at step  126  to determine if the absorbed clutch energy is over the predetermined limit. If the clutch energy is over the predetermined limit then method  100  proceeds to step  128  in which engine control unit  28  is either requested or commanded to derate the power output of engine  16  by a predetermined value, such as 15%. This is carried out by controller  26  sending information to engine control unit  28  to derate engine  16 . Method  100  then proceeds to step  130  where method  100  is repeated, perhaps, for example, every 100 milliseconds. If at step  126  it is determined that the clutch energy is not over the predetermined limit then method  100  proceeds to step  130  in which method  100  is repeated. 
         [0017]    The present invention protects not only the clutch assembly  18  but may additionally protect elements of load  24  such as a transmission. If the clutch energy calculated at step  124  exceeds a specified threshold at step  126 , controller  26  requests that engine  16  be derated by the predetermined amount of 15%, although other values are also contemplated. When the cumulative clutch energy is measured at step  124  and it is less than a second predetermined limit, which is less than the limit used at step  126  to determine that engine  16  should be derated at step  128 , then the request for the engine to be derated is removed and the power potentially available from engine  16  is subsequently increased. The second predetermined limit may be 80% (although other values are also contemplated) of the limit used in step  126  to determine that engine  16  should be derated, thus providing for a hysteresis in the system to prevent the engine power from changing excessively when the absorbed energy lingers around the predetermined limit used to derate engine  16 . 
         [0018]    The clutch slip speed at step  106  can also be thought of as a clutch slip percentage if a ratio is computed from the input shaft speed at step  102  and the output shaft speed at step  104 . These are calculated if engine  16  is running and clutch  20  is partially or fully engaged. The clutch slip speed in RPMs can he calculated as the absolute value of: 
         [0000]      ((Engine Speed×Current Gear Ratio)−Top Shaft Speed)
       with the Current Gear Ratio referring to any gearing that is present between engine  16  and clutch assembly  18 , which once applied to the Engine Speed yields the speed of the input shaft of clutch assembly  18 .       
 
         [0020]    The Clutch slip percentage can be calculated as: 
         [0000]      Ratio=Top Shaft Speed/(Engine Speed×Current Gear Ratio)
 
         [0000]      % Slip=(1−Ratio)×100%
 
         [0000]      Slip=(100−[(Top Shaft Speed×100)/(Engine Speed×Current Gear Ratio)])
 
         [0021]    Cumulative clutch enemy can be expressed in decajoules. Cumulative clutch energy that is calculated at step  124  can he initialized to zero at the power-up of power system  12 . The cumulative clutch energy can he a positive value for example in the range of 0-64,000. If engine  16  is running and clutch  20  is engaged, either partially or fully, the following actions are taken as a calculation of the instantaneous clutch energy; the instantaneous clutch energy is added to the cumulative clutch energy at step  124 ; a calculation is carried out to compute the cooling clutch energy which is then subtracted from the cumulative clutch energy. There is also a relationship between the clutch input torque and the measured pressure of the traction clutches. The clutch input torque is mapped to measured enable pressure using the following relationship: 
         [0000]      Input_Torque [Nm]=Measured_Enabled_Pressure [kPa]×0.6−140
 
         [0022]    There can be table data populated with the clutch cooling rate versus the measured enabled pressure for the forward traction clutch. Clutch  20  cooling rates retrieved from this table can be interpolated with respect to the pressure. This table can be thought of as the clutch cooling rate versus enabled pressure and is provided as an example: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Enable 
                 Heat Removed [kJ/sec] 
               
               
                   
                 Pressure 
                 [kJ/sec] −&gt; [decajoules for each 
               
               
                   
                 [kPa] 
                 100 msec] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1500 
                 42.0 −&gt; 420 
               
               
                   
                 1425 
                 42.0 −&gt; 420 
               
               
                   
                 1350 
                 42.0 −&gt; 420 
               
               
                   
                 1275 
                 42.0 −&gt; 420 
               
               
                   
                 1200 
                 42.0 −&gt; 420 
               
               
                   
                 1125 
                 42.0 −&gt; 420 
               
               
                   
                 1050 
                 42.0 −&gt; 420 
               
               
                   
                 975 
                 42.0 −&gt; 420 
               
               
                   
                 900 
                 42.0 −&gt; 420 
               
               
                   
                 825 
                 42.0 −&gt; 420 
               
               
                   
                 750 
                 42.0 −&gt; 420 
               
               
                   
                 675 
                 42.0 −&gt; 420 
               
               
                   
                 600 
                 42.0 −&gt; 420 
               
               
                   
                 525 
                 42.0 −&gt; 420 
               
               
                   
                 450 
                 42.0 −&gt; 420 
               
               
                   
                 375 
                 42.0 −&gt; 420 
               
               
                   
                 300 
                 42.0 −&gt; 420 
               
               
                   
                 225 
                 31.5 −&gt; 315 
               
               
                   
                 150 
                 15.8 −&gt; 158 
               
               
                   
                 75 
                 6.6 −&gt; 66 
               
               
                   
                 0 
                 6.6 −&gt; 66 
               
               
                   
                   
               
             
          
         
       
     
         [0023]    Once the clutch input torque is known at step  112  power going into clutch  20  can be calculated by multiplying the clutch input torque by the clutch slip speed and dividing by a constant. Factoring in time then converts the clutch power to clutch energy, which is undertaken in step  124 . Controller  26  carries out the calculation in units of decajoules. A software implementation is illustrated in the following calculations and rules: 
         [0000]      Clutch Power=(input_Torque(Nm)*clutch_slip_speed(RPM))/9550 [kW] 
         [0000]      Clutch Energy every 100 msec=Clutch Power*Time=Clutch Power*100 ms=Clutch Power/10, 
         [0000]      Clutch Energy every 100 msec=[input_Torque*clutch_slip_speed]/95500 [kJ] 
         [0000]      Clutch Energy every 100 msec=[input_Torque*clutch_slip_speed]/9550 [0.1 kJ] 
         [0000]      Clutch Energy every 100 msec=[input_Torque*clutch_slip_speed]/955 [0.01 kJ] 
         [0000]    converting to units of decajoules 
         [0024]    As another way of understanding the present invention, it can be thought of as a set of rules that can be executed by a rule driven processing system, those rules being:
       Rule 1—If cumulative clutch energy’ exceeds a first threshold value, then controller  26  shall request a 15% engine power derate.   Rule 2—If engine power is being derated AND cumulative clutch energy is less than a second (lower) threshold, then controller  26  shall stop requesting the engine power derate.       
 
         [0027]    Additional Alternative Rules:
       Rule 3—If cumulative clutch energy exceeds the first threshold, then controller  26  shall report a fault code that indicates that the clutch has been slipping for too long.   Rule 4—If the fault code indicating that the clutch has been slipping for too long is active AND the cumulative clutch energy is less than the second threshold, then controller  26  shall slop reporting the fault code.       
 
         [0030]    The present invention advantageously protects the clutch assembly from being overdriven when it is detected that clutch  20  is slipping along with the detection of clutch energy being increasingly absorbed in clutch assembly  18 . This advantageously allows for coupling of a higher power engine  16  to clutch assembly  18  as well as reducing the amount of needed maintenance, since clutch assembly  18  is protected by the present invention. Although not illustrated it is understood that information about the function of method  100  can he presented to an operator by way of an operator interface and data obtained can also be stored in memory for later retrieval by maintenance personnel. 
         [0031]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.