Abstract:
A system for protecting the clutch of a vehicle from a harmful operating state. Included in the clutch protection system are means for monitoring the operating state of the clutch, along with means for estimating the amount of energy being dissipated by the clutch. A control unit compares the estimated amount of energy dissipated by the clutch to one or more predetermined threshold energy levels. One or more actions designed to reduce the amount of energy dissipated by the clutch are initiated when the estimated amount of energy dissipated by the clutch exceeds the one or more predetermined thresholds.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a clutch of a vehicle, and, more specifically, a system and method for protecting the clutch from excessive wear and potential damage.  
         BACKGROUND OF THE INVENTION  
         [0002]    A clutch is a mechanism designed to connect or disconnect power from one working part to another. In terms of vehicles, the clutch is used to transmit power from the motor to the drive train, and to disengage the motor and transmission when shifting gears.  
           [0003]    In its simplest form, the clutch can be considered as comprising two plates that can be selectively placed up against one another. One plate (flywheel) is attached to and rotated by a motor. A counterpart plate (clutch plate) attaches to a system of gears that one wants to run with the power of the motor. To transfer the power of the motor to the gears, the clutch plate is pushed up against the rotating flywheel. Upon being pressed up against one another, the two plates don&#39;t initially spin in synch. Instead, the driving plate (flywheel) rotates at a faster rate than the receiving plate (clutch plate) as the receiving plate slips against the driving plate as it rotates. This spinning of the two plates at different speeds is what results in wear and damage to the clutch. However, if the two plates become fully engaged, or locked together, frictional forces are strong enough to cause the two plates to spin at the same speed and no wear occurs.  
           [0004]    During the runnning of a vehicle, there are several operating states where the clutch is neither fully engaged or disengaged. Instead, the clutch “slips” excessively, resulting in premature wear and damage to the clutch. In response, the Applicant has developed a clutch protector system that detects and resolves these operating states, thereby reducing the amount of wear or damage subjected upon the clutch.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention relates to a vehicle clutch protection system, comprising a monitor for monitoring an operating state of a clutch, an estimator for estimating an amount of energy dissipated by the clutch, and a comparator that compares the estimated amount of dissipated clutch energy to at least one predetermined threshold energy levels. If the estimated amount of dissipated clutch energy exceeds a predetermined threshold energy level, a control unit initiates one or more actions to reduce the amount of energy dissipated by the clutch. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a simplified illustration of a clutch protection system according to one embodiment of the present invention.  
         [0007]    [0007]FIG. 2 is a simplified flow chart depicting the basic steps taken by the clutch protection system according to one embodiment while the clutch is in an urge to move state.  
         [0008]    [0008]FIG. 3 is a simplified flow chart depicting the basic steps taken by the clutch protection system according to one embodiment while the clutch is in an engage to lockup state.  
         [0009]    [0009]FIG. 4 is a simplified flow chart depicting the basic steps taken by the clutch protection system according to a second embodiment while the clutch is in an engage to lockup state.  
         [0010]    [0010]FIG. 5 is a simplified flow chart depicting the basic steps taken by the clutch protection system according to one embodiment while the clutch is under severe abuse by an operator. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    [0011]FIG. 1 depicts the vehicle clutch protection system  10  according to one embodiment of the present invention. A transmission  32 , such as an automatic transmission, is selectively engaged to a motor  30  by means of clutch  20 . Transmission  32  may be any type of transmission typically found in a vehicle, for example, the Autoshift™ system made by Eaton Corporation. Additionally, transmission  32  may have the capability to be placed in a manual operating mode, thereby allowing the operator of a vehicle to determine when transmission  32  will actually shift to another gear. Motor  30  can be any type of motor used to propel a vehicle. Typically this will be an internal combustion engine, although other types of motors, such as an electric motor, may just as easily be used with the present invention. In the illustrated embodiment, clutch  20  is a wet clutch, which typically relies on oil not only as a lubricant but also as a coolant. Of course, the clutch protection system can be adapted to work with different types of clutches. A microprocessor-based control unit  40  is connected via data links  50  to motor  30 , transmission  32  and clutch  20 . Data links  50  may be comprised of a variety of types of data communication methods. One example of a data link  50 , provided for illustrative purposes, is the J1939 link used for communication of data, such as current motor speed and torque, between a motor and a transmission system. Additionally, although only one control unit  40  is shown in FIG. 1, the invention is not limited to this. For example, the system may be designed to include two controllers, such as one in the interior of a vehicle allowing for operator input, while the second is located with the transmission system for control over clutch functions.  
         [0012]    In simple terms, the clutch protection system assess whether a vehicle clutch may be subject to possible damage, due to excessive slipping of the clutch, by calculating an estimated amount of energy dissipated by the clutch, and comparing this estimated amount of energy to one or more predetermined thresholds. Once one of these thresholds is surpassed by the estimated amount of energy being dissipated by the clutch, the system initiates one or more actions designed to place the clutch back into a safe operating state.  
         [0013]    The detailed operation of the clutch protection system according to one embodiment of the present invention will now be discussed. Based on various operating parameters, control unit  40  is able to calculate an estimated amount of energy being dissipated by clutch  20 . For illustrative purposes, consider the following equations, which provide one example of how to calculate an estimated amount of energy dissipated by clutch  20  for every period of time delta T, such as, for example, every 10 milliseconds.  
         Clutch Power=abs(Motor Speed−Input Shaft Speed)*net motor torque/7426  
         Clutch Energy=Clutch Energy+(delta T*Clutch Power)−(Cooling Rate*Previous Clutch Energy)  
         [0014]    Where:  
         [0015]    Speed unit is rpm  
         [0016]    Torque unit is lb-ft  
         [0017]    Clutch Power unit is BTU/sec  
         [0018]    Clutch Energy unit is BTU  
         [0019]    Cooling Rate=Predetermined rate at which clutch transfers energy to its surroundings  
         [0020]    7426=Constant based on the above units  
         [0021]    Initially, clutch power=0 and clutch energy is set at a predetermined default value. Subsequently, control unit  40  repeatedly calculates an estimated clutch energy, for example, every 10 milliseconds, and updates the previous values based on the most recent calculations.  
         [0022]    The system continues to calculate and revise the estimated amount of energy dissipated by the clutch as long as the clutch is in a state that allows for excessive slippage, thereby leading to premature wear and possible damage to the clutch. This excessive slippage of the clutch is characteristic of both an i) urge to move state, and an ii) engage to lockup state. Except for transient conditions, the clutch at all other times should be in either a fully engaged or fully disengaged state, thereby precluding possible damage due to excessive slippage.  
         [0023]    To illustrate an urge to move state, consider the following example. A driver stops his or her vehicle, engages the parking brake, and then exits while leaving the motor running. However, the driver forgets to place the transmission into neutral, thereby disengaging the clutch from the engine. As such, the running motor  30  is constantly urging the vehicle to move forward by transferring its energy through clutch  20  and the gears of transmission system  32 , to ultimately cause the tires to rotate. However, as the parking brake is engaged, the tires are prevented from rolling. This prevents the gears of transmission system  32  from rotating. As a result, clutch  20  is placed in a constant state of slipping, leading to excessive wear and damage.  
         [0024]    Similarly, clutch  20  is subject to excessive slipping when placed in a typical engage to lockup state. For example, consider an operator of a truck that is carrying a heavy load and is stopped on a steep incline. However, instead of using the brakes, the driver prevents the truck from rolling back down the hill by engaging the clutch  20  and throttling the engine  30  just enough to prevent the truck from moving. This places the clutch  20  in a constant state of slipping as it continuously attempts to engage and lockup with the engine  30 .  
         [0025]    According to the present embodiment, vehicle clutch  20  is protected from residing in an urge to move state for to long, thereby minimizing the exposure of clutch  20  to a potentially damaging operating state, by comparing the estimated amount of energy dissipated by clutch  20  to a clutch abuse threshold. FIG. 2 depicts a simple flow chart of the steps taken by clutch protection system  10  of the current embodiment. First, a monitor  42 , typically associated as a component of a control unit  40  with appropriate input being received from the necessary components by way of data link  50 , determines whether clutch  20  is in an urge to move state  200 . The system then uses an estimator  44 , also typically part of control unit  40 , to estimate the amount of energy being dissipated by clutch  20 . A comparator  46 , also typically part of control unit  40 , then determines whether the estimated amount of energy being dissipated by clutch  20  is above a predetermined abuse threshold level  210 , indicating that there is potential for damage to the clutch  20 . If the estimated amount of energy is not above the threshold level, the system ends its current line of inquiry and returns to the beginning of the routine. However, if the estimated amount of clutch energy exceeds the clutch abuse threshold  210 , the protection system  10  will begin to decrease the amount of “urge to move” torque  230  generated by motor  30  and applied to clutch  20 . According to the present embodiment, this decrease in torque is carried out at a constant rate, such as, for example, 15 lb-ft/sec, although other constant rates, or even variable rates, could also be readily used. This decrease in torque continues until the estimated clutch energy dissipated by clutch  20  no longer exceeds the clutch abuse threshold level  210 .  
         [0026]    Additionally, once the estimated amount of clutch energy initially exceeds the predetermined clutch abuse threshold at step  210 , an optional clutch abuse counter (not shown in FIG. 1) may be incremented by one in order to keep track of the number of times this situation occurs. An abuse timer (also not shown in FIG. 1) may also be activated at step  220 , allowing the clutch protection system  10  to keep track of the amount of time clutch  20  resides in the potentially harmful urge to move state.  
         [0027]    [0027]FIG. 3 depicts a simple flow chart depicting the steps taken by clutch protection system  10  according to a first embodiment that deals with a vehicle whose clutch is in an engage to lockup state. Unlike the analysis performed during the urge to move state, both a clutch abuse threshold and clutch damage threshold are utilized in the process of determining what actions, if any, need to be taken to protect clutch  20  from damage. In accordance with the present embodiment, the clutch abuse threshold is lower in value than the clutch damage threshold, both of which are predetermined based on the specific type of clutch installed in the vehicle.  
         [0028]    Monitor  42  first determines whether clutch  20  is in an engage to lockup state at step  300 . In addition, monitor  42  determines whether the acceleration pedal of the vehicle is at least partially depressed (step  302 ), indicating that the driver of the vehicle is currently seeking to obtain more power from motor  30  beyond that produced when in a basic idle state. If these two requirements are satisfied, comparator  46  then determines whether the estimated amount of energy dissipated by clutch  20  exceeds a predetermined clutch abuse threshold (step  304 ). If any of the above steps result in a negative answer, the current inquiry process is ended and allowed to start all over. If it is determined that the estimated amount of energy dissipated by clutch  20  does exceed the clutch abuse threshold (step  304 ), it must be determined whether the clutch damage threshold is also exceeded (step  306 ).  
         [0029]    Assuming that the estimated amount of clutch energy exceeds the clutch abuse threshold, but not the higher clutch damage threshold, the inquiry process continues on with step  308 . There an abuse counter is incremented, allowing the system to keep track of the number of times the clutch  20  has been placed in a potentially damaging state. The system also records, by means of a timer (not shown in FIG. 1), a relative abuse time stamp for the current event, and also accumulates the amount of time the clutch spends exceeding the clutch abuse threshold but below the clutch damage threshold. A warning signal is also issued at step  310 . The warning signal is directed to the operator of the vehicle, and is intended to alert the operator to the fact that he or she is abusing the clutch  20 . The warning signal can be either visual, auditory, or both. One example of a warning signal, provided for illustrative purposes, is the sounding of a continuous 1 second alert followed by 1 second of silence. Furthermore, a display on the vehicle dashboard can, for example, flash a letter “C” followed by the letter “A” to indicate that a clutch abuse state is currently present.  
         [0030]    The system  10  will continue to issue the warning signal until one of three possible conditions occurs (step  312 ). First, the warning signal will subside if the estimated clutch energy level falls below a clutch abuse signal-off threshold. This threshold can be defined in numerous ways. For instance, the signal-off threshold can simply be made equal to the clutch abuse threshold. However, this can result in repeated warning signals if the average amount of energy dissipated by clutch  20  is close to the energy level that represents the clutch abuse threshold. Expected fluctuations in the clutch energy level can lead to a frequent and repeated triggering and silencing of the warning signal as the clutch energy level repeatedly exceeds the threshold by a brief amount as the energy level routinely fluctuates. To rectify this condition, the signal-off threshold level can be set at a lower level than that of the clutch abuse threshold. Accordingly, the warning signal will issue once the clutch energy level exceeds the abuse threshold, and it will not subside until the clutch energy level drops below the abuse threshold by a predetermined amount. Once subsided, the warning signal will not issue again until the clutch energy level rises enough to once again exceed the clutch abuse threshold.  
         [0031]    The second condition that will turn off the warning signal is a change in state of clutch  20 . For example, if the vehicle operator increases the speed of the motor, thereby increasing the amount of torque applied to the clutch, or alternatively, the transmission system  32  triggers a shift in gears.  
         [0032]    The third condition that will terminate the clutch abuse warning signal is if the system, by means of control unit  40 , senses that the vehicle operator has made a conscious effort to stop abusing the clutch  20 . Various criteria can be used to define this condition, for example, the control unit  40  detecting a consecutive decrease in estimated clutch energy for a minimum duration of time, such as, for illustrative purposes, 100 milliseconds.  
         [0033]    If none of the above three conditions represented by step  312  are satisfied, the warning signal will continue to be issued. Furthermore, the system also checks on whether there has been an increase in the amount of estimated energy dissipated by the clutch (step  313 ). If there has been an increase in the amount of estimated energy, the system returns to step  306  to determine whether the amount of estimated energy now exceeds the clutch damage threshold.  
         [0034]    If any of the above three conditions represented by step  312  are satisfied, the warning signal is turned off at step  314 . However, the clutch protection system  10  does not reset itself yet. Instead, the estimated amount of energy dissipated by clutch  20  is once again calculated and compared to the clutch abuse threshold at step  316 . If the estimated clutch energy level exceeds the abuse threshold level, and continues to consecutively increase for a predetermined duration of time, the process will return to step  310  and the warning signal will once again be issued. Alternatively, if the estimated clutch energy level decreases below a clutch abuse reset threshold (step  318 ), for example, a predetermined amount below the clutch abuse threshold, the inquiry process is ended and the system resets.  
         [0035]    If it is determined that clutch  20  is in an engage to lockup state (step  300 ), that the acceleration pedal is at least partially depressed (step  302 ), and the estimated clutch energy level exceeds not only the clutch abuse threshold (step  304 ), but also exceeds the higher clutch damage threshold (step  306 ), the system continues on to step  330 . Note that steps  304  and  306  could be exchanged with one another, such that the system determines whether an estimated amount of energy dissipated by clutch  20  exceeds the clutch damage threshold first before determining whether the clutch abuse threshold is exceeded. Similar to step  308 , step  330  involves the incrementing of a clutch damage counter and the generation of a relative damage time stamp that allows the system to determine how much time clutch  20  is subject to damage.  
         [0036]    At this point, it can be determined that the clutch  20  is in a typical engage to lockup state, such as when an operator has stopped his or her truck on an incline and is using the clutch instead of the brakes to keep the truck from rolling backwards. In this instance, the control unit  40  attempts to cause clutch  20  to fully engage the motor  30 , thereby preventing any more damage caused by excess slipping of the clutch  20 . This is accomplished by increasing the rate at which clutch  20  engages motor  30  (step  334 ). As the rate of clutch engagement increases, the chance of clutch damage due to slippage decreases. The end result is the full engagement of clutch  20 , leading the truck or vehicle to begin to accelerate.  
         [0037]    According to a further embodiment, the increased rate of clutch engagement is not a constant, but instead variable depending on how much energy is being dissipated by clutch  20 . The greater the amount of energy in clutch  20 , the farther the clutch damage threshold is exceeded, resulting in an increased rate of damage to clutch  20 . Accordingly, it would seem preferable to have clutch  20  fully engage the motor  30  as fast as possible, thereby minimizing the amount of time that clutch  20  is excessively slipping and subject to damage. However, in contrast, one would also prefer to have clutch  20  slowly engage motor  30 , thereby providing more time for the operator of the vehicle or truck to react to the fact that their vehicle is beginning to accelerate.  
         [0038]    To best satisfy both of the above requirements, the system is designed so that the farther an estimated clutch energy exceeds the predetermined clutch damage threshold level, the faster the rate of clutch engagement. Accordingly, if a clutch energy level only mildly exceeds the clutch damage threshold, the rate of clutch engagement will increase modestly. In contrast, if the clutch energy level significantly exceeds the clutch damage threshold, rate of clutch engagement will be increased significantly as well.  
         [0039]    While the system is increasing the rate of clutch engagement in order to prevent any further damage to the clutch  20  due to slippage, the control unit also initiates a warning signal to the vehicle operator (step  336 ) to alert them to the fact that the clutch is in the process of fully engaging motor  30 . Similar to before, the warning signal can be any type of auditory warning, visual warning, or combination thereof, as long as it alerts the vehicle operator to the clutch engagement and provides them with time to react properly.  
         [0040]    The warning signal continues to sound and/or display until the estimated energy being dissipated by clutch  20  drops below a damage signal-off threshold, which is set at a predetermined amount below the clutch damage threshold. If the clutch energy level does drop below this damage signal-off threshold, the warning signal ceases, as indicated in step  362 .  
         [0041]    Similar to the abuse reset threshold of step  318 , a damage reset threshold is employed at step  364 , keeping the current process active until the estimated clutch energy level drops significantly enough to end the process (step  380 ) and reset the system.  
         [0042]    In another embodiment of the invention, the vehicle employing the clutch protection system of the present invention may have a transmission system that allows an operator to place it in a manual mode of operation. Thus, instead of the transmission system  32  automatically shifting gears without input from the vehicle operator, the operator controls when a shift in gears is to occur. However, a disadvantage of this manual shifting-based system is that it allows for another unique situation where clutch  20  can be placed in a damaging operating state.  
         [0043]    Some transmission systems  32  have the ability to be placed in a manual mode of operation where the vehicle operator determines when the transmission system  32  shifts between gears. However, in this mode, the vehicle can be driven in a manner as to place clutch  20  in another type of engage to lockup state. In this situation, however, instead of an operator trying to hold a vehicle stationary on an incline by means of the clutch  20 , the vehicle is moving. Consider the following example, provided for illustrative purposes. An operator has his or her vehicle currently in a high gear and is approaching a red light. The operator begins to slow the vehicle down without disengaging the clutch  20  or downshifting the transmission system  32 . Due to the slow speed, clutch  20  begins to unlock or disengage. At this point in time, the light turns green and the operator begins to accelerate their vehicle, still without shifting to a lower gear. This causes the clutch to excessively slip. Unlike the previous engage to lockup situation, one doesn&#39;t want to engage the clutch while the transmission system  32  remains in a high gear as it can cause the motor  30  to stall. The clutch protection system according to the current embodiment solves the above problem by temporarily overriding the manual shift mode and causing the transmission system  32  to automatically shift to a lower gear.  
         [0044]    As depicted in FIG. 4, if the clutch is in an engage to lockup state (step  400 ), and the accelerator pedal of the vehicle is at least partially depressed (step  402 ), the system then determines whether the acceleration of the vehicle corresponds to the amount of acceleration that should correspond to the current position of the depressed accelerator pedal (step  404 ). Additionally, the system also checks to see if the amount of estimated energy dissipated by the clutch exceeds the clutch damage threshold (step  404 ). If the vehicles actual acceleration does not correspond to the acceleration expected, or if the estimated clutch energy does exceed the clutch damage threshold, the system increments a counter and generates a time stamp (step  430 ) as done in previous embodiments. It must also check to confirm that the transmission system  32  has been placed in a manual operating mode (step  432 ). Upon confirmation of this condition, the control unit  40  determines whether the current gear the vehicle is in is the gear used to start the vehicle (step  442 ). This check is necessary to assure that a lower gear is available to shift down into. Assuming that the vehicle is not in one of the lower starting gears, the control unit  40  causes the transmission system  32  to down shift. At the same time, a warning signal similar to that of step  336  is initiated. Steps  460 - 480  are then repeated in the same fashion as they were carried out in the engage to lockup situation involving a transmission system  32  not placed into a manual operating mode.  
         [0045]    According to another embodiment of the present invention, the clutch protection system  10  will attempt to prevent damage to clutch  20  caused by a vehicle operator severely abusing the clutch  20 . As depicted in the flow chart of FIG. 5, this mode of operation requires three conditions. First, the clutch protection system  10 , by means of the control unit  40 , must detect the accelerator pedal being at least partially depressed (step  500 ), indicating that the vehicle operator is seeking increased power from motor  30 . Additionally, it must also determine that a braking system of the vehicle, such as, for example, the service brakes or parking brakes, are currently engaged (step  502 ), indicating that the operator is accelerating and braking the vehicle at the same time. Upon meeting these two conditions, the system assesses whether the estimated amount of energy dissipated by clutch  20  exceeds the clutch damage threshold. The system then proceeds to increase the rate of clutch engagement just as it did in step  334  of FIG. 3, except in this embodiment, an additional predetermined amount, for example, 30 lb-ft/sec, is added upon to the prior amount that the rate of clutch engagement was increased by in the prior embodiment. Thus, if the rate of clutch engagement was increased by 20 lb-ft/sec at step  334 , the rate of clutch engagement in this embodiment would be increased by 50 lb-ft/sec. All further steps depicted in FIG. 5 are the same as those that follow step  334  of FIG. 3, and will not be discussed in any further detail.  
         [0046]    In a further embodiment of the Applicant&#39;s invention, the clutch protection system  10  is designed to provide limited functions in the event of a data link failure. For example, if the J1939 data link between the control unit  40  and motor  30  were to fail, the system will continue to estimate the amount of energy dissipated by the clutch  20 , initiate warning signals when appropriate, and record abuse/damage information provided by the appropriate counters and timers. However, as the clutch protection system  10  can no longer deliver control data to motor  30 , activities such as decreasing the amount of torque applied to clutch  20  will any longer be capable.  
         [0047]    In many of the embodiments disclosed above, the clutch protection system issues a warning signal as one type of action designed to reduce the amount of energy dissipated by clutch  20 . It was previously emphasized that these warning signals (i.e. steps  314 ,  336 ,  446  and  508 ) can be either auditory, visual, or a combination thereof. Furthermore, these warning signals can all be of the same type of alert, or, if desired, they can be different so as to be distinguishable from one another. For example, it may be desirable to have the warning signal (step  310 ) issued upon a clutch energy exceeding the clutch abuse threshold to be audibly or visually different than the warning signal (step  336 ) issued when the system is increasing the rate of clutch engagement.  
         [0048]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.